What type of distribution is most common in nature

The distribution of species depends upon various biotic and abiotic factors. The distribution pattern can change seasonally, in response to the availability of resources and also depending upon the scale at which they are viewed. Various factors like speciation ,extinction, continental drift, glaciation, variations of sea levels, river capture, and available resources are useful in understanding species distribution.

What is species distribution? Biology The Elements of an Ecosystem Species. Linica Uday. The density of organisms varies depending on a variety of factors. Deaths, births, immigration, and emigration are all processes that can impact population density at a given time. However, there are general trends associated with density.

For example, across a number of species, smaller organisms tend to occur at higher densities than larger organisms White et al. Although our understanding of these processes and patterns associated with density has improved, there is still an enormous amount of descriptive and experimental work needed to understand how organismal characteristics are associated with density Blackburn et al. How individuals are arranged in space can tell you a great deal about their ecology.

For instance, Figure 1 shows the distribution of a hypothetical species. Most people would describe this as a random pattern in space. However, if you look closely you will notice that individuals are not actually randomly distributed, they are maintaining a fairly uniform distance between each other. Why do you think that is? Figure 2 shows the distribution of another hypothetical species. This time they are grouped together in certain 5 x 5 meter areas but not in others. What might this tell you about this species and its interactions with the environment?

Figure 3 shows the distribution of individuals of a hypothetical species that is actually random. One thing that you'll notice is that it is difficult to think of this as random! Figure 1: Clumped dispersion of individuals The average number of individuals per square is 6. These three figures illustrate the three different patterns of dispersion that ecologists observe. Clumped dispersion Figure 1 where individuals are aggregated in certain areas of the sampled space.

Uniform dispersion Figure 2 , where individuals are almost equally spaced apart from each other and random dispersion Figure 3. Figure 2: Uniform dispersion of individuals The average number of individuals per square is 10, and the variance is 4.

The variance to mean ratio is 0. Behavioral and ecological factors influence dispersion. Uniform patterns of dispersion are generally a result of interactions between individuals like competition and territoriality.

Clumped patterns usually occur when resources are concentrated in small areas within a larger habitat or because of individuals forming social groups. At large spatial scales most organisms appear to have clumped distributions because their habitats are not uniformly distributed over wide areas. Although you might not think of plants as territorial, they too can have uniform dispersion patterns that are a result of territoriality and competition e.

Random dispersion patterns are atypical in nature and could indicate a uniform or random distribution of resources or a lack of interactions among individuals in the population. Figure 3: Random dispersion of individuals The mean number of individuals per square is 5.

Humans are not always very good at distinguishing among the different patterns of dispersion, so statistical methods are usually used to tell the difference between them. A very simple method that can be used to determine dispersion patterns is based on the sample mean and variance of the number of individuals counted in repeated quadrats in a particular area that is sampled. The sample mean is the average collected from the sample. As an example, let's examine Figure 1. This figure is divided into squares, and each square represents a sample of organisms in space.

In this case the organisms are clumped in space and there are 4 samples with 25 organisms and 12 with no organisms. Thus the mean number per square in Figure 1 is 6. The variance is calculated by squaring the differences between the sample mean and each of the observations, adding them up to produce the sum of the squares, and dividing by the sample size minus 1.

So the variance in this case would be [25 - 6. So in Figure 1 the average number of individuals per grid square is 6. The ratio of the variance to the mean can then be used to determine whether the pattern is uniform or clumped, and is referred to as the index of dispersion Krebs In this case the ratio is 20, which is much greater than 1! This indicates that individuals in this population are exhibiting a clumped spacing pattern in the sampled habitat.

If this ratio is less than one, it indicates a uniform distribution e. Concluding remarks. Cold Spring Harbor Symposium. Quantitative Biology 22, — Magurran, A. Explaining the excess of rare species in natural species abundance distributions. McGill, B. Species abundance distributions: Moving beyond single prediction theories to integration within an ecological framework. Ecology Letters 10, — Preston, F. The commonness, and rarity, of species. Ecology 29, — Sugihara, G.

Predicted correspondence between species abundances and dendrograms of niche similarities. Verberk, W. Explaining abundance-occupancy relationships in specialists and generalists: A case study on aquatic macroinvertebrates in standing waters. Journal of Animal Ecology 79, — Predation, Herbivory, and Parasitism. Characterizing Communities. Species with a Large Impact on Community Structure. Successional Changes in Communities.

Effects of Biogeography on Community Diversity. Community Ecology Introduction. Avian Egg Coloration and Visual Ecology.

Causes and Consequences of Biodiversity Declines. Disease Ecology. The Ecology of Avian Brood Parasitism. Elemental Defenses of Plants by Metals. The Maintenance of Species Diversity.

Neutral Theory of Species Diversity. Abiotically-Mediated Direct and Indirect Effects. Biological Stoichiometry. Sampling Biological Communities. Succession: A Closer Look. Dynamics of Predation. Ecological Consequences of Parasitism. Resource Partitioning and Why It Matters. Direct and Indirect Interactions. Keystone Species. Citation: Verberk, W.

Nature Education Knowledge 3 10 Aa Aa Aa. Figure 1: The commonness and rarity of species in a community. In nearly every community in which species have been identified and counted, distributions are highly skewed such that a few species are present in the greatest numbers.

Patterns in Species Abundance. Figure 2: Differences between communities in equitability of abundances. A Communities in salt marshes are species poor and characterized by a very skewed pattern in species abundance, possibly owing to periodic disturbance by seawater. Figure 3: Species abundance distributions on a log-normal scale.

The number of species plotted for different abundance intervals, each interval being twice the preceding one. Distribution-abundance Relationship. Figure 4: The interspecific distribution-abundance relationship. A Generally, a positive relationship results when plotting measures of abundance against measures of distribution for different species from a species group.

Figure 5: Explanations for a positive distribution-abundance relationship. A A positive feedback between local population size and regional distribution may generate a positive distribution-abundance relationship. As so often occurs in ecology, different explanations are not always mutually exclusive. In dynamic environments with pronounced environmental gradients e. In contrast, neutral dynamics may be the dominant force in less variable environments such as a community of tropical forest trees, where dispersal limitation and a long lifespan may prevent competitive exclusion.

Neutral dynamics may be relatively important in some cases, depending on the species, environmental conditions and the spatial and temporal scale 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. I have discussed two of the most robust patterns in community ecology: 1 the skewed pattern in species abundance, in which a community contains many rare species and only a few common species and 2 the positive distribution-abundance relationship, in which widespread species tend also to occur in high abundance throughout their range.

Understanding these patterns has important implications for practical issues like reserve selection and predicting extinction risk.

Two independent approaches seek to explain these emergent patterns. The first focuses on neutral dynamics with patterns in species abundance and distribution arising from stochastic occurrences of birth, death, immigration, extinction, and speciation. The second focuses on niche differences among species as the driving force behind the abundance and distribution of a single species, and hence the emergent patterns across multiple species.

Both may be operating simultaneously, constituting different endpoints of the same continuum. Chapter Sensory Systems. Chapter Musculoskeletal System. Chapter Endocrine System. Chapter Circulatory and Pulmonary Systems. Chapter Osmoregulation and Excretion. Chapter Immune System. Chapter Reproduction and Development. Chapter Behavior. Chapter Ecosystems. Chapter Biodiversity and Conservation. Chapter Speciation and Diversity. Chapter Natural Selection. Chapter Population Genetics.

Chapter Evolutionary History. Chapter Plant Structure, Growth, and Nutrition. Chapter Plant Reproduction. Chapter Plant Responses to the Environment. Full Table of Contents. This is a sample clip. Sign in or start your free trial. JoVE Core Biology. Previous Video Next Video. Embed Share. To understand the way that species interact with their environment and other species, a study called ecology. Please enter your institutional email to check if you have access to this content.

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