PARENT SESSION
Poster Session 31: Rare, Threatened, and Endangered Species
Thursday, August 11, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Effects of chronic anthropogenic disturbance on the demographic behavior of two species of Mammillaria (Cactaceae).

Ureta , Carolina ^*,1, Martorell, Carlos¹, ¹ Universidad Nacional Autónoma de México, México, D.F., México

ABSTRACT- Several species in the genus Mammillaria are threatened by chronic anthropogenic disturbance. Demographic studies are necessary for their conservation in the presence of human activities. Mammillaria hernandezii and Mammillaria dixanthocentron, which are protected by Mexican laws and endemic to the state of Oaxaca, Mexico, were studied in two sites differing in disturbance intensity. In each site an area was fenced so that a part of the population remained isolated from disturbance factors such as livestock raising and tree felling. The population dynamics was followed for three years, and the population growth rate () was calculated. A demographic retrospective analysis (LTRE) was applied to detect which vital rate contributes the most to the differences between s. In both species it was stasis and growth variations that made the greatest contributions to . The variability of years was the factor affecting the most in both species. In M. hernandezii was higher both outside the fence and in the year 2001, which was the driest one. Furthermore, the site which had the greatest was the site with more disturbance . This suggests that this plant tolerates conditions that other plants cannot, consequently experiencing less competition in driest years and more disturbed sites. However, was larger inside the fence in the disturbed site and outside of it in the less disturbed one. For M. dixanthocentron was larger inside the fence and in the less disturbed site, as expected. The best year for this plant was also 2001, suggesting that it may also suffer negative effects from competition in rainier years. In conclusion M. dixanthocentron prefers to grow in a less disturbed area isolated from human activities. These results agree with the fact that this genus is affected by anthropogenic disturbance due to the traits typical of other Cactaceae. Even though M. hernandezii tolerates more disturbance, but still has a threshold above which disturbance is detrimental.

Key words: conservation, ltre, Mammillaria hernandezii, Mammillaria dixanthocentron