Lecture 19: Community Ecology

Question 1

intraspecific competition

Answer 1

competition within a species between members of said species (among conspecifics) ex. population running out of food because there are too many individuals

Question 2

interspecific competition

Answer 2

competition between species (among heterospecifics)

Question 3

Lotka-Volterra Equations

Answer 3

models two species competing (outgrowth of the logistic equation)

Question 4

competition

Answer 4

negative effects for both species

Question 5

predation

Answer 5

benefits predator, hurts the prey

Question 6

mutualism

Answer 6

beneficial for both

Question 7

exploitative competition

Answer 7

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).

Question 8

Interference competition

Answer 8

also known as contest competition, it is a direct interaction between species, for example territory battles (ants fighting).

Question 9

Are invasive species superior competitors?

Answer 9

Yes, usually their impact on native species is greater than the other way around.

Question 10

Possible outcomes of Lotka-Volterra

Answer 10

• 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

Question 11

What is equilibrium by the Lotka-Volterra model?

Answer 11

when N’s (number of individuals in a population) is no longer changing

• dN/dt = 0
• constant species composition

Question 12

What do the outcomes of Lotka-Volterra depend on?

Answer 12

Values of K and alphas.

Question 13

Co-existence requires…

Answer 13

both species to inhibit their own growth more than they inhibit each other

Question 14

Stability

Answer 14

The ability of a system to return to equilibrium following a disturbance (fire, flood)

Question 15

Coexistence (by the LV model)

Answer 15

occurs when two or more species have non-zero population sizes at equilibrium (niches cannot overlap too much or they will outcompete each other)

Question 16

Principles of Competitive exclusion

Answer 16

• 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)

Question 17

MacArthur’s warblers

Answer 17

Coexist by niche partitioning

- warblers seemed to have the same niche but really they were feeding on different parts of the tree

Question 18

Gause (1934)

Answer 18

“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)

Question 19

coexisting similar species….

Answer 19

evolve differences

Question 20

Character displacement

Answer 20

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)

Question 21

Paradox of the plankton

Answer 21

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)

Question 22

Why is the principle of competitive exclusion not generally applicable to real life scenarios?

Answer 22

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

Question 23

Community composition

Answer 23

which species

Question 24

species richness

Answer 24

how many species

Question 25

Connell barnacle experiments

Answer 25

• 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)

Question 26

What solved the Paradox of the plankton?

Answer 26

• 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

Question 27

Competition is generally expected to….

Answer 27

decrease species diversity (is a superior competitor excludes other species)

Question 28

Why are lab experiments of competition generally poor indicators of real life?

Answer 28

Simple lab experiments are species-poor and real ecosystems are species rich and much more complex (hard to pin down actual factors of causation)