[5] Extinction debt is also known by the terms dead clade walking and survival without recovery[1] when referring to the species affected.
However, as other patches have been destroyed or rendered inaccessible due to fragmentation, this "insurance" effect is reduced and the species may ultimately become extinct.
His analysis focused on marine molluscs since they constitute the most abundant group of fossils and are therefore the least likely to produce sampling errors.
Jablonski suggested that two possible explanations deserved further study: The time to "payoff" of extinction debt can be very long.
Islands that lost habitat at the end of the last ice age 10,000 years ago still appear to be losing species as a result.
[5] It has been shown that some bryozoans, a type of microscopic marine organism, became extinct due to the volcanic rise of the Isthmus of Panama.
[15] Tilman et al. demonstrated that extinction debt could occur using a mathematical ecosystem model of species metapopulations.
Tilman et al. used this model to predict that species would persist long after they no longer had sufficient habitat to support them.
This has been one of the more controversial components of the model, as there is little evidence for this trade-off in many ecosystems, and in many empirical studies dominant competitors were least likely species to become extinct.
[16] A later modification of the model showed that these trade-off assumptions may be relaxed, but need to exist partially, in order for the theory to work.
For instance, habitat destruction resembling slash-and-burn agriculture is thought to affect rare species rather than poor colonizers.
Models derived from neutral theory have successfully predicted extinction times for a number of bird species, but perform poorly at both very small and very large spatial scales.
[19] Mathematical models have also shown that extinction debt will last longer if it occurs in response to large habitat impacts (as the system will move farther from equilibrium), and if species are long-lived.
Finally, extinction debts are predicted to last longer in landscapes with a few large patches of habitat, rather than many small ones.
Processes that drive extinction debt are inherently slow and highly variable (noisy), and it is difficult to locate or count the very small populations of near-extinct species.
For instance, in the Amazon rainforest, researchers have measured the rate at which bird species disappear after forest is cut down.
If this prediction is lower than the actual number of species in the cleared habitat, then the difference represents extinction debt.
Studies of European grasslands show evidence of extinction debt through both comparisons with the past and between present-day systems with different levels of human impacts.
The species diversity of grasslands in Sweden appears to be a remnant of more connected landscapes present 50 to 100 years ago.
[24] Forests in Flemish Brabant, Belgium, show evidence of extinction debt remaining from deforestation that occurred between 1775 and 1900.
[25] Extinction debt has been found among species of butterflies living in the grasslands on Saaremaa and Muhu – islands off the western coast of Estonia.
[28] Birds in the Amazon rainforest continued to become extinct locally for 12 years following logging that broke up contiguous forest into smaller fragments.