Abstract
AbstractAimCurrent species distributions are shaped by present and past biotic and abiotic factors. Here, we assessed whether abiotic factors (habitat availability) in combination with past connectivity and a biotic factor (body mass) can explain the unique distribution pattern of Southeast Asian mammals, which are separated by the enigmatic biogeographic transition zone, the Isthmus of Kra (IoK), for which no strong geophysical barrier exists.LocationSoutheast Asia.TaxonMammals.MethodsWe projected habitat suitability for 125 mammal species using climate data for the present period and for two historic periods: mid‐Holocene (6 ka) and last glacial maximum (LGM 21 ka). Next, we employed a phylogenetic linear model to assess how present species distributions were affected by the suitability of areas in these different periods, habitat connectivity during LGM and species body mass.ResultsOur results show that cooler climate during LGM provided suitable habitat south of IoK for species presently distributed north of IoK (in mainland Indochina). However, the potentially suitable habitat for these Indochinese species did not stretch very far southwards onto the exposed Sunda Shelf. Instead, we found that the emerged landmasses connecting Borneo and Sumatra provided suitable habitat for forest dependent Sundaic species. We show that for species whose current distribution ranges are mainly located in Indochina, the area of the distribution range that is located south of IoK is explained by the suitability of habitat in the past and present in combination with the species body mass.Main conclusionsWe demonstrate that a strong geophysical barrier may not be necessary for maintaining a biogeographic transition zone for mammals, but that instead a combination of abiotic and biotic factors may suffice.
Highlights
It is widely accepted that species distributions and biodiver‐ sity patterns result from the interplay of both biotic and abiotic factors (Soberón, 2007), those currently active, and those experienced in the past (Dullinger et al, 2012; Svenning, Eiserhardt, Normand, Ordonez, & Sandel, 2015; Svenning & Skov, 2007a)
We assessed whether abiotic factors in combina‐ tion with past connectivity and a biotic factor can explain the unique distribution pattern of Southeast Asian mammals, which are separated by the en‐ igmatic biogeographic transition zone, the Isthmus of Kra (IoK), for which no strong geophysical barrier exists
The area of the habitat that is currently located south of IoK for Indochinese species was affected by the abiotic factor and the biotic factor, but we found no significant effect of connectivity (F = 0.03, d.f. = 1, p = .86)
Summary
It is widely accepted that species distributions and biodiver‐ sity patterns result from the interplay of both biotic and abiotic factors (Soberón, 2007), those currently active, and those experienced in the past (Dullinger et al, 2012; Svenning, Eiserhardt, Normand, Ordonez, & Sandel, 2015; Svenning & Skov, 2007a). Low sea levels during glacial periods in the last 2 Myr uncovered land bridges that connected Sundaic and Indochinese landmasses (Lohman et al, 2011) Such land bridges could allow for species movement across IoK only if they were covered by suitable habitat. 21 ka and mid‐ Holocene, 6 ka) and present, (b) connectivity of available habitats during the LGM, and (c) biotic factors Based on their present dis‐ tributions, we classified 125 mammal species into two large distri‐ bution groups (Indochina and Sundaland), each with two subgroups, distinguishing the more specialized species (specialized Indochinese: ranges exclusively north of 12° N; specialized Sundaic species: ranges exclusively south of 5° N) from the ones with more general require‐ ments (general Indochinese: ranges predominantly in Indochina, but reaching into the transition zone from 5 to 12° N; general Sundaic: ranges mainly in Sundaland, but protruding into the transition zone). We derived two predictions based on H1: P1 (regarding the total habitat area in the past)—We predict that for general Indochinese species the total area of potentially suitable habitat was higher during the LGM
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