Lecture 19: Community Ecology Flashcards
intraspecific competition
competition within a species between members of said species (among conspecifics) ex. population running out of food because there are too many individuals
interspecific competition
competition between species (among heterospecifics)
Lotka-Volterra Equations
models two species competing (outgrowth of the logistic equation)
competition
negative effects for both species
predation
benefits predator, hurts the prey
mutualism
beneficial for both
exploitative competition
Also known as scramble competition, two species do not need to interact directly or even be active at the same time to compete. If one consumes a resource leaving less for the other, they are competing (squirrel eating bird seed).
Interference competition
also known as contest competition, it is a direct interaction between species, for example territory battles (ants fighting).
Are invasive species superior competitors?
Yes, usually their impact on native species is greater than the other way around.
Possible outcomes of Lotka-Volterra
- two species may coexist stably
- species 1 may always win (N1 = K1, N2 = 0)
- species 2 may always win (N2 = K2, N1 = 0)
- identity of winner depends on starting Ns or whoever gets first advantage
What is equilibrium by the Lotka-Volterra model?
when N’s (number of individuals in a population) is no longer changing
- dN/dt = 0
- constant species composition
What do the outcomes of Lotka-Volterra depend on?
Values of K and alphas.
Co-existence requires…
both species to inhibit their own growth more than they inhibit each other
Stability
The ability of a system to return to equilibrium following a disturbance (fire, flood)
Coexistence (by the LV model)
occurs when two or more species have non-zero population sizes at equilibrium (niches cannot overlap too much or they will outcompete each other)
Principles of Competitive exclusion
- L-V predicts that for two species to coexist, competition must be weaker between species than among members of the same species
(this is not really what occurs in real life)
MacArthur’s warblers
Coexist by niche partitioning
- warblers seemed to have the same niche but really they were feeding on different parts of the tree
Gause (1934)
“As a result of competition two similar species scarcely ever occupy similar niches’
- studied competition between protozoa (some species could coexist and others couldn’t)
coexisting similar species….
evolve differences
Character displacement
describes evolutionary change that occurs when two similar species inhabit the same environment (similar species living in sympatry will diverge in some character traits but the same species living in separate areas will not have the same character displacement)
Paradox of the plankton
Written about by Hutchinson
- Why are there so many species of phytoplankton in the ocean when they all require the same resources (light, CO2, N, P, and micronutrients)
(similar to paradox of the rainforest)
Why is the principle of competitive exclusion not generally applicable to real life scenarios?
Competitive exclusion is less likely to go to completion
- Other factors like resources, weather, biotic and abiotic factors are more likely to keep a population below carrying capacity
- biological effects interact with physical effects: different outcomes in different environments
Community composition
which species
species richness
how many species
Connell barnacle experiments
- zone upper limits set by desiccation
- lower limits set by competition for space on the rock
- competition is asymmetrical: remove Balanus and Chthamalus extends downwards, but if you remove Chthamalus balanus does not extend upwards (what is limiting range)
What solved the Paradox of the plankton?
- LV models are way too simple
- most communities are not at competitive equilibrium
- real populations are kept below carrying capacity by weather, disease, predators
- real conditions fluctuate favouring different species at different times
Competition is generally expected to….
decrease species diversity (is a superior competitor excludes other species)
Why are lab experiments of competition generally poor indicators of real life?
Simple lab experiments are species-poor and real ecosystems are species rich and much more complex (hard to pin down actual factors of causation)
