Potential causes of population declines in forest fragments in an Amazonian frog

Forest fragmentation results in population declines and extinctions for many forest vertebrates, but little is known about the mechanisms causing declines in fragments. We investigated potential causes of declines in forest fragments for an Amazonian forest frog (Colostethus stepheni) at an experimental fragmentation study site in central Amazonian Brazil using field estimates of abundance and vital rates coupled with population simulations. Although adult male survival was not reduced by fragmentation, mean clutch size was reduced by 17%. Population simulations demonstrate that a reduction in clutch size of this magnitude is sufficient to cause the observed magnitude of population declines in fragments. Female snout-vent length was also reduced in fragments and may be related to the observed reduction in clutch size. (C) 2003 Elsevier Science Ltd. All rights reserved.