Chapter 28-30a

Keystone Species + Biodiversity

Why did the wolf population stop growing before the elk population increased?

• Riparian areas (near creek) saplings grew back quicker than open upland areas which had little to no recovery

Landscape of Fear

Prey animals change their behavior across space depending on how risky each area feels due to predators

• Predators can have big impact even without actually decreasing herbivore populations

Keystone Species

Species that have an effect disproportionately large for their abundance

• High Impact

• Low Biomass

• Often top predators but not always

• Loss of species has large consequences

• Competitive Exclusion

Dominant Species

Species that is very abundant/high biomass which leads to a big effect

• High Impact

• High Biomass

Ecosystem Engineers

Species that modify the habitat

Keystone Herbivores (Example)

Large herbivores converts woodlands into savannas in Africa

• Elephants

Ecological Network Theory

Use the same mathematical tools use for “complex systems” to analyze structure and function of foods webs

Species-Area Relationship

Smaller areas/islands harbor fewer species

What changes as you add area?

• # of niches

• Food chain length

• Presence of keystone species

• Inclusion of rare species

Species Area Relationship Arrhenius Equation

• S = cA^z

• log S = z*logA + logc

  • S = # of species

  • A = Island Area

  • c = baseline species richness

  • z = slope/how quickly species richness increases with area

Species-Distance Relationship

Closer areas/islands harbor more species

What islands are species richness most strongly related to island area?

Far islands

• Immigration is low so area is strongest predictor of species richness

What comes with farther distance?

• Reduce probability of dispersal

• Fewer animals, plants, seeds can reach distant island

• Near islands = high immigration rates + higher equilibrium species richness

Equilibrium Model of Island Biogeography

Number of species occurring on island represents a balance b/t immigration and extinction

• Large + Near Islands = High Species Richness

• Small + Far Islands = Low Species Richness

Why does predicted rate of extinction rise with increasing # of species on an island?

• Larger pool of possible extinctions

• Number of species increase = population size of each decrease

• Number of species increase = more potential for competitive interactions b/t species increase

Theory of Island Biogeography

# species on an island = [# NEW species that immigrate] - [# species that go extinct]

• S = equilibrium # of species on island

What are extinction curves for small and large islands?

• Small island extinction curve = Bigger/Speeds Up

• Large island extinction curve = Smaller/Slows Down

Why does increasing island size slow down extinction rate?

• Increased population size

• Increase habitat diversity

• Reduce competition

Species Turnover

Extinction replaced with new immigrant

Simberloff Island Area and Species Richness Effect

Reduced area means…

• Species richness reduced

• Lost species

• Area has positive influence on species richness

• Predict # of species not which species

What are the hypotheses for why biodiversity hotspots are in the tropics?

• More productivity

• Most consistent environment

• More complex habitat

• Geometric constraints (falsified)

• More land area

More Productivity Hypothesis/Energy Diversity Hypothesis

• More Direct Radiation from Sun + More Water = More primary producers = More trophic levels can be supported

• High PET = more species

More Consistent Environment Hypothesis/Cradle or Museum

Stable environment = More species coexistence

• Cradle = Higher speciation/origination rates

• Museum = Lower extinction rates

• Tropics are both cradle and museum

More Complex Habitat Hypothesis

More niche + More species

• More vertical layers

• More microhabitats

• More plant diversity

Geometric Constraints Hypothesis

Species ranges overlap more near equator simply because of geometry

• Falsified

More Land Area Hypothesis

Species-Area Relationship

• Most continuous land area of all latitude ranges

• More area = more species

What are the causes of biodiversity?

• Dispersal/Immigration Level - Amount of area + Distance from other areas

• Abiotic Factors Level - Climate + Disturbance

• Species Interaction Level - Competition + Predation + Herbivory + Parasitism + Mutualism