Chapter 5 Community Processes: Species Interactions & Succession © Brooks/Cole Publishing Company /...

Chapter 5 Chapter 5

Community Processes: Community Processes: Species Interactions & Species Interactions &

SuccessionSuccession

© Brooks/Cole Publishing Company / ITP

Outline 5Outline 51. The Ecological Niche

roles, fundamental & realized niche, generalists vs. specialists

2. Some General Types of Speciesnative, non–native, indicator, & keystone species

3. Types of Species Interactions4. Competition & Predation

principle of competitive exclusion, predator–prey relations

5. Symbiotic Species Interactionsparasitism, mutualism, & commensalism


Outline 5Outline 56. Characteristics of Populations

size, density, dispersion, age structure, dynamics

7. Population Dynamics & Carrying Capacitygrowth limits, exponential vs. logistic growth, carrying capacity

8. Reproductive Strategies & Survivalr– vs. K–strategists; survivorship curves

9. Successionprimary & secondary succession

10. Island Biogeography11. Stability & Sustainability


• Realized niche

• Resources

• Specialist

• Conditions

• Generalist

• Fundamental niche

• all the physical attributes of the environment

• parts of the environment used by an organism.

• the full niche of a spp. that could be used.

• the portion of the niche that is actually used by a spp.

• Species with broad niche• Species with narrow

niche

1. 1. The Ecological Niche

• niche:

• conditions

• resources:

• habitat,

• the many physical attributes of the environment, though not consumed, that influence biological processes & population growth, e.g., temperature, salinity, acidity;

• the role that an organism plays in an ecosystem, defined by the range of conditions & resources within which an organism can live;

• the actual place an organism lives. • substances or parts of the environment

used by an organism & consumed or otherwise made unavailable to other organisms , e.g., food, water, & nesting sites for animals; water, nutrients, & solar radiation for plants;

Fundamental vs. Realized Niche• fundamental niche: the full range of conditions &

resources that an organism could theoretically use in the absence of competition with other species.

• realized niche: the portion of the fundamental niche that an organism actually occupies; actual range of conditions & resources that an organism uses.

• niche overlap between species leads to competition;

• competition causes organisms to not be able to occupy the full fundamental niche;

Generalists vs. Specialists• generalists have broad

niches,

• examples of generalists: cockroaches, coyotes, dandelions, humans;

• generalists may have advantage when environmental conditions change (e.g., weedy species such as dandelions in disturbed habitat);

• specialists have narrow niches:

• examples of specialists: spotted owls, which require old–growth forests in the Pacific Northwest; giant pandas, which eat primarily bamboo in bamboo forests of China;

• whereas specialists may have advantage when environmental conditions are more constant (e.g., many species of tropical rain forest).

Types of Species – Indicator SpeciesTypes of Species – Indicator Species

• indicator species: species that serve as early warnings that a community or ecosystem is being damaged:

• example: decline of migratory songbirds in North America indicates loss & fragmentation of habitat in mesoAmerica & South America;

• example: presence of trout in mountain streams is an indicator of good water quality;

• example: presence of spotted owls is indicator of healthy old–growth forest.

Types of Species – Keystone SpeciesTypes of Species – Keystone Species

• keystone species: species that play a critical role in an ecosystem:

• example: sea otters are keystone species because they prevent sea urchins from depleting kelp beds;

• example: dung beetles are keystone species because they remove, bury, & recycle animal waste;

• example: beavers are keystone species because they build dams & create habitat for a diverse community of species (bluegill fish, muskrats, herons, ducks…).

• "The loss of a keystone species is like a drill accidentally striking a power line. It causes lights to go out all over." –– E.O. Wilson

3. Types of Species Interactions3. Types of Species Interactions• major types of biotic interactions:• interspecific competition: when two or more

species use the same limited resource (food, space, etc.) and adversely affect each other

• example: fire ants and native species of ants in North America; fire ants sharply are better competitors & sharply reduce populations of up to 90% of native species.

• predation: members of one species (predator) feed on another species (prey);

• example: lion feeding on gazelle.

Types of Species InteractionsTypes of Species Interactions• major types of biotic interactions (continued):• symbiosis: a long–lasting relationship in which

species live together in intimate association:• parasitism: one organism (parasite) lives on part of

another organism (host), e.g., flea living on a dog• mutualism: two species interacting in a way that

benefits both, e.g., lichens consist of algae & fungi that benefit each other (in this example can't live apart);

• commensalism: one organism benefits from another, but neither helps nor harm that other organism, e.g., epiphyte growing on a tree (epiphyte benefits & tree not effected, unless there are many epiphytes).

4. Competition & Predation4. Competition & Predation

• Interspecific competion results because of niche overlap = overlap in requirements for limited resources.

• Types of Competition:• interference competition: one species limits

another species' access to a resource; e.g., hummingbirds defending feeding territories.

• exploitation competition: competing species both have access to a limited resource, but one exploits the resource more quickly or efficiently.

Principle of Competitive ExclusionPrinciple of Competitive Exclusion

G.P. Gausse, in a classical experiment (1934), showed that two species with identical niches can not coexist indefinitely.

This is called the principle of competitive exclusion. Note that when grown together, Paramecium aurelia outcompetes Paramecium caudatum.

Resource PartitioningResource Partitioning

Species with similar resource requirements can coexist because they use limited resources at different times, in different ways, or in different places.

For example, specialized feeding niches of various birds of coastal wetland enable coexistence of many species.



Fig. 9–5

Five species of insect–eating warblers are able to coexist in spruce forest of Maine. Each species minimizes competition with others for food by spending at least half its feeding time in a distinct portion of spruce trees (shaded areas); each also consumes somewhat different insect species.



Fig. 9–5 (continued)

Character DisplacementCharacter Displacement

Over many years coexisting species with similar niches tend to evolve physical & behavioral adaptations to minimize competition.

For example on islands where they co–ocurr, species of Darwin's finch have evolved different bill sizes & eat different size prey.

Predators & Prey Predators & Prey What features characterize them?What features characterize them?

Predators tend to evolve characteristics for efficient capture of prey (keen eyesight, speed, etc.).

Prey tend to evolve chacteristics to avoid being eaten (camoflauge, chemical defenses, behaviors that startle predators, etc.).

5. Symbiotic Species Interactions5. Symbiotic Species Interactions• Parasitism can be viewed as a special type of predation

wherein the parasite:• 1) is usually smaller than the prey,• 2) remains closely associated with the prey over time, &• 3) rarely kills its host.• Endoparasites • live inside their host, e.g., tapeworm living in the gut of a

mammal; plasmodium living inside a vertebrate & causing malaria.

• Ectoparasites • live outside their host, e.g., mosquito feeding on the blood

of mammal; lamprey attaching to outside of a host fish (see Fig. 9–13).

MutualismMutualism• Mutualism involves a relationship in which two

interacting species benefit.• obligatory mutualism results when two organisms can

not live without each other;• example: in lichens an algae provides photosynthesis & a

fungi provides a home for the algae;• example: Rhizobium bacteria, in legume plant root

nodules, fix nitrogen & legume provides carbohydrates & home;

• example: termites have gut organism that can digest cellulose.

• In other mutualisms the organisms can live apart, but there is strong mutual benefit in the relationship;

• example: flowering plants & their pollinators, plant gets pollinated, pollinator gets nectar or pollen to eat;

MutualismMutualism


There are many more classic examples of mutualism.

example: oxpeckers, a type of bird, feeds on the parasitic tics of various large mammals in Africa, such as the black rhinoceros (see Fig. 9–14);

example: mycorrhizal fungi live in the roots of various plants; the fungus gets carbohydrates & the plant gets better absorption of nutrients by the fungal mat that extends beyond the roots (see Fig. 9–15);

example: the clownfish in the coral reefs of Australia lives among the tentacles of sea anemones; the clownfish gains protection from the stinging tentacles & food scraps when the anemone feeds; the anemone gains protection from various fish that feed on sea anemones (see Fig. 9–16);

example: certain species of stinging ants live in acacias; the ants get a home and food in the form of nectar; the acacias get protection from various herbivores.

CommensalismCommensalism


Commensalism involves a symbiotic relationship in which one species beneifits while another is neither helped not harmed to a significant degree.

example: redwood sorrel, a small herbaceous plant, benefits from growing in the shade of tall redwoods, but the redwoods are not affected;

example: epiphytes (such as orchids & bromeliads) that grow on trunk & branches of trees in the tropical rain forest gain a favorable place to live; whereas, at least when epiphytes are not overly abundant, the tree is not affected (see Fig. 9–17).

Note that if epiphytes become sufficiently abundant to block light, the tree can be negatively affected, and this becomes an example of competition.

1. Characteristics of Populations• population

dynamics

• population size

• population density

• Dispersion

• age structure

• . is the number of individuals in a population at a given time;

• is the number of individuals per unit area in terrestrial ecosystems or per unit volume in aquatic ecosystems;

• is the proportion of individuals in each age group (e.g., prereproductive, reproductive, & postreproductive) of a population.

• is the spatial patterning individuals;• Changes in population size, density,

dispersion, & age distribution are known as

Characteristics of Populations


What is the difference between clumped, uniform & random dispersion?

Fig. 10–2

2. Population Dynamics & Carrying Capacity

• Population size is governed by births, deaths, immigration, and emigration:

• [Population Change] = • [Births + Immigration] – [Deaths + Emigration]• If the number of individuals added by births &

immigration are balanced by those lost by deaths & emigration then there is zero population growth;

• populations vary in their capacity for growth, also known as biotic potential;

• the intrinsic rate of growth (r) is the rate at which a population will grow if it had unlimited resources.

Population Dynamics


What are the most important factors that tend to increase or decrease population size?

Fig. 10–3

Carrying Capacity

• There are always limits to population growth in nature.

• carrying capacity (K) is the number of individuals that can be sustained in a given space;

• the concept of carrying capacity is of central importance in environmental science;

• if the carrying capacity for an organism is exceeded, resources are depleted, environmental degradation results, & the population declines.

Exponential vs. Logistic Growth• What’s the difference

between Exponential & Logistic Growth?

• Exponential growth occurs when resources are not limiting.

• Logistic growth occurs when resources become more and more limiting as population size increases.

Exponential Population Growth• Exponential growth occurs

when resources are not limiting.

• during exponential growth population size increases faster & faster with time;

• currently the human population is undergoing exponential growth;

• exponential growth can not occur forever because eventually some factor limits population growth.

Logistic Population Growth

• Logistic population growth occurs when the population growth rate decreases as the population size increases.

• note that when the population is small the logistic population growth curve looks like exponential growth;

• over time, the population size approaches a carrying capacity (K).

Exceeding the Carrying CapacityDuring the mid–1800s sheep populations exceeded the carrying capacity

of the island of Tasmania. This "overshoot" was followed by a "population crash". Numbers then stabilized, with oscillation about the carrying capacity.

Exceeding the Carrying CapacityReindeer introduced to a small island off of Alaska in the

early 1900s exceeded the carrying capacity, with an "overshoot" followed by a "population crash" in which the population was totally decimated by the mid–1900s.

Population Curves in NatureNatural populations display a broad diversity of population curves. Stable

populations are relatively constant over time.

Cyclic curves are often associated with seasons or fluctuating resource availability.

Irruptive curves are characteristic of species that only have high numbers for only brief periods of times (e.g., seven–year cicada).

Population Curves in Nature Population cycles for the snowshoe hare & Canadian lynx

are believed to result because the hares periodically deplete their food, leading to first a crash of the hare population & then a crash of the lynx population.

3. Reproductive Strategies & Survival

• Organisms can be divided into two categories of "strategies" for reproduction & survival:

• r–strategist species, • tend to live in recently disturbed (early

successional) environments where resources are not limiting; such species tend to have high intrinsic rates of growth (high r);

• K–strategist species• tend to live in environments where resources are

limiting (later succession) & tend to have lower intrinsic rates of growth and characteristics that enable them to live near their carry capacity (population size near K).

r–Strategist Species

Characteristics of r–strategists, including production of many small & unprotected young, enable these species to live in places where resources are temporarily abundant.

These species are typically "weedy" or opportunistic.

K–Strategist SpeciesCharacteristics of

K–strategists, including production of few large & well cared for young, enable these species to live in places where resources are limited.

These species are typically good competitors.

Survivorship Curves• Three kinds of

curves:• late loss (usually

K–strategists), in which high mortality is late in life;

• constant loss (such as songbirds), in which mortality is about the same for any age;

• early loss (usually r–strategists), in which high mortality is early in life.

6. Succession6. Succession


succession: gradual & fairly predictable change in species composition with time.

•some species colonize & become more abundant;

•other species decline or even disappear.

two kinds of succession:

•primary succession involves the gradual establishment of biotic communiites in an area where no life existed before;

•secondary succession involves the gradual reestablishment of biotic communiites in an area where a biotic community was previously present.

Primary SuccessionPrimary Succession


Primary succession occurs with time in lifeless areas.

•examples include succession newly formed islands & succession after the retreat of a glacier;

•typically lichens & mosses first colonize bare rock;

•latter small herbs & shrubs colonize;

•finally tree species colonize;

•the first species to colonize are termed pioneer species;

•the progression of species that colonize with time are commonly termed early, mid, & late successional species.



Generalized physical appearance showing the types, relative sizes, and stratification of plant species in various terrestrial communities or ecosystems.

Fig. 9–18



Primary succession over several hundred years on bare rock exposed by a retreating glacier on Isle Royal in northern Lake Superior.

Fig. 9–19



Greatly simplified view of primary succession in a newly created pond in a temperate area. Nutrient rich bottom sediment is shown in dark brown.

Fig. 9–20a



Fig. 9–20 b, c, & d

Secondary SuccessionSecondary Succession


Secondary succession occurs where the natural community of organisms has been disturbed, removed, or destroyed.

•example: "old field succession" in eastern North America, where agricultural fields go through succession from herbaceous plants, to shrubs & early successional trees, to mid–successional forest, to oak–hickory forest;

•according to the classic view, succession proceeds until an area is occupied by a climax community, however recent views recognize that succession is influenced by variability & chaotic events such that a single climax is not predictable.



Secondary succession over 150–200 years in an abandoned farm field in North Carolina.

Fig. 9–21



Successional changes in the animal community accompany successional changes in the plant community.

Fig. 9–22

DisturbanceDisturbance


What is the role of disturbance in succession?

• disturbance: a discrete event that disrupts an ecosystem or community;

• examples of natural disturbance: fires, hurricanes, tornadoes, droughts, & floods;

• examples of human–caused disturbance: deforestation, overgrazing, plowing;

• disturbance initiates secondary succession by eliminating part or all of the existing community, & by changing conditions & releasing resources.

Mechanisms of SuccessionMechanisms of Succession


Both primary & secondary succession are driven by three mechanisms:

• facilitiation: a process by which an earlier successional species makes the environment suitable for latter successional species; e.g., legumes fixing nitrogen can enable later successional species;

• inhibition: a process whereby one species hinders the establishment & growth of other species; e.g., shade of late successional trees inhibits the growth of early successional trees;

• tolerance: a process whereby later successional species are unaffected by earlier successional species.

Changes During SuccessionChanges During Succession


During succession species diversity & stratification tend to increase, while growth rates & primary productivity tend to decrease.

Fig. 9–23

Ecosystem Changes During SuccessionEcosystem Changes During Succession


Characteristic Early Succession Late SuccessionPlant size small largeSpecies diversity low highTrophic structure mostly producers mixture of producers,

consumers, &decomposers

Ecological niches few, moregeneralized

many, morespecialized

Communityorganization (# links)

low high

Biomass low highNet PrimaryProductivity

high low

Food web simple complexEfficiency for nutrientcycling

low high

Efficiency of energyuse

low high

7. Island Biogeography7. Island Biogeography


In the species equilibrium model of island biogeography (developed by Robert MacArthur & Edward O. Wilson) the number of species on an island is determined by the balance between immigration & extinction.

Fig. 9–24

Island BiogeographyIsland Biogeography


Small islands are expected to have lower immigration rates & higher extinction rates, & hence less species than large islands.

Fig. 9–24



Far islands are expected to have lower immigration rates, & hence less species than near islands.

Fig. 9–24



The model of island biogeography has been widely applied in conservation biology by viewing the landscape as composed of habitat islands separated by an ocean of degraded or unsuitable habitat modified by human activity.

• large habitat patches tend to have more species;

• habitat patches that are near larger intact habitat areas tend to have more species;

• these principles can be applied to land preservation & management efforts.

8. Stability & Sustainability8. Stability & Sustainability


Stability has three aspects:• inertia (or persistence): the ability of a system to resist

being disturbed or altered;• constancy: the abilty of a living system to maintain a

certain size or state;• resilience: the ability of a living system to recover after a

disturbance;

Signs of poor health or stressed ecosystems:• decrease in primary productivity;• increased nutrient losses;• decline or extinction of indicator species;• increased populations of pests or disease organisms;• decline in species diversity;• presence of contaminants.

Through an understanding of ecology we can grapple with what it means to have sustainable ecosystems.

Chapter 5 Community Processes: Species Interactions & Succession © Brooks/Cole Publishing Company /...

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