Ecological Concepts: Species Richness, Diversity, and Community Dynamics
Species Richness, Diversity, and Abundance
Species Richness
Species richness refers to the number of different species present in a community. It does not consider the relative abundance of each species.
Diversity Indices
Diversity indices combine species richness with the evenness of species distribution. They provide a more comprehensive measure of community diversity.
Species Abundance Diagrams
Species abundance diagrams graphically represent the distribution of species abundance within a community. They can reveal patterns such as dominance by a few common species or a more even distribution of abundance.
Paradox of Enrichment
The paradox of enrichment states that increased productivity can lead to the extinction of some species due to competitive exclusion. This can be analyzed using graphs that plot species richness against productivity indices.
Predation and Species Richness
Predation can have contrasting effects on species richness:
- Positive effect: Predation can reduce interspecific competition, allowing prey species to coexist with each other and their predators (predator-mediated coexistence).
- Negative effect: Intense predation can drive prey species to extinction, reducing species richness.
Intermediate Disturbance Hypothesis
The intermediate disturbance hypothesis states that communities with intermediate levels of disturbance have higher species richness. This is because disturbances create opportunities for new species to establish, while preventing any one species from dominating.
Insular Habitats
Insular habitats are isolated areas that resemble islands, such as:
- Pools of water
- Forest fragments
- Lakes
- Mountain peaks
- Isolated trees in savannas
- Gaps in forests
- Private lands
- Areas with distinct vegetation surrounded by different types of rock, soil, or vegetation
Island Biogeography Theory
An experiment on mangrove islands in Florida Bay showed that reducing island size did not decrease arthropod species richness. This suggests that habitat diversity, rather than island size, may be a more important factor in determining species richness.
Ripple Effect and Species Richness
The ripple effect is a process where one ecological change triggers a series of subsequent changes. It can be applied to explain the increase in species richness during community succession and the latitudinal gradient of species richness.
From the poles to the tropics, species richness increases due to factors such as predation, productivity, climate variation, and evolutionary age. These factors interact in a ripple effect, where each change triggers another, leading to an overall increase in species richness.