competetion and predation- roles and conflicts


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Species Interactions:

Species Interactions Competition – Interspecific & Intraspecific Predation – Carnivory, Herbivory & Parasitism Mutualism or Symbiosis Commensalism Ammensalism Proto-cooperation

Competition - Interspecific:

Competition - Interspecific The essence of interspecific competition is that individuals of one species suffer a reduction in fecundity, growth or survivorship as a result of resource exploitation or interference by individuals of another species. This competition is likely to affect the population dynamics of the competing species, and the dynamics, in their turn, can influence the species’ distributions and their evolution.

Interspecific Competition Models:

Interspecific Competition Models

Interspecific Competition Models:

Interspecific Competition Models Strong interspecific competitors outcompete weak interspecific competitors

Competition in fishes:

Competition in fishes

Competition in barnacles:

Competition in barnacles

Competition in microbes:

Competition in microbes

Competition in birds:

Competition in birds

Evolutionary Significance of Interspecific competition:

Evolutionary Significance of Interspecific competition When two species compete, individuals of one or both species may suffer reductions in fecundity and/or survivorship, as we have seen. The fittest individuals of each species may then be those that (relatively speaking) escape competition because they utilize the habitat in ways that differ most from those adopted by individuals of the other species. Natural selection will then favor such individuals, and eventually the population may consist entirely of them. The two species will evolve to become more different from one another than they were previously; they will compete less, and thus will be more likely to coexist.

Evolutionary Significance of Interspecific competition (contd.):

Evolutionary Significance of Interspecific competition (contd.) The ecological effects are, broadly, that species may be eliminated from a habitat by competition from individuals of other species; or, if competing species coexist, that individuals of at least one of them suffer reductions in survival and/or fecundity. The evolutionary effects appear to be that species differ more from one another than they would otherwise do, and hence compete less. The two major observable effects of competition and evolution are: Competitive release Character displacement

Competitive release:

Competitive release In northern Israel, two seed—eating gerbiline rodents exhibit exclusive distributions. Gerbillus allenbyi is the only species inhabiting coastal sand dunes between Tel Aviv and Mt. Carmel. Meriones tristrami is also found in the same coastal region, but there it is restricted to nonsandy habitats. However, in the coastal area north of Mt. Carmel where G. allenbyi does not occur, M. tristrami inhabits dunes. This type of distribution is usually interpreted to result from competition. A perturbation experiment conducted in the narrow transition strip between soil and sand in an area where the above species are sympatric revealed no ongoing competition between the two species. It is suggested that strong interspecific competition occurring in the past resulted in genetically determined habitat selection in the present.

Character displacement:

Character displacement Native geographic ranges (I–VII) of Herpestes javanicus ( j), H. edwardsii (e) and H. smithii (s)

Character displacement (contd.):

Character displacement (contd.)

Evolution-Competition experiments:

Evolution-Competition experiments

Evolution-Competition experiments:

Evolution-Competition experiments


Predation Predation, put simply, is consumption of one organism (the prey) by another organism (the predator), in which the prey is alive when the predator first attacks it. Types of predators: True predators Grazers Parasites

Predatory responses:

Predatory responses

Food preference:

Food preference


Switching switching involves a preference for food types that are common when might switching arise? increased probability of orientating toward a common prey type increased probability of pursuing a common prey type. increased probability of capturing a common prey type. increased efficiency in handling a common prey type. MAY HAVE EVOLUTIONARY CONSEQUENCES OVER TIME!!


Switching Guppies fed with mixed diet of tubificids and fruitflies Sticklebacks fed with Gammarus and Artemia

The dynamics of predation:

The dynamics of predation

Crowding and predation:

Crowding and predation The effects of intraspecific competition, and of a decline in predator consumption rate with predator density, can be investigated by modifying the Lotka–Volterra isoclines. At low prey densities there is no intraspecific competition, and the prey isocline is horizontal as in the Lotka–Volterra model. But as density increases, it is increasingly the case that prey densities below the isocline (prey increase) must be placed above the isocline (prey decrease) because of the effects of intraspecific competition.

Crowding and predation:

Crowding and predation (b) Mutual interference amongst wolves, Canis lupus, preying on moose, Alces alces . (c) The same data but with wolf kill rate plotted against the moose : wolf ratio. The fitted curve assumes a dependence of kill rate on this ratio, but also that the wolves may become ‘saturated’ at high moose densities (see Section 10.4.2). This curve fits better than any for which kill rate depends on either predator density (e.g.(b)) or prey density.

Crowding and predation:

Crowding and predation

Multiple equilibrium:

Multiple equilibrium sudden changes in abundance: multiple equilibrium – or sudden changes in the environment

Evolutionary significance of predation:

Evolutionary significance of predation The "rare-enemy principle." Predators that rarely attack a given prey species, either because they themselves are rare or because they prefer other prey, are unlikely to cause a measurable response in the predation-related traits of the prey. Similarly, prey species that constitute a sufficiently small proportion of the predator's diet will not have a significant effect on the predator's capture-related traits.

Evolutionary significance of predation:

Evolutionary significance of predation Marginal benefits (or costs) of change it is the rate of change of benefits with a change in the trait that is important in determining the evolutionary fate of the trait. the evolutionary equilibrium of a continuous trait occurs where the rate of change in fitness benefits with trait value is equal to the rate of change in fitness costs as with any other evolving trait, the rate of change of the trait increases as the additive genetic variance in trait value increases, and it decreases as the generation time increases. thus, when predators have a much longer generation time than prey, their main opportunity for increasing capture rate over evolutionary time is often by having a much greater genetic variance for traits that influence capture rate.

Evolution-predation experiments:

Evolution-predation experiments Garter snakes & Toxic newt decreased maximal speed of resistant snakes is compensated for by their ability to partially overcome the paralytic effects of the toxin after ingesting newts

Conflicts in competition and predation on evolution:

Conflicts in competition and predation on evolution Changes in snout-vent length and hind-limb length is more significant after competition treatment as compared to predator treatment

Conflicts in competition and predation on evolution:

Conflicts in competition and predation on evolution Differential responses of stamina and perching behavior after competition and predator treatments



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