Positive and negative interactions

1. Positive and negative interactions Interspecific 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

2. 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.

3. 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. Pollination 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.

4. Intraspecific competition Canis lupus Mytilus edulis 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  Mate competition

5. Territoriality The variance in distanceis much less than the meandistance Territoriesimply a moreor less evendistribution of individuals in space Overlap Territoriality is a form of avoidance of intraspecificcompetition Territory Home range Territory Home range Home ranges might overlap

6. 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 l=aD2 and w=bD2 Trees is a forst have certain distances to each others Therefore The -3/2 self thinning rule Modified from Osawa and Allen (1993)

7. Density dependent regulation of population size results from intraspecific competition Density independence Density dependence Tribolium confusum Data from Bellows 1981. J. Anim. Ecol. 50 Density dependence Density independence Vulpia fasciculata Data from Ebert et al. 2000. Oecologia 122

8. Data from Allen 1972, R. Int. Whaling Comm. 22. Salmo trutta Density dependence Peak reproduction at intermediate densityy Density independence 1 Nt/Nt+1 First order order recursive function of density dependent population growth Nicholson and Baily model 1/r Nt K

9. Georgii Frantsevich Gause (1910-1986) Competitive exclusion principle In homogeneous stable environments competitive dominant species attain monodominancy. Paramecium caudatum Paramecium aurelia Joint occurrence Data from Gause 1943, The Struggle for Existence Applying this principle to bacterial growth Gause found a number of antibiotics

10. Interspecific competition Tribolium castaneum Tribolium confusum Data from Park 1954. Phys. Zool. 27. Two species of the rice beetle Tribolium grown together compete differently in dependence on microclimatic conditions.

11. 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

12. 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.

13. Competition for enemy free space (apparent competition) Ephestia kuehniella Plodia interpunctella Venturia canescens Extinction Data from Bonsall and Hassell 1997, Nature 388 Predator mediated competition might cause extinction of the weaker prey

14. Character displacement and competitive release Chalcosoma caucasus 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) Rhinoceros beetles Chalcosoma atlas 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. Raven Dietarywidth Bodey et al. 2009. Biol.Lett 5: 617 Raven + Crows Raven

15. Predation Erigoneatra Canada lynx and snowshoe hare Specialist predator Generalist predator Oligophages Polyphages Monophages

16. Trade-offs in foraging Maximum yield Animals shouldadopt a strategy to maximuzeyield Optimalforagingtheory Stopping point Preyquality Holling’soptimalforagingtheory Starvation Searchingtime Predictedenergyintake from travel and handlingtime Great titsforageatsite of differentquality How longshould a birdvisiteachsite to haveoptimalyield? 10 20 Predictedenergyintake from traveltime 18 15 3 11 4 Parus major 9 17 8 Cowie 1977

17. 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 Bracyonus calyciflorus Chlorella vulgaris Most important are regular climatic variations like El Nino, La Nina, NAO. Data from Yoshida et al. 2003, Nature 424

18. 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. • Any deviation from the assumption of the Lotka Volterra model tends to stabilize population: • Prey aggregration • Density dependent consumption • Functional responses The Lotka Volterra models predicts unstable delayed density dependent cycling of populations

19. Environmental heterogeneity and predator prey cycles Typhlodromus occidentalis Eotetranychus sexmaculatus Simple unstructured environment Heterogeneous environment Habitat heterogeneity provides prey refuges and stabilizes predator and prey populations

20. Functional response Type II Holling response Type III Holling response Type I response Microplitis croceipes Calliphora vomitoria Predator attak rates are not constant as in the Lotka Volterra model Microplitis croceipes Calliphora vomitoria

21. 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 Dynamic equilibrium 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.

22. Herbivory Plant defensesagainstherbivors 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. Alcaloide (aminoacidderivatives): nicotine, caffeine, morphine, colchicine, ergolines, strychnine, and quinine Terpenoide, Flavonoids, Tannins Mechanicaldefenses: thorns, trichomes… Mimicry Mutualism: Ant attendance, spiderattendance Digitalis

23. 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)