It describes the general pattern of increase in species richness with increasing area of observation, but it can take on different forms. Introduction: The relationship between island area and number of species is well diversity patterns have important implications for conservation of biodiversity. Species-area relationships are a common focus of habitat fragmentation research .. The relationship between species richness and area is well known in.
Furthermore the relationship between species richness and evenness can vary with change in key ecological processes such as competition, predation, and succession, each of which can alter proportional diversity through changes in evenness without any change in species composition . Hence some authors suggest that we should treat the two main components of diversity separately in investigating the determinants of diversity .
Therefore, understanding the patterns and the mechanisms that determine the relationship between species richness and evenness can provide important information on biodiversity maintenance . However the relationship between species richness and evenness across local communities remains a controversial issue in ecology because of the wide variation in both of empirical and theoretical patterns that have been reported .
Several theoretical studies have assumed that species richness and evenness should be independent or positively correlated.
These studies date back to DeBenedictis  who argued that mathematical relationships between measures of diversity such as species richness and evenness constrain the correlations among these measures and that they should therefore be strongly and positively correlated. Similar predictions of strong and positive relationships among measures of community diversity have been made by other theoretical studies .
More recent investigations by Jost  suggest what DeBenedictis  had earlier pointed out — that species richness and species evenness are not independent components of community diversity and that the correlation is constrained by the underlying mathematical relationships.
Jost  then proceeds to argue that we should consider a relative measure of evenness relative to the maximum possible value for a given species richness in comparative analysis of communities.
Species–area relationship - Wikipedia
Nevertheless, many studies have assumed that species richness and evenness are two independent indices . Empirical studies of the relationship between species richness and evenness have also reported contrasting findings.
Earlier observational research suggested that species richness was positively correlated with evenness .
More recently other empirical studies indicate that species richness and evenness are strongly negatively  or independently  associated in plant communities. These contrasting theoretical arguments and empirical findings cannot be easily reconciled. We there need more research on the relationship between richness and evenness along different geographical gradients and in different communities across the world.Tommaso Jucker - Relationship between Productivity and Species Diversity
Here we propose to investigate the relationship between richness and evenness in species-rich sub-alpine meadow communities in the Qinghai Tibetan plateau. We can also plot the log10 of species number against the log10 of the distance of the islands from the Florida mainland. The relationship between the log10 of the species number and the log10 of island area clearly shows an increasing trend, and is well-approximated by the linear form of the model.
Similarly, a decreasing trend of species number with island distance can be seen from the second graph. Whether or not the number of species is at equilibrium is less clear; interpretation of the data regarding this question is made more difficult by uncertainty about the history of sea-level changes over the past 10, years.
Both island size and distance from the mainland are associated with the number of species present. In general, it has been found that the relationship between island area and number of species present is fairly constant for islands in a given geographic region.
In this way it is possible to make potentially useful predictions about the number of species on islands or habitat islands when little information other than size is available.
For conservation planning, knowledge of this relationship is of utmost importance. An excellent historical review is provided in McGuinnesswhich connects debates over the form and function of species-area relationships with emerging ecological theory.
Connor and McCoy also reviews the evidence linking species-area relationships to biological and ecological explanations, but the authors focus on the statistical validity of attempts to use the form and parameters of species-area curves to discern ecological causality. Rosenzweig explores in detail several examples of species-area curves and uses them to discuss the many factors that influence the shape of these curves, while Drakare, et al.
Because of the variety of research goals inherent in studies of species-area relationships, sampling and analytical methods, as well as definitions of what constitutes a species-area relationship, often vary among studies. Scheiner defines six types of species-area curves that differ in the spatial arrangement of samples, whether larger samples are constructed in a spatially explicit fashion from adjacent smaller samples, and whether means or single values are used for a given spatial scale.
The statistics and biology of the species-area relationship. Which function describes the species-area relationship best?
A review and empirical evaluation. Journal of Biogeography The author recognizes only nested, spatially explicit, and island curves as true species-area relationships because each point in the curve is internally contiguous.