Competition

Question 1

Define ubiquitous and is competition considered to be ubiquitous?

Answer 1

Competition is ubiquitous = often observed
- competition plays central role in evolutionary theory via fitness

Question 2

What is one of the maxims of biology made famous by Dobzhansky?

Answer 2

“Nothing in biology makes sense except in the light of evolution”

Question 3

What are the fundamentals behind evolution by natural selection?

Answer 3

1. More individuals are born than reproduce
2. Limited resources
3. Genetic variation

= selection if most fit for environmental conditions due to natural selection

Question 4

Instead of survival of the fittest, what does natural selection really mean?

Answer 4

death of most individuals before they reproduce

Question 5

What are the 3 components which determine an individuals fitness?

Answer 5

GSR:
G = growth
S = survival to maturity
R = reproductive output

Question 6

What are the drivers of GSR?

Answer 6

• Individual traits- affecting ability to obtain and use resources to avoid mortality

Question 7

Define: resources

Answer 7

anything that is consumed by organisms and in turn reduced in availability

Question 8

Define: resources

Answer 8

anything that is consumed by organisms and in turn reduced in availability

• can be raw materials required for GSR as well as limiting factors e.g. solar energy, space

Question 9

What does limiting resources result in?

Answer 9

Resources are subject to competition and certain individuals evolve selected traits in order to be better at obtaining the resources

Question 10

Name and define the different types of resources

Answer 10

External sources = supply rate is unaffected by competition
Internal sources = supply influenced by competition
Renewable = continously regenerated so unaffected by competition e.g. sunlight
Non-renewable = availability affected by competition and usually derived from internal sources of the ecosystem e.g. space

Question 11

What are limiting resources for plants?

Answer 11

Light- competed for above ground
Water- competed for below ground
Soil nutrients- nitrogen, phosphorus, potassium- competed for below ground

Question 12

What are autotrophs?

Answer 12

Generates their own carbohydrates to feed themselves

Question 13

How does the species richness vary among animals and plants and why is this?

Answer 13

Animal diversity much higher- 5-10 million species
Plants depend on a smaller range of resources- 400,000 species

Question 14

What is the main resource limitation for animals?

Answer 14

Nitrogen for proteins- animals also require common salt which plants expend energy trying to get rid of

Question 15

what are heterotrophs?

Answer 15

depend on other organisms for their nutrition

Question 16

What is the main form of competition and what is it?

Answer 16

Exploitative competition = driving down of resource levels which deprives other individuals of it- individuals do not have to meet

Question 17

Describe an example of exploitative competition

Answer 17

Hummingbirds- need certain flowers for nectar:
- these specific flowers = limited resource
- As hummingbird density increases = net gain made by individuals falls = GSR falls

Question 18

What is another type of competition and what is it?

Answer 18

Interference competition = type of direct competition where an organism actively interferes with anothers ability to obtain a resource- can occur among individuals of the same species or differing species

Question 19

Give an example of interference competition

Answer 19

New Mexico desert ants- 2 species coexist and feed on same seeds + insect prey:
- long-legged ants get up early and block nests of red harvester ants
- These blockages take a while to clear so long-legged ants only have access to the resources

Question 20

What is the difference between interspecific and intraspecific competition?

Answer 20

Interspecific = occurs within species
Intraspecific = occurs among species

• Both affect fitness but their consequences for populations and communities are different

Question 21

Compare weak and strong intraspecific competitors

Answer 21

Weak = fail to reach adulthood or reproduce successfully

Strong = show no sign of being affected by competition = proportional contribution to next gen increases

Question 22

How does the density of populations impact intraspecific competition

Answer 22

Low density = competiton hardly impacts individuals but as density increases, selection becomes stronger and impacts of fitness apparent

Question 23

Describe an experiment that demonstrates affect of density on fitness + what types of competition is this?

Answer 23

= Scramble competiton- Flour beetles:

Population density can be manipulated by changing egg number, but total resource (food) remains constant

RESULTS:
- When resources are abundant = death rates unaffected by density
- not too many eggs = mortality not dependent on density
- Density increases = death rates rise overtaking increase in density and survival peaks
- Too many eggs = all larvae will die

Question 24

Define: overcompensation

Answer 24

= A peak in density where it is too high that mortality rises above the rate of increase in density- driven by competition

Question 25

What is scramble competition?

Answer 25

resources divided evenly between population so competition is balanced- eventually getting to the point where they all die

Question 26

What is contest competition?

Answer 26

Involves a fixed number of winners that survive and rest die:

• rate of mortality increases at same rate as density above a certain level then remains constant

Question 27

How are birth rates affected by competition and why?

Answer 27

Birth rates drop with competition as organisms have fewer resources available to allocate to their offspring

Question 28

How does population density affect birth rates?

Answer 28

Increased density = fewer offspring by animals + fewer seeds produced by plants
lowe density = no effect

Question 29

How does density affect growth rates and give an example.

Answer 29

Growth rates decline with density:

e.g. Juvenile reindeer use summer months to grow to increase chance of survival in winter and successful reproduction in future
- as their population density increases = body size decreases

Question 30

What happens if 2 species share the same resource (Interspecific competiton?

Answer 30

Stronger competitor will exclude other species and prevent them from coexisiting

= no 2 species can occupy the same niche- stronger competitor will always exclude weaker competitor

Question 31

Describe an example of competitive exclusion.

Answer 31

e.g. Diatoms = planktonic organisms that form shells- 2 types that can maintain themselves in silicate solution:
1. Asterionella
2. Synedra = reduces silicate levels further than asterionella and can therefore drive it extinct
- can even occuer if 10 x more asterionella

Question 32

Describe an example of how diatoms coexist.

Answer 32

Cyclotella = competes more strongly for silicate
Asterionella = competes more strongly for phosphate

When combined- if one particular resource is in short-supply then stronger competitor wins
but if both resources are balanced then both diatoms can coexist + each species limit their own populations more than the other

Question 33

What is a common feature of coexistance of competing species?

Answer 33

Trade off of a stronger ability to acquire one resource against another = intraspecific competition exceeds interspecific competition

Question 34

If one species is doing well and another isnt and they share the same resource, does this mean they’re competing? + example

Answer 34

No known as apprent competition = e.g. Reindeer and moose:
reindeer = found in forested areas
if forested area is logged then reindeer decline and moose populations rise
Moose are not outcompeting reindeer instead the logged habitat is unfavourable to them = decreasing their population and moose benefit increasing their population
- increase in moose population increases predator population of wolves which mediates their population as well as preying on reindeer

Question 35

What is a apparent competition?

Answer 35

= type of indirect competition in which competing organisms have the same predator- usually occuring when a prey species population grows which attracts more predatiors