Species richness

Species richness is the number of different species represented in an ecological community, landscape or region.^[1] Species richness is simply a count of species, and it does not take into account the abundances of the species or their relative abundance distributions. Species richness is sometimes considered synonymous with species diversity, but the formal metric species diversity takes into account both species richness and species evenness. Species richness has proven to be a positive representation to show how species interaction in ecosystems can lead to the productivity and growth of biodiversity. ^[2]

Depending on the purposes of quantifying species richness, the individuals can be selected in different ways. They can be, for example, trees found in an inventory plot, birds observed from a monitoring point, or beetles collected in a pitfall trap. Once the set of individuals has been defined, its species richness can be exactly quantified, provided the species-level taxonomy of the organisms of interest is well enough known. Applying different species delimitations will lead to different species richness values for the same set of individuals.

In practice, people are usually interested in the species richness of areas so large that not all individuals in them can be observed and identified to species. Then applying different sampling methods will lead to different sets of individuals being observed for the same area of interest, and the species richness of each set may be different. When a new individual is added to a set, it may introduce a species that was not yet represented in the set, and thereby increase the species richness of the set. For this reason, sets with many individuals can be expected to contain more species than sets with fewer individuals.

If species richness of the obtained sample is taken to represent species richness of the underlying habitat or other larger unit, values are only comparable if sampling efforts are standardized in an appropriate way. Resampling methods can be used to bring samples of different sizes to a common footing.^[3] Properties of the sample, especially the number of species only represented by one or a few individuals, can be used to help estimating the species richness in the population from which the sample was drawn.^[4][5][6] These indications and adaptations to the detail of population enhancements can provide further diversity in urban ecological areas by means of promoting species richness while also considering the ecological community.

The observed species richness is affected not only by the number of individuals but also by the heterogeneity of the sample. If individuals are drawn from different environmental conditions (or different habitats), the species richness of the resulting set can be expected to be higher than if all individuals are drawn from similar environments. The accumulation of new species with increasing sampling effort can be visualized with a species accumulation curve. Such curves can be constructed in different ways.^[7] Increasing the area sampled increases observed species richness both because more individuals get included in the sample and because large areas are environmentally more heterogeneous than small areas.

Many organism groups have most species in the tropics, which leads to latitudinal gradients in species richness. There has been much discussion about the relationship between productivity and species richness. Results have varied among studies, such that no global consensus on either the pattern or its possible causes has emerged.^[8] Species diversity and richness is likely to occur in areas of warmer climates because of variability in food types, mating opportunities, urban area provision of cleaner environments and other factors that can lead to an improved species richness.^[9]

Species richness also depicts immense extension by means of expanding in terms of ecological and environmental availability of urban food types which enriches the likelihood of species richness increasing even in urban areas; additionally, increasing food availability in certain environments will provide better chances of species richness in terms of diversity. ^[10] Where there is food, there are animals according to the balance of nature or the ecological balance as it is generally known, ^[11] which expresses types of food chain and food webs which are both used in urban ecology to show the differences but mostly similarities in which feeding relations between species can be understood.^[12] Every type of species will consist of their individual type of feeding relationship with organisms provided by the environment,^[13] however, it is necessary to understand that feeding relationships and the urban species will indeed form a type of symbiotic relationship within an ecosystem according to urban necessities as shown in the image provided.^[14]

Species richness is often used as a criterion when assessing the relative conservation values of habitats or landscapes. However, species richness is blind to the identity of the species. An area with many endemic or rare species is generally considered to have higher conservation value than another area where species richness is similar, but all the species are common and widespread.

Location-wise, urban settings can influence species richness by means of proper environmental conservation, availability of safety and other factors like water, trees, and sustainable habitat. Species thrives in areas where they are provided with the basic necessities for their survival, even in urban areas where they may face challenges like competition or predators, they still have a high chance of surviving when placed in an environment that provides adequate resources that can benefit the species and promote species diversity and richness.^[15]

• Rapoport's rule
• Scaling pattern of occupancy
• Species-area curve
• Species discovery curve
• Storage effect

Scholia has a profile for species richness (Q17146659).

• Kevin J. Gaston & John I. Spicer. 2004. Biodiversity: an introduction, Blackwell Publishing. 2nd Ed., ISBN 1-4051-1857-1(pbk.)
• Diaz, et al. Ecosystems and Human Well-being: Current State and Trends, Volume 1. Millennium Ecosystem Assessment. 2005. Island Press.