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. 2023 Jun 7;13(12):1907.
doi: 10.3390/ani13121907.

Empirical Evidence for the Rescue Effect from a Natural Microcosm

Richard M Lehtinen  1
Affiliations

Empirical Evidence for the Rescue Effect from a Natural Microcosm

Richard M Lehtinen. Animals (Basel). .

Abstract

Ecological theory predicts that populations which receive immigrants are less vulnerable to extinction than those that do not receive immigrants (the "rescue effect"). A parallel but opposite process may also exist, where emigration increases the risk of local extinction (the "abandon-ship effect"). Using a natural microcosm of plant-specialist frogs from Madagascar, empirical evidence for both processes is provided. Populations receiving immigrants were less extinction-prone than those without immigration, and those populations losing individuals through emigration were more extinction-prone than those in which no emigration occurred. The number of immigrants and emigrants was also elevated and depressed (respectively) in patches that did not go extinct. These data provide some of the first definitive empirical evidence for the rescue effect and provide suggestive initial data on the abandon-ship effect. Both of these processes may be important to understanding the dynamics of populations.

Keywords: Guibemantis; Pandanus; abandon-ship effect; dispersal; emigration; extinction risk; immigration; population ecology; rescue effect.

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Conflict of interest statement

The author declares no conflict of interest.

Figures

Figure 1
Figure 1
Adult Guibemantis wattersoni on a Pandanus leaf (left). Pandanus plant with three G. wattersoni (right). Photos by the author.
Figure 2
Figure 2
Patches experiencing extinction in a given year had a significantly smaller population size of G. wattersoni compared to patches that did not experience extinction (all years pooled, excluding unoccupied patches, Mann–Whitney test U = 9069.5, n = 380, p < 0.014). Error bars indicate means ± 2 SE.
Figure 3
Figure 3
(A) Mean number (±2 SE) of immigrants to patches that went extinct (‘yes’) and those that did not experience extinction (‘no’), pooled data from all years 2000–2002. Patches that went extinct had significantly fewer immigrants (t = 2.45, df = 187, p = 0.025). (B) Mean number (±2 SE) of emigrants to patches that went extinct (‘yes’) and those that did not experience extinction (‘no’), pooled data from all years 2000–2002. Patches that went extinct had relatively more emigrants on average but this was not a significant difference (t = −0.607, df = 187, p = 0.544).
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