Interspecific interactions

Question 1

What is competition?

Answer 1

Two or more species using the same limited resource to the detriment of both. It is a reciprocally negative interaction.

Question 2

What are the different types of competition?

Answer 2

Exploitation: Organisms indirectly compete with other organisms for resources by exploiting resources to limit the availability to other organisms. e.g. a bear eating a fish prevents another from eating that fish.
Interference: Organisms directly vie for resources. i.e. male deer competing over a mate. - contest, chemical, overgrowth.

Question 3

why does competition occur?

Answer 3

When organisms share a common resource. When there is niche overlap there is competition.

Question 4

What does the Lotka-Volterra equation for competition entail?

Answer 4

Two logistic regressions. The number of individuals in species 2 impacts the growth rate of species 1 and vice versa.

Question 5

What are the three outcomes of competition?

Answer 5

1) both species coexist
2) species 1 becomes extinct
3) species 2 becomes extinct.

Question 6

What are examples of early competition experiments?

Answer 6

Classic studies of resource competition by Gause with Paramecium aurelia, Paramecium caudatum and Paramecium bursaria. Each grows well in isolation. When grown together, there is competitive exclusion of P.caudatum. In contrast P. bursaria and P. caudatum can coexist.

Question 7

What is Gause’s principle?

Answer 7

When the niches of two species overlap, there will be competition. If the overlap is extreme there will be competitive exclusion. As a result of competition two similar species scarcely ever occupy similar niches, but displace each other in a manner that each takes possession of certain kinds of food in which it has an advantage over its competitor.

Question 8

What is a fundamental niche?

Answer 8

The N-dimensional space where species can survive and reproduce indefinitely. includes environmental and behavioural conditions

Question 9

What is the realised niche?

Answer 9

Reflects the limited range of conditions a species actually occupies after competition.

Question 10

What is an example of competition and ecosystem flux?

Answer 10

PHYTOPLANKTON. They coexist in a similar lifestyle and the same pool of nutrients. There is constant competition. However, they coexist due to instability where the environment changes preventing extinction and constantly changing the rules.

Question 11

What is character displacement?

Answer 11

species are under selection to evolve niche dimensions with lower overlap. character displacement in nature is rare. It leads to evolution of physical characteristics among competitors that reflects their more specialised role in the ecosystem. e.g. Galapagos finches and Hawaiian honey creepers.

Question 12

What is indirect competition?

Answer 12

Competition is mediated through long lasting effects where competitors occupy different niches at different times/locations.

Question 13

Explain the evolution of competition

Answer 13

If two species compete for a resource the one that evolves an advantage will out compete the other. there is therefore strong selection on competitive advantage. Also some species evolve to avoid competition. If the food web is complex and avoidance is not possible, competitive ability will evolve.

Question 14

What is diffuse competition?

Answer 14

Niche overlap of an invader with most native species in a community,

Question 15

What is indirect competition?

Answer 15

Via a shared enemy, via another species.

Question 16

How are competition and predation linked?

Answer 16

Competition may cause populations to change in terms of predation and predation causes various effects in organisms that can alter competition.

Question 17

Example of link between competition and predation?

Answer 17

SPRINGBOKS: vigilance decreases with group size, individual on the edge of the herd are more vigilant than in the centre but compete with other herbivores for grass resources. Predation pressure influences local movements, Reduced predation = less movement = increased competition.

Question 18

What are the non-lethal effects of predation risk?

Answer 18

Prey are not unresponsive to predation. They have the ability to perceive the predation risk through public information, private information and management by predators. They pay costs for their response.

Question 19

Example of the effects of predation risk?

Answer 19

GREAT TITS: In the winterfat reserves are important to survive. Fat birds however make better targets and are less able to escape predation. body mass should be optimised in terms of the trade-off between starvation risk and predation. or YELLOWSTONE.

Question 20

What is public information?

Answer 20

Knowledge available to all i.e. abundance of predators at a site.

Question 21

What is private information?

Answer 21

Known to the individual only i.e. their own nesting history..

Question 22

How do predators manage prey?

Answer 22

Prey are more susceptible if they think that predation risk is low. This is most important for territorial animals. Repeated attacks in one area can build up information for the prey i.e. chemical cues, visual cues. The predator should minimise public information.

• target stragglers in group
• eating whilst hidden,
• being unpredictable. Accipiters (HAWK) are maximally random predators and their return to an area cannot be predicted.

Question 23

What are the effects of predation risk?

Answer 23

-abundance
-behaviour
-distribution
Information about predation is gained through sensory mode, it is then processed and level of risk judges. The animal combines costs and risks.

Question 24

What do logistic growth models need to account for?

Answer 24

INTRASPECIFIC INTERACTIONS:
-intra and intergeneration, intra and intersex, intraindividual.
-time lags
-allee effects
-sex ratios 
INTERSPECIFIC INTERACTIONS:
-Direct or indirect predator-prey
-stable point or stable limit cycles
-predation driving speciation
- non-lethal interactions through competition e.g. exclusion, niche partitioning or character displacement.