Positive and negative interactions. I nterspecific competition. Competition is an interaction between individuals of the same or of different species membership, in which the fitness of one is lowered by the presence of the other. Predation. Herbivory is a form of parasitism.
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Positive and negative interactions
Competition is an interaction between individuals of the same or of different species membership, in which the fitness of one is lowered by the presence of the other.
Herbivory is a form of parasitism
Symbiosis is any type of relationship where two individuals live together
Amensalism is a relationship between individuals where some individuals are inhibited and others are unaffected.
Parasitoidism is a relationship between two individuals in which one member benefits while the other is not allowed to reproduce or to develop further
Parasitism is any relationship between two individuals in which one member benefits while the other is harmed but not killed or not allowed to reproduce.
Commensalism is a relationship between two individuals where one benefits and the other is not significantly affected.
Mutualism is any relationship between two individuals of different species where both individuals benefit.
Mutualism is the way two organisms of different species exist in a relationship in which each individual benefits. Mutualism is the oposite to interspecific competition.
Client– service relationships
In plant succession early arriving plants pave the way for later arrviing by modifying soil condition.
Mutualism is often linked to co-evolutionary processes
Facilitation is a special form of commensalism and describes a temporal relationship between two or more species where one species benefits from the prior (and recent) presence of others.
Facilitation generally increases diversity.
Scramble (exploitation, diffuse) is a type of competition in which limited resources within an habitat result in decreased survival rates for all competitors.
Contest (interference) competition is a form of competition where there is a winner and a loser
The variance in distanceis much less than the meandistance
Territoriesimply a moreor less evendistribution of individuals in space
Territoriality is a form of avoidance of intraspecificcompetition
Home ranges might overlap
Density dependent regulation and diffuse competition
The stem self thinning rule
Leaf area L increases with plant density N
L=lNwhere L is the average leaf area per plant. This area and mean plant weight w increase with stem diameter by
Trees is a forst have certain distances to each others
The -3/2 self thinning rule
Modified from Osawa and Allen (1993)
Density dependent regulation of population size results from intraspecific competition
Data from Bellows 1981. J. Anim. Ecol. 50
Data from Ebert et al. 2000. Oecologia 122
Data from Allen 1972, R. Int. Whaling Comm. 22.
Peak reproduction at intermediate densityy
First order order recursive function of density dependent population growth
Nicholson and Baily model
Georgii Frantsevich Gause (1910-1986)
Competitive exclusion principle
In homogeneous stable environments competitive dominant species attain monodominancy.
Data from Gause 1943, The Struggle for Existence
Applying this principle to bacterial growth Gause found a number of antibiotics
Data from Park 1954. Phys. Zool. 27.
Two species of the rice beetle Tribolium grown together compete differently in dependence on microclimatic conditions.
The Lotka – Volterra model of interspecific competition
Alfred James Lotka (1880-1949)
Vito Volterra (1860-1940)
At equilibrium: dN/dt = 0
Certain conditions allow for coestistence
If carrying capacity differs one species vanishes
If competitive strength differs one species vanishes
The Lotka Volterra model predicts competitive exclusion
But the oberserved species richness is much higher than predicted by the model.
The model needs
stable reproductive rates
stable carrying capacities
stable competition coefficients
Grassland are highly diverse of potentially competing plants
It needs also homogeneous environments
Randomy fluctuating values of r, K, a, and b.
a > b
K1 > K2
Unpredictability and changing environmental conditions as well as habitat heterogeneity and aggregation of individuals promote coexistence of many species.
Competition for enemy free space (apparent competition)
Data from Bonsall and Hassell 1997, Nature 388
Predator mediated competition might cause extinction of the weaker prey
Character displacement and competitive release
Interspecific competition might cause species to differ more in phenotype at where where they co-occur than at sites where they do not co-occur (characterdisplacement)
Interspecific competition might cause a lower phenotypic orecologicalvariability of two species at sites where both species compete.
Competitivereleaseis the expansion of speciesniches in the absence of interspecificcompetitors.
Bodey et al. 2009. Biol.Lett 5: 617
Raven + Crows
Canada lynx and snowshoe hare
Trade-offs in foraging
Animals shouldadopt a strategy to maximuzeyield
Predictedenergyintake from travel and handlingtime
Great titsforageatsite of differentquality
How longshould a birdvisiteachsite to haveoptimalyield?
Predictedenergyintake from traveltime
Specialist predators and the respective prey often show cyclic population variability
12 year cycle
Cycles of the predator follow that of the prey
Cycles might be triggered by the internal dynamics of the predator – prey interactions or by external clocks that is environmental factors of regular appeareance
Canada lynx and snowshoe hare
Hudson’s Bay Company
Data from MacLulick 1937, Univ. Toronto Studies, Biol. Series 43
Most important are regular climatic variations like El Nino, La Nina, NAO.
Data from Yoshida et al. 2003, Nature 424
The Lotka Volterra approach to specialist predators
e: mortality rate of the predator
r: reproductive rate of the prey
faN: reproductive rate of the predator
f: predator efficieny
aP: mortality rate of the prey
a: attack rate
The equilibrium abundances of prey and predator
In nature most predator prey relationships are more or less stable.
The Lotka Volterra models predicts unstable delayed density dependent cycling of populations
Environmental heterogeneity and predator prey cycles
Simple unstructured environment
Habitat heterogeneity provides prey refuges and stabilizes predator and prey populations
Type II Holling response
Type III Holling response
Type I response
Predator attak rates are not constant as in the Lotka Volterra model
Variability, chaos and predator prey fluctuations
Lotka Volterra cycles with fixed parameters a, e, f, r.
Lotka Volterra cycles with randomly fluctuating parameters a, e, f, r.
Stochasticity tends to stabilize populations
Any factor that provides not too extreme variability into parameters of the predator prey interaction tends to stabilize populations.
Fixed parameter values cause fast extinction.
Many plants produce secondary metabolites, known as allelochemicals, that influence the behavior, growth, or survival of herbivores. These chemical defenses can act as repellents or toxins to herbivores, or reduce plant digestibility.
nicotine, caffeine, morphine, colchicine, ergolines, strychnine, and quinine
Terpenoide, Flavonoids, Tannins
Mechanicaldefenses: thorns, trichomes…
Mutualism: Ant attendance, spiderattendance
Functions of herbivores in coral reefs
Negative feedback loops occur when grazing is too low
Positive feedback loops occur when grazing is high
Herbivorous fish (Diadema)
Reduced structural complexity
Decreasing fish recruitment
Increased structural complexity
Increasing fish recruitment
Low coral cover
Low grazing intensity
High coral cover
High grazing intensity
Overfishing of herbivorous fish might cause a shift to algal dominated low divesity communities
Decreasing coral recruitment
Increasing algal cover
Increasing coral recruitment
Decreasing algal cover
Hay and Rasher (2010)