The Theory of Island Biogeography posits that the number of species on an island is a balance between immigration and extinction rates. Larger islands can support larger populations and more diverse habitats, reducing extinction risk, while islands closer to a mainland have higher immigration rates.
Habitat Heterogeneity refers to the physical complexity of an environment, such as variations in topography, soil types, or vegetation layers. A more complex environment provides more 'niches' or specialized roles, allowing more species to coexist without directly competing for the same resources.
Fragmentation occurs when large, continuous habitats are broken into smaller, isolated patches, often due to human activity. This reduces the total area available and increases 'edge effects,' where the perimeter of a habitat is exposed to different environmental conditions that may be unsuitable for interior-dwelling species.
The Intermediate Disturbance Hypothesis (IDH) suggests that local species diversity is maximized when ecological disturbance is neither too rare nor too frequent. At low levels of disturbance, competitive dominants exclude other species; at high levels, only the most stress-tolerant species survive.
Keystone Species have a disproportionately large effect on their environment relative to their abundance. By controlling the population of prey or modifying the physical environment, they prevent a single species from dominating and thus maintain higher overall biodiversity.
Niche Partitioning is a process where competing species use the environment differently in a way that helps them coexist. This might involve feeding at different times of day, occupying different heights in a forest canopy, or consuming different sizes of prey.
| Metric | Definition | Focus |
|---|---|---|
| Alpha Diversity | Diversity within a single local site or ecosystem. | Local richness |
| Beta Diversity | The variation in species composition between two sites. | Species turnover |
| Gamma Diversity | The total regional diversity across all ecosystems. | Landscape richness |
Identify the Scale: When asked about biodiversity, determine if the question refers to genetic, species, or ecosystem levels. Misidentifying the scale often leads to incorrect conclusions about the factors involved.
Analyze the Gradient: If a problem involves geographic data, always check for latitude and altitude. Biodiversity typically decreases as you move away from the equator or higher up a mountain due to harsher conditions and lower energy availability.
Disturbance Logic: Remember that 'disturbance' is not always negative. In exam scenarios involving the Intermediate Disturbance Hypothesis, look for the 'sweet spot' where moderate change prevents competitive exclusion without wiping out the community.
Check for Connectivity: When evaluating habitat loss, look for the presence of 'wildlife corridors.' Even if total area is reduced, connectivity can mitigate some loss of biodiversity by allowing gene flow between isolated populations.
