Competition

Question 1

State some biological interactions

Answer 1

Competition, Predation, Mutualism, Commensalism and Amensalism

Question 2

what is a niche

Answer 2

Niche - The range of resources and conditions over which an organism can survive and reproduce. The methods it uses to acquire resources

“…….an n-dimensional hypervolume of resource axes”, where n equals the number of environmental factors important to the survival and reproduction of a species.
Hutchinson, 1957
N = number of factors essential for successful survival and reproduction of that species.

Question 3

Name some types of niches

Answer 3

• Fundamental niche - where the organism can physiologically survive
Realised niche - other factors narrow the niche down to where it actually survives and reproduces

Question 4

types of competition

Answer 4

A study was done in Millport by Conell in the 1960’s . He found that that C. montagui was outcompeted by S. balanoidies on the lower shore, therefore, in Millport (the northern point in its range) the lower shore was in its fundamental niche but therefore not the realised niche.

* This is an example of interference competition, which involves direct, physical interactions. 
* Exploitative competition - indirectly compete, through a resource, quicker ect. (If one species of hermit crab found shell resources first that would be exploitative whereas if they then fought for it that would be interference. 
* Pre-emptive competition - luck.  (what larvae is around when bare rock opens up).

Question 5

sum up competitive exclusion principle

Answer 5

• Species occupying the same niche cannot co-exist
  
  • The greater the niche overlap, the greater the likelihood of competitive exclusion, leading to local extinction of one species
  • Leads to resource partitioning where they will try to lessen the competitor intensity where they will try to utilise different parts of the resource or perhaps access the resource at different times
  • Therefore, eventually, one species, a competitive dominant will prevail
  • Species co-existence is dependent on external forces restricting the dominant competitor.
  • Competitive hierarchies often result in organisms being separated out in space (share different parts of a resource)
  • Asymmetrical competition, when two species are competing one will fare worse of, and in some cases one species may actually fair better when it has a competitive subordinate.
  • A gradient or patchy distribution may occur between two species occupying different parts of a niche.

Question 6

Sigmoid Growth Curve

Answer 6

1. N = represents the number of individuals in our population
   
   2. Nt = N at a point t in time. T breeding seasons after we started our study.
   3. 5 ♂ and 5 ♀ snails = 10 = N at Year 0
   4. Assume each produces 10 young, and they breed only once in a season and then die
   5. Therefore, in year 1 there will be 50 individuals. Nt+1 = Ntx5
   6. Nt+1 = Nt x R R = reproductive rate
   • This describes a population that is breeding in separate discrete seasons, and would make a stepped growth curve.
   • dN/dt is the mathematical convention to summarise rate of change of the population of size N. It is equal to the number of individuals at the start multiplied by how fast they can reproduce.
   • K would cap the graph as it is the carrying capacity of our population.
   • R is the population growth rate

R = rNt ( 1 - Nt / K)

R = population growth rate R = dN/dt
r = intrinsic rate of increase of population
Nt = number of animals at time t
K = Carrying capacity
As N approaches K, this approaches 1, and ultimately R tends towards 0. Therefore the growth rate tends towards 0 as the population reaches its carrying capacity.

Question 7

Lotka-Volterra Equations of Competition

Answer 7

• This all builds to a famous set of equations called Lotka-Volterra Equations of Competition which are the basis of which ecologists can theoretically and mathematically describe competition, and use to test hypothesis about competition.

• Population growth curve of species 1:
dN1/dt  = r1N1 (1-N1/K1) measure of the proportion of resources currently being used

• Population growth curve of species 2:
dN2/dt  = r2N2 (1-N2/K2)

• α is competition co-efficient which builds in the effect of competition
If α = 3, then for every individual of species 2 present, the carrying capacity of species 1 is decreased by 3 individuals

* Population growth curve of species 1: dN1/dt  = r1N1 (1-N1/K1  -  α N2/K1)  The competition of species 2 on species 1, this is built from how strong competeively they are and how many individuals of species 2 are present. This shows how much of the resource is being used up by species 2. 
* Population growth curve of species 2: dN2/dt  = r2N2 (1-N2/K2 -  N1/K2). The opposite effect can be built in to the logistic equation of species 2, the similar effect backwards. 
* These equations can be used to manipulate different parameters.

Question 8

WIDER READING: give an example of interference competition on a rocky shore

Answer 8

Menge 1976-An example of Interference competition on a rocky shore
Organization of the New England Rocky Intertidal Community: Role of Predation, Competition, and Environmental Heterogeneity
• Mid-intertidal of exposed areas structured primarily by interspecific competition
• Space cleared firstly colonised byB.balanoides,M.edulissettle late summer and outcompete barnacles by August.
• Disturbance from fucoid whiplash inhibitsB.balanoidessettlementinitially
Rate of competition slowed by vertical substrata

Question 9

WIDER READING: give an example of exploitative competition.

Answer 9

Underwood 1978-an example of exploitative competition over a resource
An Experimental Evaluation of Competition between Three Species of Intertidal Prosobranch Gastropods
• Three species,Neritaatramentosa,Bembiciumnanum(both gastropods)and the limpetCellanatramoserica
• All 3 showed increased mortality and reduced weight at increased densityover100 and 200 dayperiods
• Competing over microalgal food source
• Neritawas competitively superior to the other two species.Cellana, at high densities, adversely affectedBembicium.Neritawas not affected by high densities of either of the other two species
• Different feeding mechanisms offer explanation as to why there is variation between species
• AlthoughCellinacompetitively inferior toNeritathey still co-exist. Can be explained by distribution patterns and high recruitment rates ofCellina

Question 10

WIDER READING: give an example of resource partitioning (dolphin)

Answer 10

Oviedo 2007- An example of resource partitioning
Dolphin sympatric ecology in a tropical fjord: Habitat partitioning by bathymetry and topography as a strategy to coexist
• Golfo Dulce is a tropical ford in the southern pacific waters of Costa Rica
• TursiopstruncatusandStenellaattenuata
• 2 species of dolphin occupying different parts within the ocean, sympatric ecology in a tropical fjord.
• Habitat partitioning allowing co-existence
• Avoid competition tocounter its suppressor effects- although
• S.attenuatashowed greater numbers at deeper waters thanT.truncatus.

Question 11

WIDER READING: give an example of resource partitioning (copepods)

Answer 11

Laakman2009-An example of resource partitioning
Ecological niches of Arctic deep-sea copepods: Vertical partitioning, dietary preferences and different trophic levels minimize inter-specific competition
• two dominant calanoid copepod familiesEuchaetidaeandAetideidaein Fram Strait, Arctic Ocean
• Closely related species were usually restricted to different depth layers, resulting in a multi-layered vertical distribution pattern.
• Vertical partitioning was an important mechanism to avoid inter-specific competition.
• They differed in fatty acid composition and trophic level, indicating different food preferences.