Deforestation and the population decline of army ants.
During the last century, human land-use has dramatically changed landscapes globally. The effects of natural habitat loss on biodiversity are most severe in tropical rain forests which host the majority of the world’s plant and animal diversity (Whitmore 1998). As many rain forest animal species strongly depend on forest habitat and may not survive in agricultural land, deforestation endangers the survival of animal populations and species on a regional and global level (Millennium Ecosystem Assessment 2005; Loh et al. 2008). While the detrimental effects of deforestation for many forest dependent animals are understood, detailed spatial data of rain forest loss over larger temporal scales and its effect on species are scarce, particularly for insects.
During the last century, human land-use has dramatically changed landscapes globally. The effects of natural habitat loss on biodiversity are most severe in tropical rain forests which host the majority of the world’s plant and animal diversity (Whitmore 1998). As many rain forest animal species strongly depend on forest habitat and may not survive in agricultural land, deforestation endangers the survival of animal populations and species on a regional and global level (Millennium Ecosystem Assessment 2005; Loh et al. 2008). While the detrimental effects of deforestation for many forest dependent animals are understood, detailed spatial data of rain forest loss over larger temporal scales and its effect on species are scarce, particularly for insects.
Data on states and trends in population sizes are important as they allow the threat status of species to be inferred, and are often required to justify conservation programmes. However, these data are scarce for insects, and mostly restricted to a few Lepidoptera species in temperate regions (Thomas et al. 2004; Conrad et al. 2006). To the best of our knowledge, hardly any data are available on trends in population sizes of insect species in tropical rain forests (see Franks 1982, for an exception), mostly because of a lack of historical population count data. Predictive habitat distribution models (PHDMs), relating the occurrence or abundance of a species to environmental predictors, may help to solve this deficiency, as they allow estimations of population sizes across large areas and for historical landscapes. In this study, we developed a PHDM and applied it to forest cover data covering almost 100 years to estimate trends in the population size of the army ant Dorylus (Anomma) wilverthi Emery, a keystone species of Congo-Guinean rain forests, in western Kenya.
Swarm-raiding army ants are prime invertebrate predators in tropical forests. African swarm-raiding army ants, also known as ‘driver ants’, constitute a monophyletic group within the old world army ant genus Dorylus (Kronauer et al. 2007). The ants forage in huge fan-shaped swarms consisting of several hundred thousands to millions of workers, which progress at a speed of roughly 6–12 m h−1 over the forest floor, while the ants search in the leaf-litter and understorey for animal prey (Gotwald 1995; Schöning, Njagi & Franks 2005). Colonies of African swarm-raiding army ants live nomadically, i.e. they frequently emigrate from an old nesting site to a new one (Gotwald 1995), a behaviour which is assumed to be a consequence of food depletion in the surroundings of their nesting sites (Schöning, Njagi & Franks 2005).
Colonies of D. wilverthi appear to strongly depend on forest habitat, as they are rarely found in agricultural land or small forest fragments of < 110 ha (Peters et al. 2009). The species is widely distributed in Central African rain forests but in Kenya it is restricted to the Kakamega Forest. The conservation of D. wilverthi in the area is of high relevance as the Kakamega Forest represents the easternmost part of the distributional range of the species and shows genetic variation unknown in other localities (D.J.C. Kronauer, M.K. Peters, C. Schöning, J.J. Boomsma, unpublished data). Moreover, several Congo-Guinean bird species, also restricted to the Kakamega Forest area within Kenya, depend on this ant species (Peters & Okalo 2009). Consequently, the extinction of D. wilverthi in Kakamega would seriously reduce the distributional range of the ant and may result in a cascade of local species population depletions.
Colonies of D. wilverthi appear to strongly depend on forest habitat, as they are rarely found in agricultural land or small forest fragments of < 110 ha (Peters et al. 2009). The species is widely distributed in Central African rain forests but in Kenya it is restricted to the Kakamega Forest. The conservation of D. wilverthi in the area is of high relevance as the Kakamega Forest represents the easternmost part of the distributional range of the species and shows genetic variation unknown in other localities (D.J.C. Kronauer, M.K. Peters, C. Schöning, J.J. Boomsma, unpublished data). Moreover, several Congo-Guinean bird species, also restricted to the Kakamega Forest area within Kenya, depend on this ant species (Peters & Okalo 2009). Consequently, the extinction of D. wilverthi in Kakamega would seriously reduce the distributional range of the ant and may result in a cascade of local species population depletions.
Changes in total forest cover in the Kakamega Forest area from 1913 to 2003 and its predicted influence on the population size of Dorylus wilverthi. ROS is the ‘Reserve Only Scenario’, in which total forest loss outside of the national/nature reserves was assumed.
Figure is from the article:
Deforestation and the population decline of the army ant Dorylus wilverthi in western Kenya over the last century.
Figure is from the article:
Deforestation and the population decline of the army ant Dorylus wilverthi in western Kenya over the last century.
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