Briefly explain the relationship that Hylander and Ehrlen 2015 propose between p

Question

Briefly explain the relationship that Hylander and Ehrlen 2015 propose between patch occupancy and habitat quality/quantity/connectivity (i.e. Figure 2), with respect to extinction debt.

Size of extinction debts (A occupancy) te species b Size of extinction debt A occupancy) at t t species a habitat quality/quantity/connectivity habitat quality/quantity/connectivity habitat quality/quantity/connectivity habitat quality/quantity/connectivity TRENDS in Ecology& Evolution Figure 2. Size and duration of extinction debts as a function of habitat change. (a) Occupancy for a species in terms of the number of populations in the focal area at different times as a function of habitat change. to is the time at which the habitat has just changed before any extinctions has taken place; t and tx are different time intervals after habitat change; and te is the time at which a new equilibrium is reached, that is, when all extinctions have occurred. (b) Two examples of different occupancy versus habitat change relationships. The upper (red) curve illustrates a situation in which a small habitat change leads to only small changes in occupancy, whereas greater changes lead to a more rapid decrease in occupancy. The lower (blue) curve shows a species that is sensitive to small changes. (c) Size of the extinction debt (delta occupancy) as a function of habitat change. (d) Expected mean time to extinction as a function of habitat change. The thin lines in (c) and (d) illustrate that many monotonic relationships are possible

Explanation / Answer

Population viability can depend on habitat area, habitat quality, the spatial arrangement of habitats (aggregations and connections) and the properties of the intervening non-breeding (matrix) land. extinction debt is the future extinction of species due to events in the past. Extinction debt occurs because of time delays between impacts on a species, such as destruction of habitat, and the species' ultimate disappearance.

The time-delayed extinction of plant species following habitat fragmentation is a well-known phenomenon in ecology. The length of the relaxation time until this ‘extinction debt’ is paid (i.e., until extinctions cease) depends on the ecosystem, species group and extent of fragmentation.

Changes in species richness along the ecological succession gradient may be strongly determined by coexisting extinction debts of species from the original habitats and colonization credits of those from the replacing habitats. The magnitude of these processes and their causes remain largely unknown. the extinction debt and colonization credit for grassland and forest specialist plants, respectively, and the local and landscape factors associated to the richness of these species groups in a 50-year process of forest encroachment into semi-natural Mediterranean grasslands.

A set of sampling plots of persistent grasslands and forests and their transitional habitat (wooded grasslands) was selected within fixed-area sites distributed across the landscape results confirm the extinction debt and suggest colonization credit (according to observed trends and model predictions) in wooded grasslands when compared to persistent forests, despite wooded grasslands and persistent forests having similar tree cover. Grassland connectivity and solar radiation had opposing effects on the richness of both grassland and forest specialists, and it is possible that the availability of seed sources from old forests may have accelerate the payment of colonization credit in the wooded grasslands. These results suggest that extinction debt and colonization credit have driven species turnover during the 50 years of forest encroachment, but at different rates, and that local and landscape factors have opposing effects on these two phenomena. They also highlight the importance of documenting biodiversity time lags following habitat change when they are still in progress in order to timely and adequately manage habitats of high conservation value such as the grasslands.

Extinction debts can result from many types of habitat changes involving mechanisms other than metapopulation processes.

Extinction debts can arise because

A failure to distinguish between these different mechanisms and to simultaneously consider both the size of the extinction debt and the relaxation time hampers our understanding of how extinction debts arise and our ability to prevent ultimate extinctions.

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