MASTER THESIS The limiting similarity of seed size and resource-

based suppression: A glasshouse experiment

Phillip Hughes Matriculation Number: 03637295

Study Programme: (MSc) Master of Science Sustainable Resource

Management

Supervisors: Prof. Dr. Johannes Kollmann & Florencia Yannelli Chair of Restoration Ecology Technische Universität München

Master Thesis

1

Table of Contents

Chapter 1: Introduction and Background ....................................................................................... 2

Introduction to the driver for the research ........................................................................................ 2

Background knowledge pertinent to the research ............................................................................. 3

Restoration and succession ............................................................................................................ 3

Assembly Rules ............................................................................................................................... 4

Functional Traits ............................................................................................................................. 7

Limiting Similarity ........................................................................................................................... 7

Invasion by a Species ...................................................................................................................... 9

Chapter 2: The Glasshouse Experiment ....................................................................................... 10

Introduction ..................................................................................................................................... 10

Materials and Methods .................................................................................................................... 13

Species Selection ........................................................................................................................... 13

Seed Preparation and Germination Trials ..................................................................................... 14

Experimental Design ..................................................................................................................... 15

Variables and Measurement ........................................................................................................ 20

Data Analysis ................................................................................................................................ 20

Results .............................................................................................................................................. 22

Species-specific results ................................................................................................................. 22

Combined Results ......................................................................................................................... 25

Discussion ......................................................................................................................................... 27

Conclusion .................................................................................................................................... 28

Chapter 3: Final Discussion and Conclusion ................................................................................. 29

Acknowledgements .................................................................................................................... 31

References ................................................................................................................................. 32

Appendices ................................................................................................................................ 37

1. Seed Collection Locations ......................................................................................................... 37

2. Exact Seed Mixtures per Replicate ........................................................................................... 38

3. The exact timing of the various stages of the experimental set-up. ......................................... 39

Master Thesis

2

Chapter 1: Introduction and Background

“When we look at the plants and bushes clothing an entangled bank, we are tempted to

attribute their proportional number and kinds to what we call chance. But how false a view

that is! Everyone has heard that when an American forest is cut down a very different

vegetation springs up; but it has been observed that ancient Indian ruins in the Southern United

States, which must formerly have been cleared of forests, now display the same beautiful

diversity and proportion of kinds as in the surrounding forests.” – Charles Darwin, On The

Origin of Species, 1858

This quote at the beginning of a paper by Young (2001) has also been used here in the same

way, as it so eloquently introduces the following discussion.

Introduction to the driver for the research

Human impacts around the world are causing the degradation and loss of ecosystem diversity

at an exponentially increasing rate (United Nations Environmental Programme 2005). There

are many drivers of this loss, land clearing for agriculture is the greatest driver, yet with ever

increasing global trade and transport, Invasive Alien Species (IAS) are themselves now a

significant driver for overall biodiversity loss (Secretariat of the Convention on Biological

Diversity 2010). To put this into perspective, nearly a quarter of the earth was once covered

by grasslands and in the United States alone, 95% of the original grassland has disappeared

converted to cropland (World Wildlife Fund 2014). The common approach of monoculture

cropping not only reduces biodiversity it also facilitates IAS establishment and spread (Poggio

2005). Compounding the problem of IAS introductions is the ever increasing levels of

worldwide trade and travel, and the breakdown this causes of the natural dispersal

mechanisms (Secretariat of the Convention on Biological Diversity 2010). In the worst case

scenario, this trend could be leading to the homogenisation of the world’s plant biota (United

Nations Environmental Programme 2005)

Roadsides are interesting experimental sites, since they represent a common place for

infestation by IAS due to the high propagule pressure and nitrogen enrichment as a result of

exposure engine exhausts. The reactive approach to the presence of IAS usually consists of

eradication attempts post invasion (e.g. herbicide application). In 2007 alone, herbicides

Master Thesis

3

totalling 2.4 billion kilograms were used worldwide (Grube et al. 2011). Besides having direct

non-target effects, the most common herbicide, glyphosate, has significant in-direct toxicity

issues (Philipp Schledorn 2014). A more proactive and sustainable approach to IAS control

could be found by making appropriate choices of plants based on functional groups and

therefore formulating resilient communities de novo (Price & Pärtel 2013).

This paper and experimental work will focus on reducing a knowledge gap with respect to IAS

control and restoration ecology theory. The following section aims to introduce the pertinent

current state of knowledge. Of particular importance is the introduction to the limiting

similarity hypothesis and its potential use in practical restoration approaches (Funk & Cleland

2008).

Background knowledge pertinent to the research

Restoration and succession

Restoration ecology itself is a multidisciplinary approach that harness´s concepts from many

disciplines including landscape ecology, invasion biology, disturbance ecology, conservation

ecology and ecological succession. In essence it is a sub-discipline of ecology focusing on

themes such as biodiversity, resilience, sustainability and often addresses economic and

political issues as well (Hobbs & Harris 2001). The successful application of restoration ecology

in a practical sense is firmly based on an understanding of a range of ecological principles (Falk

et al. 2006). Therefore, restoration ecology is a practical management science, very much

governed with socioeconomic and political constraints (Walker, Walker, & Hobbs, 2007,

Costanza et al., 2014).

A basic view is that restoration is a human conducted manipulation of succession (Walker et

al. 2007). For instance, in the case of successful restoration efforts with respect to invasion of

native plant communities by alien species, this could be regarded as the succession of the

native community by the invasive species. The restoration efforts merely manipulated this

successional trajectory in favour of one that restored the native communities ‘pre-invasion’

successional trajectory (Clewell et al. 2004).

Succession is the temporal change of species composition over time (Hobbs & Harris 2001).

Topics to include when understanding succession would be things such as competition,

Master Thesis

4

priority effects, facilitation and invasive species. Interestingly, although these basic topics are

seemingly well understood, the combination of the individual effects of these to produce the

myriad of successional trajectories is not (Laughlin 2014). A perfect understanding, or rule set

of succession does not exist and of course this is beyond the scope of this paper to elucidate

one. Restoration, on the other hand, is the manipulation of a disturbed habitat into a desired

condition. It is focused on specific outcomes or actions, rather than trying to understand

vegetation change itself (Clewell et al. 2004). Hence, restoration focuses on habitats impacted

by or relevant to humans. It attempts to bring ecological principles into restoration actions.

Understanding more about succession has many benefits for the field of restoration.

Succession offers both predictions on species dynamics and suggests likely outcomes

following management actions. Essential knowledge used to predict and understand

succession such as functional plant groups, species filters and ecosystem assembly also carry

over into restoration application(Temperton et al. 2013).

This brief discussion on the relation between the overarching topics restoration and

succession moves into the next sections of the paper which will explore more deeply how

factors such as assembly rules, functional grouping and limiting similarity could provide more

insight into the field of restoration ecology with respect to invasion resistance.

Assembly Rules

Ecology today is standing on the shoulder of giants. Darwin, Gleason, Clements, MacArthur

and Wilson are the names. They asked the questions, how do communities of organisms come

to be the way they are, and what are the constraints on membership in a community. The

definitive answers to which have still not been found and have sparked close to a century of

debate. Nature evades simple description (Temperton et al. 2013). What is known is that both

stochastic and deterministic processes contribute to the formation of community

assemblages and that the recent developments reside somewhere within the conceptual

gradient bounded between the two (Götzenberger et al. 2012).

The concepts of succession and assembly rules are related, yet are importantly distinct.

Succession theory follows the dynamics of change in a community’s development, whereas

community assembly theory focuses more on the interactions between organisms and their

Master Thesis

5

environment and the actual pathways a community can take in response to such interactions

(Young et al. 2001).

Of interest to note, and rather pertinent, is the idea that assembly rule theory although

underpinning community assembly theory is not equal with it. Assembly rule theory seeks to

explain non-random similarities in guild structure across communities that differ in their

component species (Weiher et al. 1998). On the other hand, community assembly theory looks

at the processes that establish a community in such a way that multiple stable community

states may occur as a direct result of species colonisation and interactions between the

species (Young et al. 2001).

The term “assembly rule” was introduced to ecology in a paper describing species

combinations among birds in new guinea in which seven rules were posited (Cody & Diamond

1975). This work was challenged shorty after by (Connor & Simberloff 1979) where each rule

was systematically explored and debunked. The point is though, the theory of assembly rules

and the exploration of their potential had formerly begun and these two papers in my view

epitomise the conceptual gradient that still exists between stochastic and deterministic views

of community assembly.

A plant community assembles based on a range of hierarchical ecological filters that act at

increasingly finer scales (Cody & Diamond 1975; Weiher & Keddy 1995; Götzenberger et al.

2012; de Bello 2012; Chalmandrier et al. 2013; Laliberté et al. 2013).

Master Thesis

6

Figure 1. The range of scales proposed ecological filters that can act to lead to an actual observed community (Adapted from Götzenberger et al., 2012.).

The theory is such, that from the global species pool, a regional species pool is then defined

by historical and biogeographical processes (‘phylogeographic assembly’; (Kembel 2009). This

can be viewed as the gradients of species richness associated with latitude and elevation, in

that plants species richness often increases near the equator and decreases with elevation,

the historical mechanisms for which are numerous (time from colonisation, rates of

extinction/diversification, etc.). From the regional species pool dispersal and the abiotic

environment (e.g. climate) act to filter adapted species into the local species pool. From the

local species pool, habitat filtering and biotic assembly rules will define the actual community

of plant species (Figure 1). Articulately put, assembly rules are a community level analogue of

natural selection (Keddy 1992). At the actual community level, which is the purpose of this

paper to explore, species interactions (e.g. competition) are driving assembly (Mouchet et al.

2010).

Master Thesis

7

Functional Traits

The use of functional traits when understanding assembly rules is persuasively surmised with

the following comparison between species based assembly rules and those that are trait

based:

“A species form of ‘rule’ might be: if a community has species A, then it usually will not also have species B or C unless species D or E and either species F or G are present, while if a

community has species D, then it will not also have species E unless species F or G and either species A, B, or C are also present, etc. A more trait based rule is clearer: the proportion of

species from each functional group will tend to remain constant for each observation.” (Weiher & Keddy 1995)

From this quotation it is easy to understand why there is growing recognition that

classification of plant species based on their function, as opposed to their taxonomic identity,

is a more pragmatic approach to addressing ecological questions such as community structure

and vegetation response to environmental change (Cornelissen et al. 2003).

Violle et al. (2007) have concisely formulated a definition of functional trait with respect to

plants, suggesting it is any trait which impacts the fitness indirectly via its effects on growth,

reproduction and survival. The paper also makes the further distinction of a so called

‘performance trait’, that being a direct measure of fitness, and in plants only three such traits

are recognized: vegetative biomass, reproductive output (e.g. seed biomass, seed number)

and plant survival (Violle et al. 2007). In this respect, seed mass is an interesting trait for the

establishment phase of plant reproduction. Larger seeds store more resources, which are

therefore able to help young seedlings to survive and establish when there is low resources

(drought, deep shade) and high competition. Smaller seeds can be produced in larger numbers

with the same reproductive effort, and therefore raises the likelihood of establishment of a

seedling where competition is low and resource availably is high. (Cornelissen et al. 2003).

Limiting Similarity

The term limiting similarity was introduced by MacArthur & Levins (1967). This was work that

was based on Lotka-Volterra equations and MacArthur & Levins provided a mathematical

explanation in which they posited that “there is a limit to the similarity of competing species

which can coexist. The total number of species is proportional to the total range of the

environment divided by the niche breadth of the species” (MacArthur & Levins 1967). This

Master Thesis

8

early position was then more generalised away from single resource models, to be a term that

is applied to the relationship between some measure of the difference in the competitive

abilities of two competitors and the similarity in resource utilisation (Abrams 1983).

The use of the word limiting similarity in the context of assembly rules suggests that species

assemble within a community based on resource use functional traits, and that theys can more

readily coexist if they differ in their traits, such that competition is reduced (Götzenberger et

al. 2012) (Figure 2).

Figure 2: A graphical representation of the limiting similarity hypothesis depicting two invaders establishment success based on functional divergences with a native community (source:

http://bigsciencelittlesummaries.com/an-ecological-approach-to-invasion-resistance-insights-from-the-world-of-fashion/)

Limiting similarity is often termed trait divergence or moreover, trait divergence is seen as an

indicator of competition minimisation and an acting limiting similarity processes

(Götzenberger et al. 2012; Chalmandrier et al. 2013; Wilson 2007; Herben & Goldberg 2014;

Violle et al. 2011). The opposite, trait convergence is an abiotic process attributed to habitat

filtering, which filters for species with similarity in ecological (environmental) tolerances

(Gerhold et al. 2013; Götzenberger et al. 2012; May et al. 2013).

The aforementioned conceptual gradient between deterministic and stochastic processes is

typified through limiting similarity experimentation. Since its conceptualisation, the principle

of limiting similarity has been explored in many ways, often confirming its relevance (Wilson

& Stubbs 2012; Stubbs & Bastow Wilson 2004) or finding limited evidence of its relevance

(Thompson et al. 2010; Price & Pärtel 2013; Violle et al. 2011).

Master Thesis

9

Invasion by a Species

Species invasion of an environment is influenced by three factors: the number of propagules

entering, the characteristics of the new species (invasiveness) and susceptibility of the

environment to invasion (invasibility) (Davis et al. 2000). There is a central idea in invasion

theory that proposes that species-rich communities are less invasible (Lonsdale 1999). This is

an over simplistic view because species richness is a proxy for niche availability. Exotic species

respond to greater habitat diversity just like native species do (Lonsdale 1999). These

observations were made at community scale, Lonsdale (1999) does concede that at smaller

scales where plant competition operates there is no simplistic relationship based on native

richness which could predict invasibility. Generally speaking, invasibility of an environment is

dependent on climate, disturbance regime and competitive ability of the resident species

(Lonsdale 1999).

Resource partitioning and fluctuation could be the missing link in unifying sometimes

disagreeing theory on the invasibility of a community (Davis et al. 2000). The theory is that a

plant community becomes more susceptible to invasion whenever there is an increase in the

amount of unused resources. The assumptions are that the invading species must have access

to resources (e.g. light, nutrients and water) and that success of invasion will be increased if

the invader does not encounter intense competition for these resources from resident species

(see Limiting Similarity above). This is based on an established plant strategy model that states

that competition is less important in recently disturbed environments in which the resident

species are not likely to be using all available resources. Following from this, it can be said that

factors increasing the availability of limited resources will increase the invasibility of a

community (Davis et al. 2000). Davis et al. (2000) go further to suggest two basic ways that

resource availability could increase, namely; resource use of the native community can decline

(e.g. disturbance destroys the native vegetation, herbivory, etc.) or resource supply can

increase faster than the native vegetation can take it up (e.g. eutrophication, wet weather,

etc.). Once this periodic increase in unused resources has occurred, the community becomes

vulnerable to invasion. This theory was confirmed in a study looking at roadsides in California

where nutrient enrichment (eutrophication) was occurring and it was found that lowering the

nutrient levels through carbon addition also lowered the abundance of exotic species present

(Cleland et al. 2013).

Master Thesis

10

Chapter 2: The Glasshouse Experiment

Introduction

Changes in biodiversity have been more rapid over the past 50 years than at any other time in

human history, and the drivers for the changes that cause the biodiversity loss have either

stayed steady, showed no evidence for declining or are increasing in intensity (United Nations

Environmental Programme 2005). The most important direct drivers are land use changes

(conversion to cropland), invasive alien species, pollution and climate change (Secretariat of

the Convention on Biological Diversity 2010).

Grassland communities have been significantly depleted around the world due to their

favourable climatic conditions and soils, meaning that they preferentially are being converted

to croplands with low diversity (World Wildlife Fund, 2014, Lindenmayer & Burgman, 2005)().

Therefore, the ecological restoration of grasslands is becoming a priority for land managers

around the world wishing to address issues of biodiversity and habitat loss (Hobbs & Harris

2001).

Roadside verges offer a unique microcosm for plant establishment and growth. The majority

of roadside environments are preferably vegetated with grassland species. This is due to a

safety requirement for good visibility and reduced collision hazard. Roadside vegetation is

usually managed through regular mowing and significant herbicide application to control

undesirables (Quarles 2003). Roadsides environments can be characterised by high

temperatures and low humidity making seedling establishment difficult. The soils are usually

nitrogen enriched as a result of nitrogen emission from vehicle exhausts and thus offer high

nutrient levels which are favourable to IAS (Haan et al. 2012). Not only do roadsides provide

habitat for IAS, there exists a positive feedback loop, in that, roadsides receive higher seed

rain from non-native species from passing traffic, which are then able to establish easier (Haan

et al. 2012), these newly established individuals can then be further transported from the site

by passing traffic (Saunders & Hobbs 1991). Roadsides are important vectors of dispersal for

invasive species, and at the same time, hot spots for their development (Saunders & Hobbs

1991). A potential method to address this problem is to assemble roadside communities using

a limited similarity hypothesis to help these communities resist invasion by IAS (Funk & Cleland

2008).

Master Thesis

11

Limiting similarity hypothesis predicts that communities should be resistant to invasion by

non-native species if they present native species have similar functional traits (Funk & Cleland

2008). Having the same functional traits is translated into species competing for the same

finite resources using similar strategies, or another way of viewing it, there is a finite limit to

the niche-overlap that can occur in a given environment (MacArthur & Levins 1967).

Selecting the right functional trait for testing limiting similarity, when there is not information

on the soil seed bank of the roadside is challenging. Seed mass is a promising trait since it

influences the establishment and success of individual plants, but there exists a trade-off.

Firstly, seed mass is negatively correlated with number of seeds, that is, more seeds means

more chance some individuals may survive. Secondly, seed mass is positively correlated with

seedling survival in that larger seeds produce larger seedlings which are better able to

withstand low resources and environmental hazards (droughts, herbivory) (Smith & Fretwell

1974).

Another important aspect to consider in terms of resource based suppression is the increase

in resource availability commonly found in roadsides. The availability of soil nutrients, along

with water and light are the three basic requirements for plant growth (Raven et al. 2013). An

increase in soil nutrient levels will lead to increased biomass of the plants growing in it (Poorter

& Nagel 2000). On the other hand, for a native plant community, nutrient addition will

increase its vulnerability to invasion by alien species by increasing the amount unused

resources in the system (Davis et al. 2000).

We are interested to see the effects that soil nutrient addition will have during the

simultaneous establishment of a native community and Invasive species and how it affects the

competition parameters between the two.

We designed a greenhouse experiment to reduce the knowledge gap that exists with respect

to applying the limiting similarity hypothesis to guide optimal seed mix choices. Additionally,

we are interested to test if a limiting similarity exists in seed mass of establishing individuals

of IAS compared to the average seed mass of the native community it is competing with. It is

hoped the results from this experiment could be applied to future grassland restoration

projects. Hence, the aim of the study is to investigate the contribution plant seed size and soil

nutrient content have in affecting competitive success of invasive alien species in a

Master Thesis

12

greenhouse environment. Or conversely and more importantly for restoration ecology,

whether seed size is an adequate functional trait to be used to infer wether a native

community will show greater resistance to invasion from invasive alien species.

We hypothesize that: 1) Large-seeded native communities are more effective at supressing

the invasion success of small- and large-seeded invasive alien species; 2) Small-seeded native

communities are only effective at supressing the invasion of small-seeded invasive alien

species; 3) Nutrient enriched soils will increase the invasion success of all invasive alien species

within the small- and large-seeded native communities.

.

Master Thesis

13

Materials and Methods

Species Selection

Invasive Alien Species

Eight invasive alien plant species were selected in order to be seeded in native seed

communities. The small group included seeds under 0.5 mg and the large group those over 2

mg (Table 1). The experimental seed bank of these species was designed using average

values published for Ambrosia artemisiifolia and extrapolated for the other species for

better comparison (Rothrock et al. 1993; Fumanal et al. 2008)

Table 1: The chosen target invasive alien species were collected from the field (see Appendix 1 for locations)

Genus species Family Seed size group

Solidago gigantea Asteraceae Small

Solidago canadensis Asteraceae Small

Conyza canadensis Asteraceae Small

Erigeron annuus Asteraceae Small

Ambrosia artemisiifolia Asteraceae Large

Fallopia japonica Polygonaceae Large

Impatiens glandulifera Balsaminaceae Large

Heracleum mantegazzianum Apiaceae Large

Native Species

A pool of species with their corresponding traits was prepared, based on the roadside mixes

of the Rieger-Hofmann catalogue for Germany. The community composition was randomly

selected from this pool according to seed mass and life span for each replica, consisting of five

combinations of 5 native grassland species. The species were selected according to the mean

seed mass, including two species of grasses in both target community mixtures (Table 2). Two

levels were chosen for seed mass (i.e. small, large) and these were defined according to the

Master Thesis

14

0.25–0.75 percentile from the average seed mass of all species of the roadside seed mixture

(0.3 mg and 1.3 mg; Rieger-Hofmann GmbH)

Table 2: The native species chosen to make up the native community purchased from the commercial source

Genus species Family Seed Size Group

Achillea millefolium Asteraceae Small

Agrostis capillaris Poaceae Small

Origanum vulgare Lamiaceae Small

Papaver rhoeas Papaveraceae Small

Plantago media Plantanginaceae Small

Poa compressa Poaceae Small

Bromus erectus Poaceae Large

Centaurea cyanus Asteraceae Large

Centaurea scabiosa Asteraceae Large

Helictotrichon pubescens Poaceae Large

Knautia arvensis Dipsacaceae Large

Salvia pratensis Lamiaceae Large

Sanguisorba minor Rosaceae Large

Seed Preparation and Germination Trials

Invasive Species

Previous to the main experiment, all invasive species seeds were collected (see Appendix 1),

stratified when needed and tested for potential germination at ideal conditions. The amount

of 50 seeds were placed in Petri dishes, evenly distributed on filter papers (9 cm diameter)

moistened with de-ionized water and replicated five times. The stratification was carried at

4.5 °C and the period varied among the species (Table 3). After stratification, they were

placed into a climatic cabinet under day conditions for 16 hours (20 °C with artificial light)

and night conditions for 8 hours (12 °C; no light).

Master Thesis

15

Table 3: Time period required for stratification according to the species. This was defined as the period of time after more than 10% of the seeds started germination.

Species Stratification (4°C) Heracleum mantegazzianum 4 weeks

Fallopia japonica 3 weeks

Ambrosia artemisiifolia 3 weeks

Impatiens grandulifera 2 weeks

Erigeron annuus 4 weeks

Solidago gigantea No stratification needed

Solidago canadensis No stratification needed

Conyza canadensis No stratification needed

Seed were prepared for the main experiment by placing them in little biodegradable

transplanting pots for being stratified. The information on stratification requirements was

used later for the preparing the seeds for the main experiment

Emergence trials In order to avoid a density effect due to differences in emergence of the

native species, emergence trials were performed. These trials aimed to estimate the final

number of seed that had to be sown according to how each species performed. For this, 30

seeds from each native species were place on top of a 36 cm2 pot filled with low nutrient [pH

4.5-7.0; Conductivity 200 – 900 µS cm-1] potting soil (‘Einheits Erde Special’), replicated five

times and placed into a climatic chamber for germination. The trials were carried out initially

under day conditions for 12 hours (20 °C with artificial light) and night conditions for 8 hours

(10 °C; no light), but three weeks later was changed to day conditions for 16 hours (22 °C with

artificial light) and night conditions for 8 hours (10 °C; no light).

Experimental Design

The greenhouse experiment was established in the Centre of Greenhouses and Laboratories

Dürnast, part of the Life Science Centre Weihenstephan, Technische Universität München in

Munich, Germany. Following from recommendations by Snaydon (1991) an additive

experimental design was chosen in order to investigate the competitive ability of the IAS

Master Thesis

16

target species. This way, the density of the target species in the pure stands (controls) was the

same as the density of the target species in the mixtures (‘treatments’). The experiment ran

for 8 weeks (from mid-May until early July) in an unheated greenhouse which had a

temperature of 22 ± 3 °C (mean ± SD).

The experiment had a randomised factorial block design. Eight IAS were planted within

different native plant communities, this being the first factor, made up of two levels, large

seeded and small seeded native community (small with average mass <0.5 mg and large-

seeded mix > 1.9 mg). The next factor was nutrient addition and was made up of two levels,

nutrient addition or none. The nutrient addition consisted of the addition of 10 ml at a 1.5‰

concentration of fertilizer Ferty 3 (15% N, 10% P2O5, 15% K2O) to each pot (3 l). The treatments

were then replicated five times to make a total of 160 pots. Controls were also implemented

whereby the eight Invasive alien species were subjected to only nutrient additions without

the native community influence and the native communities experienced nutrient addition

treatment without the presence of invasive species (Figure 3).

Figure 3: The experimental design of the study. Eight invasive plant species are subjected to influences from two types of native community based on seed size. The impact of nutrient addition is also tested. Controls are used to compare performance of species subject to the treatments with respect to no treatment. (Illustration: M. Brockard and H. Vogt)

Master Thesis

17

This design allows for the observation of the competitive effect that large and small seeded

native communities impose on establishment by large and small seeded IAS and whether

nutrient levels also exert an effect on the establishment success.

The exact mixtures were randomised (Appendix 2), with the ratio of seeds present in each

kept constant. The seeding density was kept constant at 15 g m-2. This density was chosen to

keep results comparable between a preliminary experiment (F. Yanelli, unpubl. work) and

this experiment. The seed producer recommends a seeding density of 3 g m-2 (Kiehl et al.

2010), as we had five times more soil volume than the previous experiment but overall

smaller surface, we have in fact created high density communities. In order to achieve this

constant density, the average seed mass was calculated for the native seeds (2.18 mg). It

was calculated that approximately 213 seeds were required per pot. As we were using five

species per pot, this equated to 43 seeds per species per pot. Using the germination data

obtained before experiment begin, we were able to adjust the seed count required, relative

to the germination rate per species as shown in Table 4.

Table 4: Depicting the germination rates that were obtained from germination tests prior to

experiment begin. These rates were then used to adjust the amount of seeds used per species to

keep the density of the native species in the community’s constant at 15 g m-2.

Genus species Seed size Germination rate (%) Total seeds

Bromus erectus Large 80 52

Centaurea cyanus Large 83 51

Centaurea scabiosa Large 78 53

Helictotrichon pubescens Large 41 69

Knautia arvensis Large 88 48

Salvia pratensis Large 46 66

Sanguisorba minor Large 80 52

Achilliea millefolium Small 90 48

Agrostis capillaris Small 68 57

Origanum vulgare Small 65 58

Master Thesis

18

Papaver rhoeas Small 56 62

Plantago media Small 58 61

Poa compressa Small 65 58

Potting up of the experiment involved filling 20 cm diameter pots with low nutrient potting

soil (‘Einheits Erde Special’). Initially, an empty 200 ml plastic cup was left empty in the

centre of the pots to create a void in the soil. The same 200 ml plastic cups were filled

separately. The filled pots and cups were then brought into the greenhouse and randomly

distributed onto one of the tables. These were left for 1 week to be watered in and allow the

soil to settle. Extra soil was added to individual pots and cups that required more soil so that

soil amount was kept constant. Further on, each of the 200 ml plastic cups was sown with

one invasive species seeds and left to germinate. At the same time, native species mixes

were evenly sown into the larger pots. After 4 weeks, the invasive species that were alive

and developed first true leaves were then translocated into the respective pots (Appendix

3). In effect within each 20 cm diameter pot, one seedling of the Invasive species was

surrounded by a native community made up of either small or large seeded members (Figure

4).

Figure 4: The distribution of the native communities in each pot. Placed in the middle of the community in treatment pots was the invasive alien species. In control pots, either the native community or the invasive alien species was not present. (Image source: Florencia Yannelli)

Master Thesis

19

After set-up, the pots were separated across two tables within the greenhouse. One table

would receive the nutrient treatments and the other table would not receive nutrient

treatments, for preventing the non-nutrient addition treatments to be affected when

watering. In order to control for edge effects and micro climatic conditions, the pots were

redistributed within their respective tables once per month. The pots were initially watered

every day from above until germination and establishment of the plants, then changed to

watering every second day from beneath allowing the pots to soak for 1 hour.

Master Thesis

20

Variables and Measurement

The response variables that were measured are summarised in the following table:

Variable Description

TOTAL BIOMASS Total above ground dried mass

IAS LEAVES MASS Combined leaves dried mass

IAS STEMS MASS Combined stems dried mass

IAS SPECIFIC LEAF AREA Ratio of Leaf area to dry mass

IAS HEIGHT Height to apical meristem

The chosen plant characteristics are considered acceptable ways of measuring plant

responses to soil resources, response to disturbance, plant defence/protection and

competitive strength (Cornelissen et al. 2003). Specific leaf area was measured using the

approach as per the Cornelissen paper. Directly removing three healthy leaves (including

petiole) and scanning them into the computer software ImageJ for precise area

measurements (courtesy; Wayne Rasband, Research Services Branch, National Institute of

Mental Health, Bethesda, Maryland, USA.) Moreover, the drying procedure was to take all

collected material and place it into an oven at 75 oC for a minimum of 48 hours.

Data Analysis

The relative competition index (RCI) was used to estimate the competitive effect of native

species on the invasive species, with the following formula (Weigelt & Jolliffe 2003):

RCIγ = γControl − γTreatment

γControl

Using this formula, a particular variable is measured in the controls, i.e. biomass, and it is

compared to the value an individual gains under treatment conditions, making direct

comparison of competitive performance achievable

Master Thesis

21

The RCI was calculated for all response variables measured i.e. native biomass, invasive total

biomass, leaves biomass, steams biomass, SLA and height. Subsequently, RCI and row values

were tested for normality using the modified Shapiro-Wilk test (Rahman & Govindarajulu

1997). Only Ambrosia artemisiifolia provided normally distributed data across all but one

variable (RCI-SLA). As the assumption for normal distribution failed across the majority of

species, it was decided that in order to make comparisons using all species, only non-

parametric testing would be applied. Therefore, the effects of the treatments were verified

using the non-parametric Kruskal-Wallis test (Kruskal & Wallis 1952) to explore multi-factor

interactions and Wilcoxon test for pairwise comparison across the two factors, seed size and

nutrient addition. Each invasive species was analysed separately, but then all small and large

seeded IAS were grouped together to seek for general results on the effect of limiting

similarity in terms of the seed size.

All statistical analysis were performed using Infostat software (Di-Rienzo et al. 2013).

Master Thesis

22

Results

From the initially decided upon eight species of IAS, there was no data collected for Conyza

canadensis, Fallopia japonica, Heracleum mantegazzianum and Impatiens glandulifera.

There are two reasons for this omission: First, Heracleum mantegazzianum, Impatiens

glandulifera, and Conyza canadensis did not germinate adequate to fulfil the requirements

for all replicates required, this means that these species were removed before beginning and

transfer of these species into the native species communities did not occur. Second,

although Fallopia japonica did show adequate germination to fulfil the replicates

requirement; this species experienced during the course of the experiment for unknown

reasons an excessive rate of mortality and so there were not enough individuals left to be

statistically valid. Hence, I show results only for three small-seeded species (Solidago

Canadensis, Solidago gigantea and Erigeron annuus) and one large-seeded species

(Ambrosia artemisiifolia).

Species-specific results

There was no significant effect of either seed size of the native community or nutrient

addition on Solidago canadensis (p > 0.05). On the other hand, Solidago gigantea produced

observable differences in RCI-Native Biomass (H = 7.9, p = 0.048) for both factors seed mass

and nutrient addition. Wilcoxon tests showed that the statistical difference for the relative

competition index in native biomass was a result of the nutrient addition treatment. RCI-

native biomass was lower in no nutrient additions (mean = -0.13) when compared to

nutrient addition treatments (mean = 0.15; W = 121, p = 0.011).

In Erigeron annus differences were observed in the RCI-leaf area (H = 9.63, p = 0.022).

Further, pairwise testing with the nutrient factor using Wilcoxon tests did not produce any

significant difference. There was however a statistical difference observed in the RCI-leaf

area (LSM mean 0.93, SSM mean 0.76, [W = 94, p = 0.0025]), RCI-leaf mass (LSM mean 0.95,

SSM mean 0.77, [W= 90, p=0.0084]) and RCI-height (LSM mean 0.71, SSM mean 0.51, [W=

86.5, p=0.0217]).

Master Thesis

23

In terms of the only large-seeded invasive species Ambrosisa artemisiifolia, multifactor

comparisons testing did not indicate any observable differences between the treatments.

Wilcoxon pairwise comparisons on nutrient addition indicated a significant difference in

relative competition index of SLA (W = 71, p = 0.010). No nutrient addition treatments

produced lower competition indexes (mean = -0.12) than the nutrient additions (mean =

0.13). Seed mass of the native community was not found to be significant in terms of each

of the five measured variables.

Biomass of all invasive species was lower in all treatments when compared to the controls,

this is reflected in the relative competition index value for all treatments across all species

being above one [suppression] (Figures 5–8). There was no statistical difference between the

factors nutrient addition and native community seed size (both, p > 0.05).

Figure 5: Relative competition index for Solidago canadensis biomass showing similar levels of suppression across all treatments. (Lsm= Large seeded community; Ssm= Small seeded community; No-nut is no nutrient additions; Nut= Nutrient additions)

Master Thesis

24

Figure 6: Relative competition index for Solidago gigantea biomass showing similar levels of suppression across all treatments. (Lsm= Large seeded community; Ssm= Small seeded community; No-nut is no nutrient additions; Nut= Nutrient additions)

Figure 7: Relative competition index for Erigeron annuus biomass showing similar levels of suppression across all treatments. (Lsm= Large seeded community; Ssm= Small seeded community; No-nut is no nutrient additions; Nut= Nutrient additions)

Master Thesis

25

Figure 8: Relative competition index for Ambrosia artemisiifolia biomass showing similar levels of suppression across all treatments. (Lsm= Large seeded community; Ssm= Small seeded community; No-nut is no nutrient additions; Nut= Nutrient additions)

Combined Results

Nutrient additions did not significantly affect any of the measured response variables for

either the large or small IAS (W = 3415.5; p > 0.05). The total biomass of all invasive species

tested was significantly lower in both the large- and small-seeded communities when both

are compared to the control treatments (p < 0.0001) (Figure 9).

Master Thesis

26

Figure 9: Large and small seed communities were indistinguishable in their ability to reduce the total biomass of both large and small seeded invasive alien species when compared to the control treatments (p < 0.0001).

Master Thesis

27

Discussion

Specifically the results indicate that regardless of seed size, with no nutrient addition the

native communities produced more biomass in the treatments where Solidago gigantea was

present. The opposite was true for the nutrient addition treatments, in this case the native

communities produced more biomass in the treatments where Solidago gigantea was not

present. Leaf area of Erigeron annus was least supressed in the small seeded communities

with nutrient addition.

The results of the experiment indicate that none of the three postulated hypotheses could be

accepted. Native communities made up of large seed mixes were not more effective at

supressing the invasion success of either small or large seeded invasive alien species when

compared to the supressing effect exerted by small seeded native communities. Furthermore,

nutrient enrichment in this experiment did not indicate that the invasion success of alien

species was increased in either large or small seeded communities. A limiting similarity

between native community seed size and IAS seed size was not observed. An important point

to note however, is that a true comparison between effects on large- and small-seeded

invasive alien species could not be determined with the experiment as it only was left with

one large-seeded species (Ambrosia artemisiifolia) for the comparison.

A result which was a little less anticipated was seen where the small-seeded mixes supressed

the biomass of the invasive alien species equally as well as the large-seeded mixes. This result,

although disproving our hypothesis on limiting similarity of seed size, does however indicate

the role interspecific competition plays in community dynamics. In all cases, the invasive

species produced significantly more biomass in the control pots where no native community

was present. This can only be explained by the absence of the community competing for

resources with the IAS (Aerts 1999). An interesting addition to explore this result next time

may be to include measurement of below ground characteristics as they have been shown to

be stronger (Aerts 1999)(Casper & Jackson 1997). Also following this, the rather symmetrical

effects observed between the two treatments for seed size in this experiment also correlate

with results from other studies that have shown that the effects of belowground competition

act more symmetrically when compared to above ground competition effects (Casper &

Jackson 1997).

Master Thesis

28

Another explanation for the suppression affected by both large- and small-seeded

communities could also be linked in to the seeding density that was used for the experiment.

We had chosen 15 g m-2 which was approximately five times the recommended density from

the seed supplier. Higher density, which ties in with the idea of reducing the spatial resources

available to invading species may be the key driver for the suppression ability of newly

established plant communities in this experiment. This was the finding of an experiment in

which a doubling of the recommended seeding rate of wheat plants lead to a halving of weedy

species present in the crop (Lemerle et al. 2004)

Interestingly, the nutrient additions in this experiment did not induce a biomass increase in

either the IAS or the native communities present. This is contrary to previous work in this area

suggesting that nutrient increases should lead to an increase in biomass (Poorter & Nagel

2000). A possible explanation for this is that the soil used for the experiment was already over

abundant in nutrients relative to what the plants required. In essence, even the treatments

that were considered no nutrient additions actually were abundant with unused resources,

creating a situation where nutrient availability was not a limiting resource, even in the no

nutrient treatments. This would tie in with a secondary point, in that an increase in limiting

resource’s should increase that invasibility of a native community (Davis et al. 2000) and this

was not observed with our data.

Conclusion

Our results although not allowing us to accept our original hypotheses, do provide important

results that can be adopted by land managers tasked with restoring grassland communities.

Owing to the effect we observed that small seeded mixes supressed invasive species equally

as well as large seeded communities. This suggested that density has a very important role.

Land managers who need to purchase seed do so by weight. It would be the logical choice for

them, based on our results to purchase a mix that includes smaller seeded species, as for the

same weight of seed they will end up with more individuals and therefore, a higher plant

density for a lower cost.

Master Thesis

29

Chapter 3: Final Discussion and Conclusion

The damage caused by invasive species are one of the most significant challenges that land

managers and restoration ecologists will have to deal with leading into the future (Hobbs &

Harris 2001). The invasion of exotic species poses a two folded problem, not only do they

contribute to environmental degradation, they also substantially impede efforts to restore

ecosystems (Funk & Cleland 2008).

Regardless of the causes for degradation, effective restoration and management will require

increased levels of understanding of the processes and properties of ecosystems that convey

resistance and resilience from invasive alien species (Falk et al. 2006). In essence, in the case

of de novo establishment of a grassland communities in roadsides it is imperative to recreate

communities with these processes and properties (Saunders & Hobbs 1991). The task for

ecologists is to integrate and obtain relevant ecological information and test these approaches

through continued experimentation.

Integrated weed management is the deliberate selection, integration and implementation of

effective weed control measures with due consideration of economic, ecological and

sociological consequences (Hobbs & Humphries 1995). In using an integrated weed

management approach the first step in actually preventing the infestation is the designing of

roadside communities based on properties that convey resilience. This is where sound

ecological understanding in areas such as succession, assembly rules, functional traits and

limiting similarity theory play a vital role (Walker et al. 2007).

A central principle in integrated weed management is the idea of an economic threshold

(Figure 10) (Swanton & Weise 1991). Prior to reaching this threshold, natural weed controlling

methods should be manipulated to their fullest. Once this threshold has been reached action

in the form of chemical control must be taken in order to prevent an outbreak of a pest species

before it can cause an economic injury (Swanton & Weise 1991). The term economic injury

implies that after breaking a certain threshold, the cost to eradicate the invading population

becomes exponentially more than the preventative actions (Harker & O’Donovan 2013).

Integrated weed management sustainable management practices such cultural controls that

maintain pests at low levels. This keeps pesticide use to a minimum by using them only in an

outbreak situation (Harker & O’Donovan 2013).

Master Thesis

30

Figure 10: The figure illustrates the principle of the economic threshold and is based on a logistical growth curve. (Image source: http://www.weedcenter.org/textbook/8_jacobs_options.html)

Roadsides are a hotspot for the development of IAS infestations as a result of high seed rain

and favourable environmental conditions for their growth (Haan et al. 2012). The dispersal

vector of passing vehicles cannot be controlled. It is therefore inevitable that there will be

some level of infestation of invasive alien species present even in the most well planned

restored roadside sites. Coupled with sound ecology theory, integrated weed management is

a sustainable management choice for invasive alien species in roadside grassland

communities.

Ecological theory, and the significant research that supports it is a solid foundation for devising

management and restoration methods that will create or maintain sustainable ecosystems

(Clewell et al. 2004). Adding to the theoretical suite of options available to restoration

ecologists is the theory of limiting similarity (Funk & Cleland 2008). Our experimentation did

indicate that seed mass is an inappropriate functional trait for use in a limiting similarity

approach. Therefore the experimentation is still a step forward for scientific understanding

and the integration of limiting similarity theory into sustainable management strategies and

practical restoration techniques.

Master Thesis

31

Acknowledgements

I wish to extend my utmost gratitude to Florencia Yanelli for her limitless knowledge, support

and guidance throughout the experimental and writing stage of this thesis work and not giving

up on me. I wish to thank the staff at Dürnast Research Laboratory and Greenhouse for their

technical guidance and support. Thank you to Martina Brockard and Hannah Vogt for assisting

in establishing the experiment. Lastly I wish to thank Prof. Dr. Johannes Kollmann for accepting

my thesis proposal and providing me with his expert knowledge, technical guidance and the

chairs resources to fulfil the thesis requirements.

Master Thesis

32

References

Abrams, P., 1983. The theory of limiting similarity. Annual review of ecology and systematics, (34). Available at: http://www.jstor.org/stable/2096978 [Accessed March 29, 2014].

Aerts, R., 1999. Interspecific competition in natural plant communities: mechanisms, trade-offs and plant-soil feedbacks. Journal of Experimental Botany, (January 1999). Available at: http://jxb.oxfordjournals.org/content/50/330/29.short [Accessed December 15, 2014].

De Bello, F., 2012. The quest for trait convergence and divergence in community assembly: are null-models the magic wand? Global Ecology and Biogeography, 21(3), pp.312–317. Available at: http://doi.wiley.com/10.1111/j.1466-8238.2011.00682.x [Accessed July 12, 2014].

Casper, B.B. & Jackson, R.B., 1997. Plant Competition Underground. Annual Review of Ecology and Systematics, 28(1), pp.545–570. Available at: http://arjournals.annualreviews.org/doi/abs/10.1146%2Fannurev.ecolsys.28.1.545.

Chalmandrier, L. et al., 2013. A family of null models to distinguish between environmental filtering and biotic interactions in functional diversity patterns. Journal of vegetation science : official organ of the International Association for Vegetation Science, 24(5), pp.853–864. Available at: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=4003529&tool=pmcentrez&rendertype=abstract [Accessed August 1, 2014].

Cleland, E.E., Larios, L. & Suding, K.N., 2013. Strengthening Invasion Filters to Reassemble Native Plant Communities: Soil Resources and Phenological Overlap. Restoration Ecology, 21(3), pp.390–398. Available at: http://doi.wiley.com/10.1111/j.1526-100X.2012.00896.x [Accessed March 28, 2014].

Clewell, A., Aronson, J. & Winterhalder, K., 2004. The SER International primer on ecological restoration. , 2(2), pp.206–207. Available at: http://scholar.google.com/scholar?hl=en&btnG=Search&q=intitle:The+SER+International+Primer+o+n+Ecological+Restoration+O+verview#1 [Accessed October 22, 2014].

Cody, M.L. & Diamond, J.M., 1975. Ecology and Evolution of Communities, Belknap Press of Harvard University Press. Available at: http://books.google.de/books?id=j_idbVxwzpQC.

Connor, E. & Simberloff, D., 1979. The assembly of species communities: chance or competition? Ecology, 60(6), pp.1132–1140. Available at: http://www.jstor.org/stable/1936961 [Accessed November 7, 2014].

Cornelissen, J.H.C. et al., 2003. A handbook of protocols for standardised and easy measurement of plant functional traits worldwide. Australian Journal of Botany, 51(4), p.335. Available at: http://www.publish.csiro.au/?paper=BT02124.

Costanza, R. et al., 2014. Changes in the global value of ecosystem services. Global Environmental Change, 26(0), pp.152–158. Available at: http://www.sciencedirect.com/science/article/pii/S0959378014000685.

Davis, M., Grime, J. & Thompson, K., 2000. Fluctuating resources in plant communities: a general theory of invasibility. Journal of Ecology, pp.528–534. Available at:

Master Thesis

33

http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2745.2000.00473.x/full [Accessed November 15, 2014].

Falk, D.A. et al., 2006. Foundations of Restoration Ecology, Society for Ecological Restoration International.

Fumanal, B., Gaudot, I. & Bretagnolle, F., 2008. Seed-bank dynamics in the invasive plant, Ambrosia artemisiifolia L. Seed Science Research, 18(02), pp.101–114. Available at: http://journals.cambridge.org/article_S0960258508974316.

Funk, J. & Cleland, E., 2008. Restoration through reassembly: plant traits and invasion resistance. Trends in Ecology & …, 23(12), pp.695–703. Available at: http://www.ncbi.nlm.nih.gov/pubmed/18951652 [Accessed March 29, 2014].

Gerhold, P. et al., 2013. Functional and phylogenetic community assembly linked to changes in species diversity in a long-term resource manipulation experiment F. de Bello, ed. Journal of Vegetation Science, 24(5), pp.843–852. Available at: http://doi.wiley.com/10.1111/jvs.12052 [Accessed March 25, 2014].

Götzenberger, L. et al., 2012. Ecological assembly rules in plant communities--approaches, patterns and prospects. Biological reviews of the Cambridge Philosophical Society, 87(1), pp.111–27. Available at: http://www.ncbi.nlm.nih.gov/pubmed/21692965 [Accessed March 24, 2014].

Grube, A. et al., 2011. Pesticides Industry Sales and Usage 2006 and 2007 Market Estimates, Washington DC.

Haan, N.L., Hunter, M.R. & Hunter, M.D., 2012. Investigating Predictors of Plant Establishment During Roadside Restoration. Restoration Ecology, 20(3), pp.315–321. Available at: http://dx.doi.org/10.1111/j.1526-100X.2011.00802.x.

Harker, K.N. & O’Donovan, J.T., 2013. Recent Weed Control, Weed Management, and Integrated Weed Management. Weed Technology, 27(1), pp.1–11. Available at: http://dx.doi.org/10.1614/WT-D-12-00109.1.

Herben, T. & Goldberg, D.E., 2014. Community assembly by limiting similarity vs. competitive hierarchies: testing the consequences of dispersion of individual traits A. MacDougall, ed. Journal of Ecology, 102(1), pp.156–166. Available at: http://doi.wiley.com/10.1111/1365-2745.12181 [Accessed March 25, 2014].

Hobbs, R.J. & Harris, J. a., 2001. Restoration Ecology: Repairing the Earth’s Ecosystems in the New Millennium. Restoration Ecology, 9(2), pp.239–246. Available at: http://doi.wiley.com/10.1046/j.1526-100x.2001.009002239.x.

Hobbs, R.J. & Humphries, S.E., 1995. An integrated approach to the ecology and management of plant invasions. Conservation Biology, 9(4), pp.761–770.

Keddy, P.A., 1992. Assembly and response rules: two goals for predictive community ecology. Journal of Vegetation Science, 3(2), pp.157–164. Available at: http://dx.doi.org/10.2307/3235676.

Kembel, S.W., 2009. Disentangling niche and neutral influences on community assembly: assessing the performance of community phylogenetic structure tests. Ecology letters, 12(9), pp.949–60. Available at: http://www.ncbi.nlm.nih.gov/pubmed/19702749 [Accessed March 19, 2014].

Master Thesis

34

Kiehl, K. et al., 2010. Species introduction in restoration projects – Evaluation of different techniques for the establishment of semi-natural grasslands in Central and Northwestern Europe. Basic and Applied Ecology, 11(4), pp.285–299. Available at: http://www.sciencedirect.com/science/article/pii/S1439179109001455.

Kruskal, W.H. & Wallis, W.A., 1952. Use of Ranks in One-Criterion Variance Analysis. Journal of the American Statistical Association, 47(260), pp.583–621. Available at: http://www.tandfonline.com/doi/abs/10.1080/01621459.1952.10483441.

Laliberté, E., Norton, D. a. & Scott, D., 2013. Contrasting effects of productivity and disturbance on plant functional diversity at local and metacommunity scales N. Mason, ed. Journal of Vegetation Science, 24(5), pp.834–842. Available at: http://doi.wiley.com/10.1111/jvs.12044 [Accessed March 28, 2014].

Laughlin, D.C., 2014. Applying trait-based models to achieve functional targets for theory-driven ecological restoration. Ecology letters, 17(7), pp.771–84. Available at: http://www.ncbi.nlm.nih.gov/pubmed/24766299 [Accessed July 9, 2014].

Lemerle, D. et al., 2004. Reliability of higher seeding rates of wheat for increased competitiveness with weeds in low rainfall environments. The Journal of Agricultural Science, 142(4), pp.395–409. Available at: http://www.journals.cambridge.org/abstract_S002185960400454X [Accessed December 15, 2014].

Lindenmayer, D. & Burgman, M., 2005. Vegetation loss and degradation. In Practical Conservation Biology. CSIRO Publishing.

Lonsdale, W., 1999. Global patterns of plant invasions and the concept of invasibility. Ecology, 80(5), pp.1522–1536. Available at: http://www.esajournals.org/doi/abs/10.1890/0012-9658(1999)080%5B1522:GPOPIA%5D2.0.CO%3B2 [Accessed November 15, 2014].

MacArthur, R. & Levins, R., 1967. The limiting similarity, convergence, and divergence of coexisting species. American naturalist, 101(921), pp.377–385. Available at: http://www.jstor.org/stable/2459090 [Accessed October 22, 2014].

May, F. et al., 2013. Plant functional traits and community assembly along interacting gradients of productivity and fragmentation. Perspectives in Plant Ecology, Evolution and Systematics, 15(6), pp.304–318. Available at: http://linkinghub.elsevier.com/retrieve/pii/S1433831913000590 [Accessed March 28, 2014].

Mouchet, M. a. et al., 2010. Functional diversity measures: an overview of their redundancy and their ability to discriminate community assembly rules. Functional Ecology, 24(4), pp.867–876. Available at: http://doi.wiley.com/10.1111/j.1365-2435.2010.01695.x [Accessed March 20, 2014].

Philipp Schledorn, M.K., 2014. Detection of Glyphosate Residues in Animals and Humans. Journal of Environmental & Analytical Toxicology, 04(02). Available at: http://www.omicsonline.org/open-access/detection-of-glyphosate-residues-in-animals-and-humans-2161-0525.1000210.php?aid=23853 [Accessed October 31, 2014].

Poggio, S.L., 2005. Structure of weed communities occurring in monoculture and intercropping of field pea and barley. Agriculture, Ecosystems & Environment, 109(1-2), pp.48–58. Available at:

Master Thesis

35

http://linkinghub.elsevier.com/retrieve/pii/S0167880905001180 [Accessed November 15, 2014].

Poorter, H. & Nagel, O., 2000. The role of biomass allocation in the growth response of plants to different levels of light, CO2, nutrients and water: a quantitative review. Functional Plant Biology, 27(12), p.1191. Available at: http://www.publish.csiro.au/paper/PP99173_CO.

Price, J. & Pärtel, M., 2013. Can limiting similarity increase invasion resistance? A meta‐analysis of experimental studies. Oikos, 122(5), pp.649–656. Available at: http://doi.wiley.com/10.1111/j.1600-0706.2012.00121.x [Accessed March 29, 2014].

Quarles, W., 2003. Native Plants and Integrated Roadside Vegetaion Management. IPM Practitioner, XXV(3).

Rahman, M.M. & Govindarajulu, Z., 1997. A modification of the test of Shapiro and Wilk for normality. Journal of Applied Statistics, 24(2), pp.219–236. Available at: http://dx.doi.org/10.1080/02664769723828.

Raven, P.H., Evert, R.F. & Eichhorn, S.E., 2013. Biology of Plants, W.H. Freeman Publishers. Available at: http://books.google.de/books?id=6MjduQAACAAJ.

Rothrock, P.E., Squiers, E.R. & Sheeley, S., 1993. Heterogeneity and Size of a Persistent Seedbank of Ambrosia artemisiifolia L. and Setaria faberi Herrm. Bulletin of the Torrey Botanical Club, 120(4), pp.417–422. Available at: http://www.jstor.org/stable/2996745.

Saunders, D.A. & Hobbs, R.J., 1991. Roads, Roadsides and Wildlife Conservation: A Review. In NATURE CONSERVATION 2: THE ROLE OF CORRIDORS. Chipping Norton, N.S.W.: Surrey Beatty & Sons, pp. 99–117.

Secretariat of the Convention on Biological Diversity, 2010. Global Biodiversity Outlook 3, Montreal. Available at: www.cbd.int/GBO3.

Smith, C.C. & Fretwell, S.D., 1974. The Optimal Balance Between Size and Number of Offspring. AMERICAN NATURALIST, 108(962), pp.499–506.

Snaydon, R.W., 1991. Replacement or Additive Designs for Competition Studies? The Journal of Applied Ecology, 28(3), p.930. Available at: <Go to ISI>://A1991HA12300013\nhttp://www.jstor.org/stable/2404218?origin=crossref.

Stubbs, W.J. & Bastow Wilson, J., 2004. Evidence for limiting similarity in a sand dune community. Journal of Ecology, 92(4), pp.557–567. Available at: http://doi.wiley.com/10.1111/j.0022-0477.2004.00898.x.

Swanton, C.J. & Weise, S.F., 1991. Integrated Weed Management: The Rationale and Approach. Weed Technology, 5(3), pp.657–663. Available at: http://www.jstor.org/stable/3987055\nhttp://www.jstor.org.ezproxy.sussex.ac.uk/stable/pdfplus/3987055.pdf?acceptTC=true.

Temperton, V.M. et al., 2013. Assembly Rules and Restoration Ecology: Bridging the Gap Between Theory and Practice, Island Press.

Master Thesis

36

Thompson, K. et al., 2010. Little evidence for limiting similarity in a long-term study of a roadside plant community. Journal of Ecology, 98(2), pp.480–487. Available at: http://doi.wiley.com/10.1111/j.1365-2745.2009.01610.x [Accessed March 25, 2014].

United Nations Environmental Programme, 2005. Millenium Ecosystem Assesment, Washington DC.

Violle, C. et al., 2007. Let the concept of trait be functional! Oikos, 116(5), pp.882–892. Available at: http://dx.doi.org/10.1111/j.0030-1299.2007.15559.x.

Violle, C. et al., 2011. Phylogenetic limiting similarity and competitive exclusion. Ecology letters, 14(8), pp.782–7. Available at: http://www.ncbi.nlm.nih.gov/pubmed/21672121 [Accessed March 19, 2014].

Walker, L.R., Walker, J. & Hobbs, R.J., 2007. Linking Restoration and Ecological Succession, Springer. Available at: http://books.google.de/books?id=RYZUe7I7BZcC.

Weigelt, A. & Jolliffe, P., 2003. Indices of plant competition. Journal of Ecology, 91(5), pp.707–720. Available at: http://doi.wiley.com/10.1046/j.1365-2745.2003.00805.x.

Weiher, E., Clarke, G. & Keddy, P., 1998. Community assembly rules, morphological dispersion, and the coexistence of plant species. Oikos, 81, pp.309–322. Available at: http://www.jstor.org/stable/3547051 [Accessed November 1, 2014].

Weiher, E. & Keddy, P., 1995. Assembly rules, null models, and trait dispersion: new questions from old patterns. Oikos, 74(1), pp.159–164. Available at: http://www.jstor.org/stable/3545686 [Accessed November 7, 2014].

Wilson, J., 2007. Trait-divergence assembly rules have been demonstrated: Limiting similarity lives! A reply to Grime. Journal of Vegetation Science, (1974), pp.451–452. Available at: http://onlinelibrary.wiley.com/doi/10.1111/j.1654-1103.2007.tb02557.x/abstract [Accessed April 21, 2014].

Wilson, J.B. & Stubbs, W.J., 2012. Evidence for assembly rules: limiting similarity within a saltmarsh. Journal of Ecology, 100(1), pp.210–221. Available at: http://doi.wiley.com/10.1111/j.1365-2745.2011.01891.x [Accessed March 27, 2014].

World Wildlife Fund, 2014. Living Planet Report 2014 R. McLellan, ed.,

Young, T., Chase, J. & Huddleston, R., 2001. Community succession and assembly comparing, contrasting and combining paradigms in the context of ecological restoration. Ecological restoration, pp.5–18. Available at: http://er.uwpress.org/content/19/1/5.full.pdf [Accessed November 7, 2014].

Master Thesis

37

Appendices

1. Seed Collection Locations

SPECIES LOCATION SOLIDAGO GIGANTEA

River Isar at Freising (coordinates: 48.400951, 11.757429) -> 7 whole ramets were collected in 7 patches separated by at least

100m (February 2014).

SOLIDAGO CANADENSIS North of Freising (48.412119, 11.739362) & Marienhof

(48.291204, 11.689709) -> 6-7 ramets were collected from around 4-5 patches from each site (October 2013).

CONYZA CANADENSIS

Seed were acquired from Herbiseed (from Serbia) -> I don't have specific info on this species because we bought the seeds.

ERIGERON ANNUUS

TUM Weihenstephan (48.399546, 11.719602) & Marienhof (48.291204, 11.689709) -> more than 50 flowers collected at

each location (October 2013).

IMPATIENS GLANDULIFERA Isar close to Neufahrn (48.312114, 11.700218), Freising - Votting (48.395274, 11.713096), Talham (48.478938, 11.774057) ->seeds

collected from 3-4 fruits per plant from around 5 plants per patch, moved 50m and collected the same amount and so on

(October 2013).

H. MANTEGAZZIANUM

A place close to Hohenkammer (48.403167, 11.536919). All the available seeds collected from 5 individuals in only one patch

(October 2013).

AMBROSIA ARTEMISIIFOLIA

Seeds were collected in a mud-deposit location at 'Neue Donau' in Austria (48°16'38.47"N 16°22'2.55"E). Date of harvest:

12.10.2012

FALLOPIA JAPONICA

Seeds were collected in Freising from only one patch and several ramets (48°23'52.2"N 11°44'54.1"E). Data harvest: October 2013

Master Thesis

38

2. Exact Seed Mixtures per Replicate

Large seeded Small seeded

R1 R1

Bromus erectus Poa compressa

Helictotrichon pubescens Agrostis capillaris

Centaurea cyanus Achillea millefolium

Salvia pratensis Origanum vulgare

Sanguisorba minor Papaver rhoeas

R2 R2

Bromus erectus Poa compressa

Helictotrichon pubescens Agrostis capillaris

Centaurea cyanus Papaver rhoeas

Knautia arvensis Plantago media

Salvia pratensis Achillea millefolium

R3 R3

Bromus erectus Poa compressa

Helictotrichon pubescens Agrostis capillaris

Salvia pratensis Achillea millefolium

Sanguisorba minor Papaver rhoeas

Knautia arvensis Plantago media

R4 R4

Bromus erectus Poa compressa

Helictotrichon pubescens Agrostis capillaris

Sanguisorba minor Achillea millefolium

Knautia arvensis Papaver rhoeas

Master Thesis

39

Centaurea scabiosa Plantago media

R5 R5

Bromus erectus Poa compressa

Helictotrichon pubescens Agrostis capillaris

Salvia pratensis Papaver rhoeas

Centaurea scabiosa Plantago media

Sanguisorba minor Origanum vulgare

3. The exact timing of the various stages of the experimental set-up.

Date Process

April 2014 Stratification and Germination Trials

05. – 13. May 2014 Native Community Preparation

12. May Potting up (Pots and Cups)

19. May Sowing of Seed (Pots and Cups)

9. June Transplanting of IAS into final pots