Allee effect - Wikipedia
Many species exhibit density-dependent reach high densities in some of their occupied habitats. Intraspecific competition is an interaction in population ecology, whereby members of the same . The negative density dependence in young wolf spiders is evident: as the population density increases further, .. Neutral theory · Occupancy–abundance relationship · Population viability analysis · Priority effect · Rapoport's. Population ecology is a sub-field of ecology that deals with the dynamics of species Population ecology is important in conservation biology, especially in the development of .. and exponential constants share the mathematical relationship below. variable is K (the carrying capacity of a population, density dependent).
As organisms are encountering each other during interference competition, they are able to evolve behavioural strategies and morphologies to out-compete rivals in their population.
For example, different populations of the northern slimy salamander Plethodon glutinosus have evolved varying levels of aggression depending on the intensity of intraspecific competition. In populations where the resources are scarcer, more aggressive behaviours are likely to evolve.
It is a more effective strategy to fight rivals within the species harder instead of searching for other options due to the lack of available food. In addition, a study on Chilean flamingos Phoenicopterus chilensis found that birds in a bond were much more aggressive than single birds.
The paired birds were significantly more likely to start an agonistic encounter in defense of their mate or young whereas single birds were typically non-breeding and less likely to fight. Mates are a fiercely contested resource in many species as the production of offspring is essential for an individual to propagate its genes.
Indirect[ edit ] Organisms can compete indirectly, either via exploitative or apparent competition. Exploitative competition involves individuals depleting a shared resource and both suffering a loss in fitness as a result. The organisms may not actually come into contact and only interact via the shared resource indirectly.
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For instance, exploitative competition has been shown experimentally between juvenile wolf spiders Schizocosa ocreata. Both increasing the density of young spiders and reducing the available food supply lowered the growth of individual spiders. Food is clearly a limiting resource for the wolf spiders but there was no direct competition between juveniles for food, just a reduction in fitness due to the increased population density.
This is also seen in Viviparous lizardor Lacerta vivipara, where the existence of color morphs within a population depends on the density and intraspecific competition. In stationary organisms, such as plants, exploitative competition plays a much larger role than interference competition because individuals are rooted to a specific area and utilise resources in their immediate surroundings.
Saplings will compete for light, most of which will be blocked and utilised by taller trees. Seeds that germinate in close proximity to the parents are very likely to be out-competed and die. Apparent competition occurs in populations that are predated upon. An increase in population of the prey species will bring more predators to the area, which increases the risk of an individual being eaten and hence lowers its survivorship.
- Occupancy–abundance relationship
- Density dependence
- Allee effect
Apparent competition is generally associated with inter rather than intraspecific competition, whereby two different species share a common predator.
An adaptation that makes one species less likely to be eaten results in a reduction in fitness for the other prey species because the predator species hunts more intensely as food has become more difficult to obtain. For example, native skinks Oligosoma in New Zealand suffered a large decline in population after the introduction of rabbits Oryctolagus cuniculus.
Contest[ edit ] Contest competition takes place when a resource is associated with a territory or hierarchical structure within the population.What is Co-Dependency - Mental Health with Kati Morton
In the case of Ctenophorus pictus lizards, males compete for territory. Density-dependent habitat selection[ edit ] Many species exhibit density-dependent dispersal and habitat selection. An initial argument against this hypothesis is that when a species colonizes formerly empty habitats, the average abundance of that species across all occupied habitats drops, negating an O—A relationship.
However, all species will occur at low densities in some occupied habitats, while only the abundant species will be able to reach high densities in some of their occupied habitats. Thus it is expected that both common and uncommon species will have similar minimum densities in occupied habitats, but that it is the maximum densities obtained by common species in some habitats that drive the positive relationship between mean densities and AOO. If density-dependent habitat selection were to determine positive O—A relationships, the distribution of a species would follow an Ideal Free Distribution IFD.
Metapopulation dynamics[ edit ] In a classical metapopulation model, habitat occurs in discrete patches, with a population in any one patch facing a substantial risk of extinction at any given time. Because population dynamics in individual patches are asynchronous, the system is maintained by dispersal between patches e.
However, there is currently debate regarding how many populations actually fit a classical metapopulation model. Vital rates[ edit ] The vital rates of a species in particular r — the intrinsic rate of increase; see Population dynamics interact with the habitat quality of an occupied patch to determine local density, and in multiple patches, can result in an O—A relationship.
In this system the population size within any given habitat patch was a function only of birth and death rates. By causing habitat quality to vary increasing or decreasing birth and death rates Holt was able to generate a positive intraspecific O—A relationship. Because the AOO and total abundance covary, an intraspecific occupancy abundance relationship is expected under situations where habitat quality varies through time more or less area above Hcrit.
Explaining the occupancy—abundance relationship[ edit ] Most of the different explanations that have been forwarded to explain the regularities in species abundance and geographic distribution mentioned above similarly predict a positive distribution—abundance relationship. This makes it difficult to test the validity of each explanation.
A key challenge is therefore to distinguish between the various mechanisms that have been proposed to underlie these near universal patterns. The effect of either niche dynamics or neutral dynamics represent two opposite views and many explanations take up intermediate positions.
Neutral dynamics assume species and habitats are equivalent and patterns in species abundance and distribution arise from stochastic occurrences of birth, death, immigration, extinction and speciation. Modelling this type of dynamics can simulate many of the patterns in species abundance including a positive occupancy—abundance relationship.
This does not necessarily imply niche differences among species are not important; being able to accurately model real life patterns does not mean that the model assumptions also reflect the actual mechanisms underlying these real-life patterns.
In fact, occupancy—abundance relationship are generated across many species, without taking into account the identity of a species. Therefore, it may not be too surprising that neutral models can accurately describe these community properties. Niche dynamics assume differences among species in their fundamental niche which should give rise to patterns in the abundance and distribution of species i.
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In this framework, the abundance and distribution of a single species and hence the emergent patterns across multiple species, are driven by causal mechanisms operating at the level of that species. Therefore, examining how differences between individual species shape these patterns, rather than analyzing the pattern itself, may help to understand these patterns.
Neutral dynamics may be relatively important in some cases, depending on the species, environmental conditions and the spatial and temporal scale level under consideration, whereas in other circumstances, niche dynamics may dominate. Thus niche and neutral dynamics may be operating simultaneously, constituting different endpoints of the same continuum.
Implications[ edit ] Important implications of both the intra- and interspecific O—A relationships are discussed by Gaston et al. For example, Zuckerberg et al. Using a dipswitch test with 15 criteria, Hui et al. Models based on the scaling pattern of occupancy i.
Given a positive intraspecific O—A relationship, it would be expected that with decreases in abundance there would be a decrease in range size, further increasing the potential for overharvesting. Conservation biology — The existence of positive intraspecific O—A relationships would exacerbate the risks faced by imperilled species.
Not only would reductions in range size and number of sites occupied directly increase the threat of extinction, but extinction risk would be further increased by the concurrent decline in abundance.
Importance of the interspecific O—A relationship[ edit ] Biodiversity inventory — An interspecific O—A relationship implies that those species that have a restricted distribution and hence will be important for conservation reasons will also have low abundance within their range.
Thus, when it is especially important that a species be detected, that species may be difficult to detect.
In effect, an intensive survey of a few sites will miss species with restricted distribution occurring at other sites, while an low-intensity extensive survey will miss species with low densities across most sites.
Conservation — As with the intraspecific relationship, the interspecific O—A relationship implies that species will not only be at risk of extinction due to low abundance, but because species with low abundance are expected to have restricted distributions, they are at risk of local catastrophe leading to global extinction. This may be confounded by the difficulty in surveying locally rare species due to both their low detectability and restricted distribution see above.
Finally, because rare species are expected to have restricted distributions, conservation programmes aimed at prioritizing sites for multi-species conservation will include fewer habitats for rare species than common species.