Frogs and a cloud-forest edge in Ecuador

Abstract:

Edge effects on tropical faunas may differ between highland and lowland sites and may therefore require different conservation strategies. In northwestern Ecuador, we examined the frog fauna on both sides of a boundary between wet Andean forest and agricultural lands, asking the following questions: (1) What is the nature of the response of frogs to edge? (2) Does the response change with land use? (3) What conservation measures are suggested by the first two questions? We set up 12 study plots along 16 km of convoluted boundary in one watershed. Each plot contained an agricultural parcel bordering a rectangle extending into the forest. In the dry season of 1996, following local tradition each agricultural parcel was cleared of second-growth vegetation and then burned, planted, cultivated, and (in six cases) harvested 1 year later. Half the parcels were planted in pasture grasses; the others were planted with corn and beans. We randomly assigned each treatment to two sites within each of three blocks. At each site, parallel to the boundary we set up eight all transects, four on the forest side of the boundary and four on the agricultural side. We censused frogs in plots with visual-encounter surveys along all transects in four different seasons from just after planting to just before crop harvest. Regardless of land use or survey date, frog-capture frequencies changed abruptly at the forest-agriculture boundary and then remained constant regardless of distance into the forest or into the cultivated parcels. Forest transects provided 95% of the 2111 captures; all but 5 captures were of Eleutherodactylus spp. (Leptodactylidae). Eleutherodactylus leoni dominated the forest frog fauna but was rare throughout agricultural parcels. The second most common species, E. w-nigrum, displayed the opposite pattern. The stepwise nature of these responses differs from results of studies in tropical lowlands and suggests that edge effects that might penetrate from highland agriculture into cloud forest may be of far less conservation concern than the absolute loss of habitat as the agricultural boundary creeps upslope. This suggestion should be viewed with caution because the scope of our study included only one watershed, two idiosyncratic land-use treatments, and a unique vertebrate taxon.

Año de publicación:

2002

Keywords:

Fuente:

scopus