Migrating frogs fare poorly when habitat altered
Migrating frogs fare poorly when habitat altered
mongabay.com
December 19, 2007
Habitat loss and fragmentation are putting amphibians already threatened by climate change, pesticides, alien invasive species, and the outbreak of a deadly fungal infection at greater risk of extinction, reported a study published in Science last week.
A team of Brazilian researchers identified “habitat split” — which they define as “human-induced disconnection between habitats used by different life history stages of a species” — as a key determinant of species richness decline in the Brazilian Atlantic Forest, a critically endangered ecosystem.
Many amphibians lay their eggs in water with offspring emerging as water-dependent larvae (tadpoles for frogs and toads). The young eventually grow into their adult form and move into forest areas. Habitat split occurs when the migration path between forest habitat and aquatic breeding grounds are disrupted by forest clearing or other human activities. Amphibians must then “make risky breeding migrations between suitable aquatic and terrestrial habitats”.
 Brazilian Horned Frog Proceratophrys boiei, a leaf-litter species with aquatic larvae that has been demonstrated to suffer with habitat split. In the background, we can see the wetness of its natural habitat, the Brazilian Atlantic Forest. |
“We found that habitat split negatively affects the richness of species with aquatic larvae but not the richness of species with terrestrial development,” wrote the authors. “This mechanism helps to explain why species with aquatic larvae have the highest incidence of population decline.”
“Adults of species with aquatic larvae, in order to breed, are obliged to abandon forest remnants to reach water bodies, and at the end of the reproductive season, both adults and juveniles are forced to locate and return to forest remnants,” the authors continued. “During this compulsory migration, they face multiple hazards that are associated with environmental conditions within the intervening matrix, such as dehydration, predation, agrochemicals, and other pollutants… In human-altered landscapes, habitat split can be
expected to reduce population sizes, decrease the extent and occupancy rates of metapopulations, and affect negatively the richness of local communities.”
The researchers say the findings help identify what species are potentially at greatest risk of extinction, while reinforcing the need to conserve and restore vegetation along waterways.
CITATION: Becker, C.G. et al (2007). Habitat Split and the Global Decline of Amphibians. Science Dec. 14, 2007
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