Species Interactions

What is a species fundamental niche?

The full set of environmental conditions and resources under which an organisms could survive and reproduce in the absence of competitors, predators, or pathogens

How does a realised niche differ from the fundamental niche?

Realised niche is the subset actually occupied when biotic interactions restricts a species distribution and abundance

State the competitive exclusion principle

If 2 species compete for exactly the same limiting resource under constant conditions, the superior competitor will eventually exclude the others

In the Lotka-Volterra competition model, what does negative interaction coefficient α12​< 0 signify?

Species 2 inhibits the per-capita growth of Species 1(Interspecific competition)

List all five two-species interaction types by the signs of s12​ and s21​

-Competition (-,-)

-Mutualism (+,+)

-Predation/Parasitism (-,+) or (+,-)

-Commensalism (0,+) or (+,0)

-Amensalism (0,-) or (-,0)

Write the zero-growth isocline equations for Lotka-Volterra competition

dN₁/dt=0:N₁+α₁₂N₂=K₁

dN₂/dt=0:α₂₁N₁+N₂=K₂

What are the four possible outcomes in the Lotka-Volterra competition plane?

-Species 1 excludes 2

-Species 2 excludes 1

-Unstable coexistence (biostability; outcome depends on initial densities)

-Stable coexistence (interior equilibrium is stable)

How can you tell from the isocline slopes whether coexistence will be stable?

Occurs if each species inhibits itself more than it inhibits the other

-Intraspecific effect is steeper than the interspecific effect

Define phase space

A plot with species 1 density on the x-axis and Species 2 density on the y-axis, where vector arrows show instantaneous directions

-dN₁/dt or dN₂/dt

What do trajectories in phase space represent?

The paths traced over time, showing how populations approach equilibria or exclusion points

Describe Type I functional response

A linear increase of per-predator consumption with prey density

-f(R)=aR

-Filter feeders

What distinguishes a Type II functional response?

A saturating (hyperbolic) curve due to handling time

-f(R)=aR/1+aT_hR

-T_h is the time spent processing each prey item

Sketch the key features of a Type III functional response.

-A sigmoid curve

-Low consumption at low prey density

-Accelerating uptake

f(R)=aR^h/1+aT_hR^h , h>1

What is commensalism in the two-species interactions framework?

One species benefits (+) while the other is unaffected (0)

-Interaction signs (+,0) or (0,+)

Define amensalism

One species is harmed (-) while other is unaffected (0)

-Signs (-,0) or (0,-)