Identifying factors that may be responsible for regulating the size of animal populations is a cornerstone in understanding population ecology. The main factors that are thought to influence population size are either resources (bottom-up), or predation (top-down), or interspecific competition (parallel). However, there are highly variable and often contradictory results regarding their relative strengths and influence. These varied results are often interpreted as indicating "shifting control" among the three main factors, or a complex, nonlinear relationship among environmental variables, resource availability, predation, and competition. We argue here that there is a "missing link" in our understanding of predator-prey dynamics. We explore whether the landscape-of-fear model can help us clarify the inconsistencies and increase our understanding of the roles, extent, and possible interactions of top-down, bottom-up, and parallel factors on prey population abundance. We propose two main predictions derived from the landscape-of-fear model: (1) for a single species, we suggest that as the makeup of the landscape of fear changes from relatively safe to relatively risky, bottom-up impacts switch from strong to weak as top-down impacts go from weak to strong; (2) for two or more species, interspecific competitive interactions produce various combinations of bottom-up, top-down, and parallel impacts depending on the dominant competing species and whether the landscapes of fear are shared or distinctive among competing species. We contend that these predictions could successfully explain many of the complex and contradictory results of current research. We test some of these predictions based on long-term data for small mammals from the Chihuahuan Desert in the United States, and Mexico. We conclude that the landscape-of-fear model does provide reasonable explanations for many of the reported studies and should be tested further to better understand the effects of bottom-up, top-down, and parallel factors on population dynamics.

The diversity and organization of the mammalian community is related to the vegetation structure of the coffee plantations in the area of Barranca Grande, in the State of Veracruz, Mexico. Four transects (each 200 m in length) were used to study the vegetation structure within the coffee plantation, and 178 night/traps, tracks registration and information from local people, were used in order to become familiar with the mammalian community. The sample period was from October 1989 to February 1991. The 24 mammals of medium-size species present in the area were classified using two measures of ecological diversity, locomotion and foraging in order to understand the guild organization. If the complexity of the plantation is reduced, the number of guilds occupied could suffer a loss of 45% and 43% in ecological richness and diversity, respectively, and 24% in the equitability of the mammalian fauna. We recommend the maintenance of a high diversity in the tree stratum (shade species), in this case, species such as Inga jinicuil, banana (Musa sapientum), Citrus spp., coyo avocado (Persea schiedeana), mango (Mangifera indica); species which could provide food resources and protection for the mammals.Resumen. En el ~irea de Barranca Grande, Estado de Veracruz, M6xico, se estudi6 la relaci6n que tiene la estructura de la vegetaci6n de los cultivos de caf6 con la diversidad de la comunidad de mamiferos medianos. Para ello, se establecieron 4 transectos fijos de 200 m de largo cada uno, en los que se tomaron los datos de los diferentes estratos. Para conocer la fauna de mamiferos, se hizo un muestreo con trampas Tomahawk (178 noches/trampas), registro de rastros asi como encuestas a la gente que vive en la zona, entre Octubre de 1989 y Febrero de 1991. Se registraron 24 especies de mamiferos medianos que fueron clasificados utilizando dos medidas de diversidad ecol6gica, locomoci6n y forrajeo, para conocer la organizaci6n en gremios. Si se reduce la complejidad de los cafetales, puede existir una reducci6n hasta del 45% en el n~mero de gremios ocupados, 43% en la riqueza y en la diversidad ecol6gica, y 24% en la equitatividad. Se recomienda mantener una alta diversidad en el estrato arb6reo, en este caso especies como el jinicuil (lnga finicuil), plfitanos (Musa sapientum), citricos (Citrus spp.), pagua o aguacate (Persea schiedeana), mango (Mangifera indica), serian recomendables ya que proporcionan recursos alimenticios y protecci6n a la mayoria de los mamiferos.

Aim Coyote (Canis latrans) distribution in Mexico and Central America has expanded recently reaching the Yucatan peninsula, Belize and Panama, probably promoted by deforestation of tropical areas. Historically, the southern distribution of coyotes prior to European settlement in America was described as reaching only as far south as central Mexico and that introduction of livestock favoured migration of coyotes to southern Mexico and Central America. However, coyote fossil records in Central America and Yucatan, as well as observational records of travellers during the sixteenth century suggest that the coyote's arrival to the region was earlier. Because of the uncertainty of past coyote distribution and the possible economic and ecological impacts due to recent range expansion, the objectives of this study were to confirm if paleontological and historical evidence support the hypothesis that the southernmost limit of coyote distribution before the arrival of European settlers was the centre of Mexico, to discuss the possible factors that have influenced historical shifts in coyote distribution, and to model the present distribution of the coyote in Mexico and Central America, determining the areas where they could invade in the near future.

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