Community interactions: the niche concept and symbiotic relationships

Any species has a well defined

habitat• ‘its address’• Where it can live• What it needs to eat• Breeding grounds• Water requirements• etc etc

• HABITATS ARE DEFINED AND CONSTANT

Any population of that species

has a well defined niche• ‘its occupation’• The species it interacts with• The species it depends on• The species that depend on

it…• NICHES CAN GROW AND

SHRINK, DEPENDING ON ‘EXTERNAL’ FACTORS

The area where an organism lives is

called its habitat.

A habitat includes both biotic and abiotic factors

Habitat

‘Nicher’ (French): to NestA term describing the way of life of a populationNo two species can occupy the same niche in the same ecosystemTo describe a population’s niche, you need to describe its ‘specialised habitat’:

– space and territory– Nutrition and feeding habits– Interactions with other organisms– Its reproductive habits– Its role in the community

The Niche concept: A Working Analogy

In 1927, Charles Sutherland Elton, the British Ecologist, stated: ‘When an ecologist states ‘There goes a badger’, he should include in his thoughts a definite idea of the animal’s role in the community, just as if he had said ‘There goes the vicar’

Defining a Niche : ‘The Boundary conditions’

• Two species that use exactly the same resources cannot occupy the same niche

• Only one species or population can occupy the same niche for an extended period

A population has a fundamental AND a realised niche

Fundamental Niche

A species’ fundamental niche is the full range of environmental and social conditions under which it

could potentially survive and reproduce‘potential niche’

• Some species have a broad fundamental niche• Some species have a narrow fundamental niche

Species with a broad niche

• ‘Generalists’• Widely distributed

geographically• Adaptable

Species with a narrow Niche• ‘Specialists’

• Not adaptable• Under threat of extinction if the niche changes

Realised Niche

The realised niche is the specific set of conditions in which it survives in a given habitat or ecosystem, given the other species or limitations present.These are the conditions to which the population is best adapted.

‘Realised Niche’ is not a constant for a species

• In fact, populations of the same species may occupy different realised niches within different ecosystems

• It all depends on the other species and environmental factors involved in ‘sharing of the resources’

What interactions occur within communities?

All community interactions play an essential role in survival of both species

Essential Interactions

PredationParasitismMutualism

(Commensalism)Competition

Any ‘long term’ relationship in which two species live closely together is called symbiosis.

Symbiotic relationships include: • mutualism• commensalism • parasitism• (predation)

Symbiosis

‘Symbiotic’ relationship 1: Predation

Predation

An interaction in which one organism captures and feeds on another organism is called predation.

The organism that does the killing and eating is called the predator, and the food organism is the prey.

Parasitism: one organism (the parasite) lives on or inside another organism (the host) and harms it.

• yuk.....!• The parasite of the day Blog...

Community Interactions

Mutualism: both species benefit from the relationship.

Commensalism: one member of the association benefits and the other is neither helped nor harmed.

Symbiotic relationships can take place between species from different kingdoms!

• Symbiosis• Mutualism, Commensalism and parasitism• Sunfish and seagulls...• Fish Cleaners• Giving Fish a bath• Clownfish and anemones

CompetitionCompetition occurs when organisms of the same or

different species attempt to use an ecological resource in the same place at the same time.

A resource is any necessity of life, such as water, nutrients, light, food, or space.

Direct competition in nature often results in a winner and a loser—with the losing organism failing to survive.

The principle of competitive exclusion

Aka ‘Gause’s Law’

‘No two species can occupy the same niche in the same habitat

for a prolonged time’

The Competitive Exclusion Principle

• The best adapted species will survive

• The loser will struggle to survive and reproduce, and will eventually become extinct OR migrate (if its niche is broad enough)

Examples are abundant• Invasive species• Red versus Grey

Squirrel in Western Europe

• Gause’s Paramecium

Competitive Exclusion and Invasive species…

Invasive Species are those which have been introduced to a non-native habitat/ecosystem (usually by human interention). They often out-compete – (and drive towards extinction) – the native species…• Grey Squirrels• Cane toads!• Zebra Mussels

Competitive Exclusion: Squirrels

Competitive Exclusion: Squirrel Distribution

Competition in the plant world

• Japanese knotweed• David Attenborough tropical conpetition

Competition can even take place between species from different kingdoms…

• Spider versus plant

Can species ‘work around’ the competitive exclusion principle?

Yes they can!: Niche Partitioning

As there is a limited about of space and resources on Earth, organisms can use niche partitioning1. Spatial: Two different species use the same resource by occupying different areas within the range of the resource2. Temporal: Two species eliminate direct competition by using the same resource at different times

Spatial Niche Partitioning

Closely related bird species

occupy different foraging locations

on a single tree species

Community Interactions

The distribution of these warblers avoids direct competition, because each species feeds in a different part of the tree.

Yellow-Rumped Warbler

Bay-Breasted Warbler

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Cape May Warbler

Temporal Niche Partitioning

Different species of spiny mouse inhabiting the same ecosystem may be either nocturnal OR diurnal feeders