Habitat loss Flashcards
(8 cards)
What is the main driver of habitat loss and where is most likely to see future habitat loss?
Land conversion for agriculture is the main driver of habitat loss, due to human population growth and diet changes putting pressure on the food system. Marginal areas in tropical and less developed parts of the world are where land conversion is happening most, as developed / populated areas have already converted a large fraction of their available land to cropland.
How can the relationship between species richness and area be represented?
S = c * A^z
Where S is species richness, A is area, c is the number (fitted constant) of species within one unit of area, and z is the rate of increase.
This relationship can be linearised as follows, and / or plotted as a species-area curve.
log(S) = log(c) + [z * log(A)]
What causes higher species richness in larger areas?
Larger areas contain a greater variety of habitat types and heterogeneity and can support larger populations, which are then less likely to go extinct compared to small populations. In addition, larger areas contain more individuals meaning that a higher species richness can be found when sampling.
Why do fragmented habitats have lower species richness than similar areas of contiguous habitat?
Habitat fragmentation reduces species richness because the sub-populations may become isolated and be more likely to go extinct, species with large home ranges may not be able to be supported within the remaining fragments, and the proportion of edge increases, leading to stronger edge effects.
What is the matrix and how can its properties influence the response to fragmentation?
The matrix is the area or type of land that joins up the patches of fragmented habitat. If the matrix is inhospitable, sub-populations will become isolated and be more likely to go extinct. If the matrix contrasts a lot compared to the original habitat, it becomes less likely that species can utilise the matrix area. If the matrix is, for example, a road, this can increase mortality as well as acting as a barrier to movement.
Explain edge effects and how fragment shape can influence them.
At the edge of habitats, the physical environment is often different and species from the matrix may infiltrate into the habitat and predate / outcompete other species. Some species may respond differently to the edge habitat, leading to lower diversity and biased species composition. Long, thin and irregular shapes of fragments increase the edge:area ratio and so experience greater influence of edge effects.
What is relaxation in terms of fragmentation?
Relaxation refers to the continued loss of species in remnant fragments from an original species pool to a reduced species pool after fragmentation. Even if fragmentation is stopped early on, the decline in species continues for a considerable time - this is called an extinction debt.
How might different species be affected by habitat fragmentation differently?
Fragmentation disproportionately affects species that are naturally rare, have wide ranges, are short-lived, have low fecundity (produce few offspring), and are limited in terms of dispersal. Some species may benefit from the fragmentation if they thrive in the edge habitat. This results in a biased or nested subset of the original community.
