BIOL204-M3L15

Community

all of the populations of different species that interact in a certain area

+, -, 0 meaning

fitness benefit, fitness cost, neutral affect on fitness

Types of interactions

commensalism, competition, consumption, mutualism

Commensalism

when one species benefits but the other species is unaffected (+/0)

• very conditional

Competition

when individuals use the same resources, resulting in lower fitness for both (-/-)

Consumption

when one organism eats/ absorbs nutrients or resources from another living organism, increasing fitness of consumer and decreasing fitness of victim (+/-)

Mutualism

when both species interact in a way that benefits both’s fitness (+/+)

• context dependent—Ex. coral

Intraspecific competition

competition within species

Interspecific competition

competition between different species

• can be direct: physical interference

• or indirect: depletion of shared resources

Key features of species interactions

• affect distribution and abundance of a species

• act as agents of natural selection when they interact

• Are dynamic & context dependent

Complete niche overlap

competitive exclusion: 2 species that occupy the exact same niche cannot coexist one will outcompete the other

Partial niche overlap

both species may persist but stronger species will reduce the weaker species realized niche

Niche differentiation

evolutionary change in resource use caused by competition (behavioral)

• natural selection favors individuals that compete less

Character displacement

evolutionary change that occurs in species traits that enables species to exploit different resources (physical)

• Ex. Galapagos finches beak depth

Commensalism orchid Ex.

orchids on trees for sunlight, no affect on tree but high density of orchids can change this

Why does competition result in lower fitness for both?

because the cost of competition is time and energy which they could be using this on growth and reproduction instead

3 types of consumption/ trophic interactions

1. predation: predator kills and consumes all or most of the prey, usually carnivores

2. herbivory: a herbivore consumes plant and algal tissues like leaves, stems, fruits, but not usually entire organism

3. parasitism: an organism that lives on or in a host and takes resources from it

Coevolutionary arms race

as species evolve one species will be evolving to what's more fit, and then the other species will also evolve to counteract that; species are evolving to outdo each other

Constitutive defenses

traits that are always present Ex. thorns

Inducible defenses

induced in response to a threat (physical, chemical, or behavioral defensive traits)

Parasite-host interactions (transmission)

Ex. ants become parasitized by nematodes and make their bottoms look like berries to be plucked by birds, decreasing the ants fitness, and then the nematodes are transmitted through birds feces and consumed by ants again

Are mutualists altruistic?

NO, they are not doing it to benefit other species, rather their doing it for their own fitness benefit

Attributes of a community structure

1. Total number of species

2. Relative abundance of species 

3. Network of interactions of species 

4. Physical structure of the environment (abiotic & biotic factors)

Species richness

counting number of species present in a community

Species diversity

incorporating richness and evenness (relative abundance)

Foodwebs

overlapping food chains showing consumption interactions

• arrow goes towards the organism getting the energy

Trophic levels

• producers, primary, secondary, tertiary, quaternary consumers

• Biomass decrease while moving up trophic levels

Keystone species

organisms that exert a disproportionately large, crucial influence on their ecosystem's structure and biodiversity relative to their abundance

Starfish Ex. keystone species

Trophic cascade + Wolf & Aspen tree Ex.

when changes in top-down control (consumers) cause indirect effects 2 or 3 links away in a food web

Ecosystem engineers

physical structures Ex. coral

Disturbance

 any strong, short-lived disruption to a community that changes the distribution of living or nonliving resources

• Ex. forest fires, windstorms, floods, disease epidemics

Disturbance regime

long-term, cumulative patterns of disruptive events

Succession

development of communities after disturbance

Primary succession

when a disturbance removes the soil and its organisms and organisms that live above the soil surface 

• initiated by glaciers, floods, volcanic eruptions, landslides

Secondary succession

when disturbance removes some or all of the organisms from an area but leaves the soil  

Resistance

community experiences a small or large change in terms of biomass/diversity

Resilience

community recovers slowly or quickly

Draw resistance and resilience graph

Successional pathway

 sequence of a species that appears over time

Early successional and late successional communities

• Early successional communities: dominated by short lived species that are small in stature and disperse their seeds, larvae, etc. Across far distances 

• Late successional communities (climax): dominated by species that are long lived, large, and good competitors

Species interactions during succession

facilitation, tolerance, inhibition

Facilitation

presence of early-arriving species makes conditions more favorable for later arriving species; not altruistic Ex. providing nutrients

Tolerance

existing species have no effect on probability that subsequent species will become established

Inhibition

when presence of one species inhibits establishment/ growth of another 

Equilibrium

when immigration and extinction interact, an equilibrium occurs–a balance between arrival of new species and extinction of existing ones–if a disturbance changes richness immigration and extinction should restore equilibrium

What happens to extinction and immigration rates as richness increases?

• extinction increases, as there’s more competition

• immigration declines — prevented by competition of already existing species

Area effect

larger area supports more species

Why more species are near the equator (tropics) than the poles

• Stable climate which is less harsh with consistent conditions

• Larger spatial area

• Higher energy available (sunlight and rain)

• Tropics are oldest–long amount of evolutionary time 

Larger islands close to mainland vs. Smaller islands far from mainland

• Larger islands close to mainland have higher immigration rates due to closer access by immigrants and extinction rates are highest on small islands far away due to less resources and immigrants have harder access 

• Species richness is higher on larger and near shore islands

Impact on abundance by each species interaction