Diversity and Abundance

Absolute Abundance

refers to the specific number of individuals of a given species in a community

Relative abundance

(also known as species evenness) describes the proportion of individuals in a community represented by each species

Species Richness

This is the total number of different species found within a community. It provides a count of species but does not indicate how evenly individuals are distributed among those species

Rank Abundance Curves

These curves are visual tools used to compare the richness and evenness of different communities. On these graphs, the number of data points along the x-axis represents species richness, while the slope of the line reflects the species evenness

Environmental Complexity

This refers to the physical structure and variety of a habitat; generally, more complex environments (such as those with greater foliage height) lead to higher species diversity

Nutrient Availability

This is the presence of limiting resources that organisms require and compete for

Interestingly, the sources note a negative relationship between high nutrient availability (such as added nitrogen) and species richness, often due to competitive exclusion or eutrophication

Biodiversity Hotspot

These are specific areas of the world that contain exceptionally high numbers of endemic species, which are species found nowhere else on Earth

Island Equilibrium Model

Developed by MacArthur and Wilson, this model predicts that species richness on an island represents a balance between the immigration of new species and the extinction of established species

Species Area Effect

This is the principle that, all other factors being equal, larger geographic areas or habitats will contain more species

Disturbance

These are environmental events—ranging from natural occurrences like fires and storms to human-caused events like pollution—that vary in frequency and severity and affect the diversity of a community

Intermediate Disturbance Hypothesis

This hypothesis states that moderate levels of disturbance foster the greatest species diversity. High levels of disturbance exclude slow-growing species, while low levels allow dominant species to outcompete and exclude others