Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → États-Unis → 1982 → SEED PREDATION BY DESERT HARVESTER ANTS AND RODENTS IN CENTRAL MEXICO

University of Pennsylvania (1982)

SEED PREDATION BY DESERT HARVESTER ANTS AND RODENTS IN CENTRAL MEXICO

GONZALEZ-ESPINOSA, MARIO

Titre : SEED PREDATION BY DESERT HARVESTER ANTS AND RODENTS IN CENTRAL MEXICO

Auteur : GONZALEZ-ESPINOSA, MARIO

Université de soutenance : University of Pennsylvania

Grade : Doctor of Philosophy (PhD) 1982

Résumé
The removal of non-native seeds, and pulp, peel, and seeds of Opuntia by rodents, birds, and Pogonomyrmex ants was studied in two semiarid habitats in central Mexico. Scarce and overabundant seed resource conditions were simulated by manipulating the number of Opuntia fruits in 0.64 ha replicated experimental plots. Non-significant differences among treatments were found for the removal of non-native seeds by birds only, and by rodents, birds, and ants together. The birds usually removed less than 20%. The combined seed predation by all granivores was generally higher than 75%. Rodents and ants showed similar levels of seed predation only during late spring and summer. Seed removal from November through March was mostly effected by rodents. The removal of non-native seeds only by rodents was generally not affected by the treatments. Colonies of Pogonomyrmex spp. exposed to scarcity of seeds showed significantly higher removal rates than those under control or overabundance conditions in several of the months when natural seed abundance was lowest. This was effected through more frequent or more intense recruitment of workers on seed clumps. Both Pogonomyrmex ants and rodents showed lower seed removal during 1981, the year of higher natural seed abundance. The results suggest that substantial seed predation escape from rodents and harvester ants may only occur when seeds are very abundant. The coexistence of desert rodents and harvester ants appears to result from their different daily and seasonal foraging schedules. These groups of granivores also show different predator functional responses to varied densities of Opuntia fruits. In both cases a Holling’s type III response was partially suggested by the data. However, the amount of seed and fruit removed by Pogonomyrmex always increased with increasing densities of fruit. The rodents’ response had a maximum at about 400 kg of Opuntia fresh fruit/ha/month, and an eventual decline at the highest fruit densities included in the analyses. Three coexisting species of rodents showed contrasting differences in population densities, migration patterns, extent of area of activity, and other attributes, as a result of the experimental treatments. Their differential responses contribute to the long-term coexistence of the rodent guild in a fluctuating natural system.

Accès au document : Proquest Dissertations & Theses

Page publiée le 7 avril 2015, mise à jour le 14 décembre 2018