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Herpetofauna Abundance and Diversity:

An Indicator for Land Management Disturbance?

Peter Ritson, NW Academy, Portland, OR

David Wojnowski, North Carolina Department of Environment and Natural Resources/Division of Water Resources

Abstract

The rate of capture of herpetofauna in edge and interior forest showed no difference indicating that this survey technique is insensitive to edge effects.

Introduction

Herpetofauna has been widely utilized as a sensitive indicator of environmental disturbance. Research has also shown that global declining amphibian populations have application towards Temperature and moisture effects herpetofauna assemblages. Land management practices, such as clearing of land for pasture, affects ecosystems (amount of sunlight and other abiotic factors). Since reptiles thermoregulate sunny areas may be important to heat their body temperature to a level at which they can move quickly enough to capture and digest prey. On the other hand most amphibians will quickly desiccate in direct sunlight and usually avoid areas with direct sunlight unless sitting in standing water. Our team looked at the edge effect on herpetofauna abundance and diversity in a tropical premontane primary forest adjacent to an agricultural site at Las Cruces, Costa Rica.

Method

2 people walking parallel 100m transects within 2 meters of each other conducted surveys on a single day. One transect was 100 m within the forest interior and the other transect was within 10 m of the disturbed edge. Every 10 meters each person searched 1 square meter of leaf litter. Attempts were made to capture all animals. Only animals positive identified were counted. Capture data was computed as a rate by adding total number of animals caught divided by man hours used.

Results

No herpetofauna was encountered under the leaf litter during the surveys. Two genera, Norops and Eleutherodactylus, were found during surveys (figure #1) Total number of Norops and Eleutherodactylus counted in the interior over 98 man/minutes were 2 and 11 respectively. Total number of Norops and Eleutherodactylus counted on the edge over 90 man/minutes were 2 and 10 respectively. This yielded a capture rate of 1.2 and 1.3 for Norops per man-hour in the interior and edge receptively. This also yielded a capture rate of 6.7 and 6.7 for Eleutherodactylus per man-hour in the interior and edge receptively.

Conclusions

It appears from this visual encounter survey that most herpetofauna in this site are rare, in an unobservable site (canopy, underground) or highly cryptic. The two species found on other hand were tolerant of a wide variety of environmental conditions. They were previously captured in the nearby pasture, which consisted of widely scattered small trees and grass less than 0.5 tall. These capture sites demonstrated that the two species could tolerate extreme conditions. Thus it appears that short-term herpetofauna surveys do not document changes in environmental conditions caused by edge effects.

Figure 1: Herpetofauna abundance and diversity on the edge and interior of forest. The figure shows the rate of capture of the two genera per person search hour. No difference was detected between edge and interior. "n" is the total number of animals caught during the study period.