Competition Flashcards
Define ubiquitous and is competition considered to be ubiquitous?
Competition is ubiquitous = often observed
- competition plays central role in evolutionary theory via fitness
What is one of the maxims of biology made famous by Dobzhansky?
“Nothing in biology makes sense except in the light of evolution”
What are the fundamentals behind evolution by natural selection?
- More individuals are born than reproduce
- Limited resources
- Genetic variation
= selection if most fit for environmental conditions due to natural selection
Instead of survival of the fittest, what does natural selection really mean?
death of most individuals before they reproduce
What are the 3 components which determine an individuals fitness?
GSR:
G = growth
S = survival to maturity
R = reproductive output
What are the drivers of GSR?
- Individual traits- affecting ability to obtain and use resources to avoid mortality
Define: resources
anything that is consumed by organisms and in turn reduced in availability
Define: resources
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
What does limiting resources result in?
Resources are subject to competition and certain individuals evolve selected traits in order to be better at obtaining the resources
Name and define the different types of resources
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
What are limiting resources for plants?
Light- competed for above ground
Water- competed for below ground
Soil nutrients- nitrogen, phosphorus, potassium- competed for below ground
What are autotrophs?
Generates their own carbohydrates to feed themselves
How does the species richness vary among animals and plants and why is this?
Animal diversity much higher- 5-10 million species
Plants depend on a smaller range of resources- 400,000 species
What is the main resource limitation for animals?
Nitrogen for proteins- animals also require common salt which plants expend energy trying to get rid of
what are heterotrophs?
depend on other organisms for their nutrition
What is the main form of competition and what is it?
Exploitative competition = driving down of resource levels which deprives other individuals of it- individuals do not have to meet
Describe an example of exploitative competition
Hummingbirds- need certain flowers for nectar:
- these specific flowers = limited resource
- As hummingbird density increases = net gain made by individuals falls = GSR falls
What is another type of competition and what is it?
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
Give an example of interference competition
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
What is the difference between interspecific and intraspecific competition?
Interspecific = occurs within species
Intraspecific = occurs among species
- Both affect fitness but their consequences for populations and communities are different
Compare weak and strong intraspecific competitors
Weak = fail to reach adulthood or reproduce successfully
Strong = show no sign of being affected by competition = proportional contribution to next gen increases
How does the density of populations impact intraspecific competition
Low density = competiton hardly impacts individuals but as density increases, selection becomes stronger and impacts of fitness apparent
Describe an experiment that demonstrates affect of density on fitness + what types of competition is this?
= 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
Define: overcompensation
= A peak in density where it is too high that mortality rises above the rate of increase in density- driven by competition
What is scramble competition?
resources divided evenly between population so competition is balanced- eventually getting to the point where they all die
What is contest competition?
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
How are birth rates affected by competition and why?
Birth rates drop with competition as organisms have fewer resources available to allocate to their offspring
How does population density affect birth rates?
Increased density = fewer offspring by animals + fewer seeds produced by plants
lowe density = no effect
How does density affect growth rates and give an example.
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
What happens if 2 species share the same resource (Interspecific competiton?
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
Describe an example of competitive exclusion.
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
Describe an example of how diatoms coexist.
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
What is a common feature of coexistance of competing species?
Trade off of a stronger ability to acquire one resource against another = intraspecific competition exceeds interspecific competition
If one species is doing well and another isnt and they share the same resource, does this mean they’re competing? + example
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
What is a apparent competition?
= type of indirect competition in which competing organisms have the same predator- usually occuring when a prey species population grows which attracts more predatiors
