4. Competition

Question 1

what are species interactions? 7

Answer 1

1. complex interactions occur that determine abundance and distribution of species 2. competition - 2 species use same limited resource to the detriment of each other 3. predation - one animal eats another 4. herbivory - one animal eats a plant 5. parasitism - symbiotic relationship detrimental to one party and beneficial to the other - macropathogens 6. disease - association between micropathogenic organism and host to detriment of host 7. mutualism - symbiotic relationship that benefits both partners

Question 2

What is exploitative/scramble competition? 3

Answer 2

1. organisms use common resource in short supply 2. indirectly prevents growth of each other 3. detriment appears because resource is no longer available

Question 3

What is interference/contest competition? 3

Answer 3

1. organisms directly harm each other, even if resource is abundant 2. can be by aggression or dangerous chemicals 3. aggression can cause additional negative effects, esp, in carnivores

Question 4

What is intraspecific competition? 2

Answer 4

1. Usually more intense than interspecific competition 2. genomes more similar so want some resources in sam eway

Question 5

What is the Lotka-Volterra Growth Model? 6

Answer 5

1. 2 sets of equations, one for predator-prey interactions and one for competition
2. based on logistic growth curve
3. growth density dependant on the carrying capactiy
4. shows one species

Question 6

How do you calculate population growth rate?

Answer 6

Question 7

How do you calculate competition using the lotka-volterra growth model?

Answer 7

Question 8

How do you determine outcomes with Lotka-Volterra diagrams? 6

Answer 8

1. the hyponteneuse is the carrying capacity
2. this is called the zero isocline
3. beneath the line, the population can increase
4. above the line it decreases
5. on the line, there is no change

Question 9

What is competitive exclusion on a stable equilibrium? 6

Answer 9

1. below both lines, both species can increase
2. between lines, only outer species can increase
3. above both lines, neither can increase
4. outer line eventually dominates
5. species with hightest k wins

Question 10

What is competitive exclusion on an unstable equilibrium? 4

Answer 10

1. Species can coexist at point where lines cross
2. suggestive of self regulating populations rather than regulation by another species
3. if system favours one species over the other, competitive exclusion occurs.

Question 11

What is coexistence with a stable equilibrium? 4

Answer 11

1. coexistence if intraspecific competition is stronger than interspecific competition
2. both species are self redulating before impact by other species begins
3. relationship between inter and intraspecific competition determines outcomes

Question 12

What are the limitations of lokta-volterra diagrams? 2

Answer 12

1. describes competition without mechanisms
2. does not tell us if coexistence and exclusion actually happen in nature

Question 13

Describe Birch’s beetle experiment of 1953. 4

Answer 13

1. 2 beetle species - Rhizopertha and Calanra - grown in lab together
2. Populations monitored
3. in competition for wheat
4. rhizopertha population declines and calandra dominates - competitive exclusion

Question 14

Descrobe Gause’s yeast and microbe experiements of the 1930s. 3

Answer 14

1. grew 2 microbe species together in one test tube - coexistance
2. grew yeast in pure and mixed populations
3. overall, volume less in mixed populations but coexistence possible in reasonable quantities

Question 15

What were the limitations of Birch and Gause’s experiements? 2

Answer 15

1. in 1945, Crombie found that coexistence of 2 similar beetles to Birch’s had different larval feeding habits but same adult feeding habits
2. In 1934, Gause found that coexisting yeast fed at different levels in the substrate of tube

Question 16

What is Gause’s hypothesis? 5

Answer 16

1. Complete competitors cannot coexist
2. many species appear to coexist in nature
3. hypothesized that competition is relatively rare in nature
4. meta-analysis suggests high mean effect of interspecific competition so it must occur
5. also hypothesised that competition is very common and so species have adapted to miimise effects

Question 17

What are funamental and realised niches? 2

Answer 17

1. Fundamental niche - a multidimensional space of resources needed by an organism in the absence of competition
2. the realised niche is the area of fundamental niche that is actually realised

Question 18

What is the effect of competition in niche space? 2

Answer 18

1. Competition with other species can reduce niche breadth, while optimal remains the same
2. iif outcompeted at optimum, the species distribution shirts to peripheral parts of fundamental niche

Question 19

Give an example of spatial niche partitioning of microbes in soil. 10

Answer 19

Question 20

Describe competion for N in the soil. 5

Answer 20

1. Animals and plants compete for n, but much is locked away in organic material
2. microbes are best competitors, take up ammonia and nitrates faster
3. organic N is more accessible to microbes
4. trees provide microbes with carbon, so trees gain nitrogen from microbes, as carbon stimulates them, microbes eventually die and trees get nitrogen
5. soil organic matter is inaccessible to plants

Question 21

What are the advantages of temporal and spatial niche paritions in soil? 4

Answer 21

1. microbes win in shot term, esp. in low nitrogen environment
2. net flux of nitrogen to plants in the long term
3. ecological importance - prevents n leaching
4. facilitates developments of mutualistic interactions

Question 22

Ecology. C. Krebs. 2014.

What is Tilman’s model? 2

Answer 22

1. allows understanding of resources and consumption in competitive interactions
2. essential components for understanding interactions

Question 23

Ecology. C. Krebs. 2014.

How does competition work in natural populations? 8

Answer 23

1. Competitive exclusion would not occur:
2. in unstable environments that don’t reach equilibrium and have colonizing species
3. non-competitive environments
4. Fluctuating environments where already below carrying capacity
5. coexistence of animals may be due to slight differences eg. feeding from different parts of same plant
6. doesn’t explain plants n- may not be in equilibrium at all
7. Facilitation - some plants help each other
8. Gause’s hypothesis should be rejected as the difference at even one gene locus allowed coexistence

Question 24

Fundamentals of ecology. Odum and Barrett. 2005.

Summarise competition and coexistence 2

Answer 24

1. animals higher up tree of life more likely to use direct competition - more able
2. coexistence more likely in nature where others can leave