La modificacion de las comunidades de coleopteros Melolonthidae y Scarabaeidae en dos areas protegidas mexicanas tras dos decadas de estudios faunisticos

A chronological comparative study of the phytophagous and copro-necrophagous scarab beetles (Melolonthidae and Scarabaeidae) was made using data obtained during faunistic studies in two Mexican protected areas. The tropical rain forest in the Tropical Biology Station UNAM "Los Tuxtlas", State of Veracruz, and the oak-pine forest in the Biosphere Reserve "La Michilía", State of Durango, were sampled during two periods (1971-79 and 1984-90) mainly using light and bait traps. At "Los Tuxtlas" an increased number of species was recorded, 60 to 109 in the Melolonthidae, and 31 to 45 in the Scarabaeidae. At "La Michilía" a decreased number of species of Melolonthidae (39 to 33) and an increment in the number of Scarabaeidae (17 to 29 species) were recorded. The statistical analysis of the data supports a good sample effort during the four periods in both areas, since we obtained the 78-100 per cent of the expected number of species. Wide variations in the diversity and equity indexes suggest that some important changes took place in both environments, especially due to the human activities in the non-protected surrounding areas. The noteworthy differences are analysed and commented. The present isolation of the tropical rain forest patch of the "Los Tuxtlas" station, amidst secondary vegetation and cattle lands, probably explains the recent scarab beetle richness. The changes in the Melolonthidae diversity at "La Michilía" are not easy to explain.