Predator-prey relationships (that is, neither competitive nor mutualistic relationships) have been seen as providing the necessary stability for almost infinite numbers of species to exist in ecosystems. Such relationships do so by keeping the size of species populations in check at supportable levels.
Stefano Allesina and Si Tang, researchers at the University of Chicago, have studied such relationships. Their recent investigations have noted that, "When prey are high, predators increase and reduce the number of prey by predation. When predators are low, prey decrease and thus reduce the number of predators by starvation. These predator/prey relationships thereby promote stability in ecosystems and enable them to maintain large numbers of species.
By contrast, mutualistic relationships may reinforce the growth of large populations and competitive relationships may depress population numbers to the point of ecological instability."
The term carnivore is used in a variety of ways. The general ecological definition of a carnivore is an organism that feeds on animals, as opposed to feeding...
Predator-prey cyclesLast Updated on 2014-07-08 14:53:04Predator-prey cycles are characterized by regularly spaced increases and decreases in the population sizes or densities of a predator and its prey. Classically, the predator is a carnivorous species and the prey is an herbivorous species. However, carnivores that prey on other carnivores, herbivores feeding on plants, and even parasites attacking their host organisms are sometimes considered to have the same relationship, and so to be predator-prey systems. The predator population’s fluctuations follow those of the prey population through time. That is, the prey population begins to increase while the predator population is still decreasing and the prey population decreases while the predator population is still increasing. The classic (and simplest) explanation of these cycles is that the predator drives the changes in the prey population (by catching and killing its members) and... More »
Metapopulation dynamics of wild dogs in South AfricaLast Updated on 2014-07-02 13:56:37
Ideally, species should be protected in areas large enough to allow for natural demographic and genetic processes. However, in realty, species often occur in small and isolated patches of suitable habitat embedded in human-dominated landscapes. In metapopulation ecology, landscapes are viewed as networks of habitat patches (fragments) in which species occur as discrete local populations connected by migration. The dynamics of such a metapopulation is characterised by (asynchronous) local extinction and recolonisation events.
However, human modification of the landscape between habitat patches, the so-called matrix, often prevents migration. While establishing ‘corridors’ through the matrix may allow dispersing individuals to move from one habitat patch to another, this is often problematic in practice. This raises the question of how metapopulation viability can be... More »
HerbivoreLast Updated on 2014-06-29 19:25:53A herbivore is an animal that obtains its energy and nutrients by feeding on plants. Different types of herbivores eat different plant parts. For example, folivores feed on leaves, frugivores feed on fruits, granivores feed on seeds, pollinivores feed on pollen, and nectarivores feed on nectar. Herbivores can vary greatly in size, ranging from the largest terrestrial animals (elephants) and large marine mammals such as manatees and dugongs, to small insects, nematodes, and thrips. Herbivores are primary consumers (they receive their energy by consuming primary producers), so they play an important trophic role in ecological communities and food webs.
Because mature leaves are low in nutrients, and difficult to digest because of their high cellulose content, animals use many different strategies to eat leaves. Animals that feed on grass leaves are generally... More »
Altruistic behaviorsLast Updated on 2014-06-23 18:00:42
Altruistic traits are traits that reduce the fitness (survival or reproduction) of the individual with the trait (known as the “actor”) while increasing the fitness of other individuals (known as the “recipients”).
A classic example of an altruistic behavior is the “warning call” given by many species of animals including ground squirrels, prairie dogs, and passerine birds. If an individual observes an attacking predator it may give a call that has two effects. First, when other nearby individuals hear the call they recognize that danger is near and flee to safety. Individuals that hear the early warning (the recipients) benefit by having a decreased chance of being killed by the predator. However, by giving the warning call, the caller (the actor) delays his/her opportunity to flee to safety and attracts the attention of the predator, thus... More »
Top-down controlLast Updated on 2014-06-23 17:39:31
All organisms require energy and nutrients in some form to survive and grow. Thus, the existence and total biomass of ecosystems are ultimately regulated from the "bottom up", that is, by availability of resources such as sunlight, inorganic nutrients, water and other abiotic factors. Nevertheless, on more localized scales, the abundances of organisms at lower trophic levels can be strongly affected by their own predation, that is, by top-down control. Ecosystems often have been assumed to be controlled from the bottom-up, wherein nutrients and light stimulate primary production by plants, and the greater primary production in turn supports more animal production at higher trophic levels. But this is not the whole story. A simple way to envision top-down control is as follows: because the predator eats prey, the prey population is reduced, so when predators are removed,... More »
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