Evenness is a measure of the relative abundance of the different species making up the richness of an area. Plant community properties, such as species richness number of species, evenness abundance equality of species, and composition identity of species, affect key ecosystem functions, including ecosystem stability tilman and downing, 1994, resilience naeem et al. Another measure of species diversity is the species evenness, which is the relative abundance with which each species is represented in an. Simulated geographic variations of plant species richness. In this study, the relationship between phytoplankton evenness, species richness and biomass and the abundance of copepods was analyzed using data from lake nansihu, which is a typical lake in north china containing a significant abundance of both phytoplankton and copepods. Biodiversity loss degrades ecosystem functionality, and. As a general trend, mean species richness, species abundance, and species diversity was higher for the underarm microbe samples, compared to the inner elbow microbe samples across all datasets fig.
Species abundance refers to the number of individuals per species. In general, ecological communities with greater species richness will also result in samples that have greater evenness. And so, some of them are more abundant, in general, than the others. After ranking and plotting species, we see that both rankabundance curves extend equally far to the right, indicating equal species richness. All these measures rely on species concepts that are relatively straightforward in macroscopic organisms such as plants and animals, but are strongly debated in microbial taxa. A relationship between species richness and evenness. Keywords index, diversity, fractal theory, species abundance distribution introduction the relationship between species richness s, the number of species in a community and evenness e, the equitability of the proportional abundances of species remains an unsettled issue in current ecology tuomisto, 2012. Species diversity was more positively correlated with evenness than with richness among grasshoppers and flowering plants, in contrast to the other taxonomic. Species richness refers to the number of species in an area. A similar plot of rank abundance curves for lizard. An ecosystem where all the species are represented by the same number of individuals has high species evenness.
Introduction, simpsons index and shannonweiner index. Species diversity is a combination of species richness and species abundance. Intercropping with aromatic plants decreases herbivore. So the distribution of individuals among species is just the measure of evenness. Species richness variety of species or the number of different species or genera, families, etc.
These diversity measures are hypothesized to be positively and strongly correlated, but this null hypothesis has. But if there are 40 foxes and 42 dogs, the community is quite even. Evenness is the equitability of the species abundance distribution. Species richness has varieties of patterns that can be observed at any levels of research like in biogeography, evolutionary biology and ecology. Species diversity is determined not only by the number of species within a biological communityi. Due to the confounding of richness and evenness in the shannon index, many. 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. The importance of species diversity to the ecosystem. Community a has lower evenness than community b, which is indicated by the steeper slope of community a. If an ecosystem has poor species diversity, it may not function properly or efficiently. The methods on offer range from the familiar, such as the calculation of various diversity indices and the fitting of common distributions, to more recentlydeveloped techniques such as total species complement estimators. Richness, the compliment to simpsons d, and shannons h are computed for both stands. Species abundance distributions and richness estimations in.
Species abundance distributions and richness estimations. Evenness is considered as the measure of equality of abundances in a community. What is the difference between species richness and species. Species abundance and diversity flashcards quizlet. How species richness and total abundance constrain the distribution of abundance. Species richness, species abundance and species diversity. Species richness the simplest way to describe a community is to. In the abundance distribution graph, richness can be compared on the xaxis and evenness by the shape of the distribution. A relationship between species richness and evenness that. Difficult to define because definition consists of two distinct components. Community a is dominated by one of its 5 species and so has lower species diversity thancommunity b, which has the same 5 species but in equal proportion. To test the effect of habitatforming species evenness, richness, identity, and abundance on associated species, artificial communities were assembled in situ in the intertidal zone tidal height between 0. Rank abundance graphs and habitat suitability index. Problems in the measurement of evenness in ecology jstor.
Twentyfour indices of species diversity, richness and equitability evenness have. The proportion of species i relative to the total number of species p i is calculated, and then multiplied by the natural logarithm of this proportion lnp i. Sep 15, 2016 whats the difference between species richness and biodiversity. Biogeographic region biogeographic region components of species diversity. Plant community properties such as species richness, evenness, and. Department of biology, utah state university, logan, ut, 84322 usa. Simulated geographic variations of plant species richness, evenness and abundance using climatic constraints on plant functional diversity. This chapter studies attempts to make both concepts precise using mathematical approaches. Species diversity is a term used to define the different number of species in an area species richness and its abundance and the distribution of these species in that ecosystem. How do species richness and relative abundance of species.
A game reserve with one antelope and one zebra when compared with another. Which level of biodiversity includes species richness and. Parts of this chapter in particular, some of the introduction, parts of the nontechnical discussion of richness in sect. For example, in the image below, we can see that these two communities are composed of the same species and are identical in regards to species richness. Species evenness refers to how close in numbers each species in an environment is. Aug 01, 2012 intercropping significantly increased predator abundance and species richness by 18. What is the difference between species richness and. The number of marine species recorded per beach transect survey ranges between 1 and 30. Species diversity differs from species richness in that it takes into account both the numbers of species present and the dominance or evenness of species in relation to one another. A diverse species assemblage also contributes to ecosystem diversity. If you have only a few species in an habitats the species richness will be low and if there are a lot the species richness will be hight. Species evenness a comparison of the relative abundance of. Species abundance models describing communities there are two important descriptors of a community.
A diversity index is a mathematical measure of species diversity in a community. Whats the difference between species richness and species. Two communities may be equally rich in species but differ in relative abundance. Further, speciesabundance distributions relate to species diversity in that more even or. Species richness an index based on the number of species i. Ecologists call the number of species in an area its richness, and the relative abundance of species its evenness. But independently of the richness, the eveneness is comparing the number of individuals between species. A common approach is to plot some measure of species abundance against their rank order of abundance. Geographic patterns indicate higher species richness in tropical regions than in polar region wherein rainforest and coral reefs considered as the most speciesrich habitat found in the tropical regions. Such a plot allows the user to compare not only relative richness but also evenness. Furthermore, herbivore abundance and species richness were strongly negatively correlated with predator species richness. Species richness and evenness were uncorrelated or weakly negatively correlated for each taxonomic group, supporting the conclusion that richness alone is an incomplete measure of diversity. For example, each community may contain 5 species and 300 individuals, but in one community all species are equally common e.
This is rare that all the species are equally abundant. Species richness means the variability number of species within a region ec. Another approach to measuring diversity is to fit a species abundance distribution, or use a parameter of a distribution, most famously log series a, as a diversity measure. Species abundance distribution can also be expressed through rank abundance graphs. Plant community properties, such as species richness number of species, evenness abundance equality of. The relationship between phytoplankton evenness and. Other articles where species abundance is discussed. The quiz will test you on the definitions of key terms related to species richness.
Draw a bar graph that illustrates the relationship between fire return interval and species richness. Species abundance is the number of individuals per species, and relative abundance refers to the evenness of distribution of. Sep 23, 2016 species diversity is a term used to define the different number of species in an area species richness and its abundance and the distribution of these species in that ecosystem. The shannon diversity index h is another index that is commonly used to characterize species diversity in a community.
Species richness the number of different species in a particular area species evenness the relative abundance with which each species are represented in an area. These two diversity indices incorporate both richness and evenness. The log transformed abundance means had the lowest pvalue of 0. Nov 09, 2012 the relationships between empirical species richness s and evenness j.
Bi which incorporates measures of sand particle size, slope, and tide range therefore shows a very close. Species diversity and richness 4 is designed for professional ecologists and their students. Species richness ridge 2030 19 slope 5060 39 valley 100120 24 a. According to the encyclopedia of earth, species diversity is a measurement of an ecosystems species richness and species evenness.
Although many ecologists focus on the relationship between species richness s and evenness e, conflicts between observation and theory are difficult to reconcile. When taking spatial scale into account, in the natural community, these. The ace abundancebased covera ge estimator of species richness is based on the concept of sample coverage or simply coverage, which was originally. The relationship between species richness and evenness in.
The questions will either provide you with a term or definition. Species richness is sometime considered synonymous with species diversity, but the formal metric species diversity takes into. Species richness is the number of different species represented in an ecological community, landscape or region. Magurran 1988 commented that by looking at the fully species abundance distribution it is possible to get a better picture of the relationship between species richness s and evenness e. Empirical relationships between species richness, evenness. Relative species abundance is how common a species is relative to the other species in a defined location. Effects of habitatforming species richness, evenness.
Since e essentially depended on the relative abundance distribution rad, the hypothesis of this paper was. The relationships between empirical species richness s and evenness j. The species richness is how much species there are in an area. As a measure of species diversity, we will calculate the shannon index, h. Traditional attempts to define biodiversity consider two components. The diversity of species in a particular area depends not only the number of species found, but also in their numbers. Table shows the abundance of species number of individuals per hectare in three ecosystems and gives the measures of species richness s, evenness e, and the shannon diversity index h.
Species abundance is the number of individuals per species, and relative abundance refers to the evenness of distribution of individuals among species in a community. Intercropping significantly increased predator abundance and species richness by 18. How species richness and total abundance constrain the. The diversity of species in an area depends on both the number of species observed species richness and their total numbers, and evenness refers to the relative abundance of species. The species diversity and richness version 4, first released in january 2006, includes the following additions and enhancements. Relationships between species richness, evenness, and abundance. So if there are 40 foxes and dogs, the community is not very even. Species richness is the number of species present in a sample, ecological community, ecosystem, landscape, region, or any defined spatial unit. Pdf species richness and evenness respond in a different manner. A total of 56 polyethylene experimental grids were screwed to the bedrock with a flat surface 30.
Species richness, the number of species recorded per transect survey, increases in response to decreasing sand particle size, flattening beach face slope, and increasing tide range figure 7. Richness number of species evennessrelative abundance. Species richness definition and examples biology online. On the other hand, species diversity is a function of the number of species present i. Mathematically it is defined as a diversity index, a measure of biodiversity which quantifies how equal the community is numerically. An ecosystem where some species are represented by many individuals, and other species are represented by very few individuals has a low species evenness. However, mean differences were not significant table 2. A game reserve with one antelope and one zebra when compared with another with one antelope and ten zebra, therefore, have same species richness but different species evenness. In each case, richness was positively correlated with one or more measures of abundance. Like simpsons index, shannons index accounts for both abundance and evenness of the species present. Although various types of such relationships have been proposed may, 1975. Diversity indices provide more information about community composition than simply species richness i. The importance of species diversity to the ecosystem sciencing. A comparison of species richness, abundance, and diversity.