Introduction:

Population control is practice of artificially altering size of any animal population besides humans. It typically refers to act of restricting the size of animal population so that it remains manageable, as opposed to act of protecting species from excessive rates of extinction, that is is referred to as conservation biology.

Factors influencing population control:

Population control in animals can be influenced by the variety of factors. Humans can really influence size of animal populations they directly interact with. Different humans activities (like industrialization, hunting, farming, fishing, and urbanization) all impact different animal populations.

Animal population control is practice of intentionally altering size of any animal population besides humans. It may engage culling, translocation, or manipulation of reproductive capability. Growth of animal population may be restricted by environmental factors like food supply or predation.

Main biotic factors which effect population growth include:

- Food- both the quantity and quality of food are significant. Snails, for instance, can't reproduce successfully in the environment low in calcium, no matter how much food there is, as they need this mineral for shell growth.

- Predators as prey population becomes larger, it becomes easier for predators to find prey. If number of predators suddenly falls, prey species might increase in number very quickly.

- Competitors- other organisms may need same resources from environment, and so decrease growth of a population. For instance all plants compete for light.

- Parasites- These may cause disease, and slow down growth and reproductive rate of organisms within population.

Significant Abiotic factors affecting population growth comprise:

- Temperature- Higher temperatures speed up enzyme-catalyzed reactions and increase growth.

- Oxygen availability- affects rate of energy production by respiration.

- Light availability- for photosynthesis. Light may also control breeding cycles in animals and plants.

- Toxins and pollutants- tissue growth can be decreased by presence of, for instance, sulphur dioxide, and reproductive success may be influenced by pollutants like estrogen like substances.

Methods for active population control:

Animal euthanasia is frequently utilized as final resort to controlling animal populations. In Tangipahoa Parish, Louisiana, parish performed mass euthanasia on complete animal shelter population, comprising 54 cats and 118 dogs which were put to death because of widespread disease outbreak which spread among animals.

Neutering is another option available to control animal populations. Annual Spay Day USA event was established by Doris Day Animal League to promote neutering of pets, particularly those in animal shelters, so that population remains controllable.

Dynamics of Predation:

Populations of organisms don't remain constant; number of individuals within population changes, at times dramatically, from one time period to next. Ecologists have documented examples of such fluctuations in wide variety of organisms, comprising birds, algae, fish, invertebrates, frogs, and mammals like rodents, large herbivores, and carnivores. Ecologists have long wondered about factors which regulate such fluctuations, and early research recommended that resource availability plays significant role. Researchers found that when resources (food, nesting sites, or refuges) were restricted, populations would decline as individuals competed for access to limiting resources. Such bottom-up control helped to control population around carrying capacity.

Population cycles in the predator-prey system:

Modeling Predator-Prey Interactions:

Predator and prey populations cycle through time, as predators decrease numbers of prey. Lack of food resources in turn decrease predator abundance, and lack of predation pressure permits prey populations to rebound.

To survive and reproduce, individuals should get adequate food resources whereas simultaneously avoiding becoming food for the predator. Snowshoe share study shows role of both predator avoidance and food availability on population sizes.

Foraging Behavior:

In reality, predator-prey systems are complex; they frequently involve multiple predators and multiple kinds of prey. What factors affect kind of prey an individual predator takes? What influences foraging behavior of prey species? Under perfect situations, individual will encounter high-quality food items on regular basis. These preferred foods give the most nutritional advantage with fewest costs. Costs for organism may be handling time (like, time needed to catch prey or remove nut from its shell) or presence of chemicals, like tannins, which decrease nutritional quality of food item.

When preferred foods are scarce, organisms should switch to other, less-desirable alternatives. Point at which the organism must make this shift is not easy to forecast. It depends on several factors, comprising relative abundance of each of the foods, potential costs related with each food, and other factors, like risk of exposure to predators while eating. Field voles (Microtus agrestis) and bank voles (Clethrionomys glareolus) preferentially consume forbs and grasses, but they will turn to bark from trees when their preferred foods become scarce. Bark has poorer quality nutrients than do grasses and forbs. Additionally, voles should venture in open to approach trees to feed on bark, making them more vulnerable to predation by foxes that depend on sight to find their prey. Only when preferred foods are very difficult to find-as takes palce during times of population peaks-do voles switch to bark.

Increasing Complexity: Host-parasite Interactions

Francisella tularensis bacteria which cause tularemia are usually found in both voles and hares in Swedish boreal forest. Voles serve as host species for F. tularensis and don't display symptoms of disease; though other species, like mountain hares (Lepus timidus), do show symptoms of tularemia when infected. Infection by these bacteria may play role in population cycles of these species.

Parasites with complex life cycles need two hosts; in some of these systems, prey function as intermediate hosts for parasite, with predators acting as primary hosts. Parasites can influence behavior of intermediate host to make transmission to primary host more likely. These changes normally take place when parasite is at stage of its life cycle when it can effectively infect primary host. Behavioral changes which favor parasite transmission frequently involve unusual foraging behavior on part of intermediate host: foraging in locations which make individual more vulnerable to predation by primary host. Consequently, parasites can change size of prey populations during times of heavy infestation; as parasites infect primary host, predator populations may also decline.

Evolutionary Dynamics of Predator-Prey Systems: An Ecological Perspective

Evolution occurs in the evolutionary setting which normally involves interactions with other organisms. To explain such evolution, a structure is required that includes simultaneous evolution of interacting species. Procedure of coevolution which results from this is illustrated in predator-prey systems. With no more than qualitative information about evolutionary dynamics, few essential properties of predator-prey coevolution become evident. More thorough understanding needs specification of evolutionary dynamic; 2 models for this purpose are outlined, one from our own research on stochastic procedure of mutation and selection and other from quantitative genetics. Stability analysis of fixed points of evolutionary dynamical systems is analyzed and leads to conclusions about asymptotic states of evolution rather than different from those of game-theoretic methods. These differences become particularly significant when evolution comprises more than one species.

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