Day 6 Community Ecology and Species Interactions

Biological communities

set of interacting species that live within a particular area

Communities defined by

their species richness

Produces similar communities

similar environmental conditions

Species interactions

1. competition

2. consumption

3. mutualism

4. commensalism

Competition

different species use the same resource (-, -)

Consumption

on species eats, or absorbs nutrients from another (+, -)

Mutualism

species interactions are mutually beneficial (+,+)

Commensalism

one species benefit, with no effect on the other (+, 0)

Species interactions affect

distribution and abundance of species

Species interactions result in

evolution because species act as agents of natural selection when they interact

Competition results from

interactions to obtain resource in short supply

1. prey items

2. nutrients

3. water

4. light

5. space

Negative outcomes of competition

1. less growth

2. shorter life span

3. reduced reproduction

Ecological niche

all environmental conditions required by a species for its existance

Abiotic factors

1. temperature

2. humidity

3. rainfall

4. light levels

5. soil composition

6. refuge/shelter

Niche equivalent examples

American bison and African gnu

American agave and African aloe

Simplifies niche

one species niche without competition

Asymmetric competition

one species experiences a greater fitness decline than the other

Symmetric competition

species experience the same amount of fitness decline

Proposed competitive exclusion

G. F. Gause

Competitive exclusion

two species with identical niches cannot coexist

if competition is asymmetric, the weak competitor can be driven to extinction

Realized niche

portion of niche used when competitors are present 

Fundamental niche

niche seen when there is no competitors present

Character displacement

a change in species trait(s) that allows exploitation of different resources

Character displacement can result in

niche differentiation

Niche differentiation

an evolutionary change in resource use

• also called niche partioning

Map of niche differentiation - on canvas

Types of consumption

1. herbivory

2. parasitism

3. predation

4. fungivory

Herbivory

consume plant tissue

Parasitism

consume nutrients from a host

Predation

predator kills and consumes all or most of prey

Fungivory

fungus tissues are consumed

Adaptions for defense

1. constitutive defense

2. inducible defense

Constitutive defense

always present

Inducible defense

produced only in response to a consumer

Coevolutionary arms race

1. consumers evolve traits that increase their efficiency in prey capture

2. consumed evolve traits that make them unpalatable or elusive

3. selection on consumers for traits that counter consumed species adaptations

4. and so on, repeats

Case study of arms race

rough skinned newts and garter snakes

Tetrodoxin (TTX)

blocks voltage gated NA+ channels in neurons

Mutualism between bull horn acacia and ants

acacias provide shelter and food for ants

ants provide protection for acacias

Mutualism between ants and treehoppers

treehoppers provide honeydew for ants

ants protect treehoppers from jumping spiders

Commensalism between ant birds and army ants

ants stir up insects while hunting - ant birds tag along to eat those insects

• ants get no benefit or harm from ant birds