title: Anthropogenic disturbances jeopardize biodiversity conservation within tropical rainforest reserves.
abstract: Anthropogenic disturbances affecting tropical forest reserves have been documented, but their ecological long-term cumulative effects are poorly understood. Habitat fragmentation and defaunation are two major anthropogenic threats to the integrity of tropical reserves. Based on a long-term (four decades) study, we document how these disturbances synergistically disrupt ecological processes and imperil biodiversity conservation and ecosystem functioning at Los Tuxtlas, the northernmost tropical rainforest reserve in the Americas. Deforestation around this reserve has reduced the reserve to a medium-sized fragment (640 ha), leading to an increased frequency of canopy-gap formation. In addition, hunting and habitat loss have caused the decline or local extinction of medium and large herbivores. Combining empirical, experimental, and modeling approaches, we support the hypothesis that such disturbances produced a demographic explosion of the long-lived (≈120 y old, maximum height of 7 m) understory palm Astrocaryum mexicanum, whose population has increased from 1,243-4,058 adult individuals per hectare in only 39 y (annual growth rate of ca 3%). Faster gap formation increased understory light availability, enhancing seed production and the growth of immature palms, whereas release from mammalian herbivory and trampling increased survival of seedlings and juveniles. In turn, the palm's demographic explosion was followed by a reduction of tree species diversity, changing forest composition, altering the relative contribution of trees to forest biomass, and disrupting litterfall dynamics. We highlight how indirect anthropogenic disturbances (e.g., palm proliferation) on otherwise protected areas threaten tropical conservation, a phenomenon that is currently eroding the planet's richest repositories of biodiversity.
authors.affiliation: Laboratorio de Ecología y Manejo de Bosques Tropicales, Instituto de Investigaciones en Ecosistemas y Sustentabilidad, Universidad Nacional Autónoma de México, Morelia, Michoacan 58190, Mexico;
authors.forename: Miguel
authors.initials: M
authors.lastname: Martínez-Ramos
authors.affiliation: Laboratorio de Ecología y Manejo de Bosques Tropicales, Instituto de Investigaciones en Ecosistemas y Sustentabilidad, Universidad Nacional Autónoma de México, Morelia, Michoacan 58190, Mexico;
authors.forename: Iván A
authors.initials: IA
authors.lastname: Ortiz-Rodríguez
authors.affiliation: Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, Cd. de Mexico 04510, Mexico;
authors.forename: Daniel
authors.initials: D
authors.lastname: Piñero
authors.affiliation: Department of Biology, Stanford University, Stanford, CA 94305;
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Dirzo
authors.affiliation: Departamento de Ecología de la Biodiversidad, Instituto de Ecología, Universidad Nacional Autónoma de México, Cd. de Mexico 04510, Mexico; El Colegio Nacional, Cd. de Mexico CP 10740, Mexico sarukhan@unam.mx.
authors.forename: José
authors.initials: J
authors.lastname: Sarukhán
mesh_terms: D000818:Animals; D044822:Biodiversity; D003247:Conservation of Natural Resources; D017753:Ecosystem; D006801:Humans; D065947:Rainforest; D014197:Trees; D014329:Tropical Climate
keywords: cascading effects; conservation; defaunation; fragmentation; plant demography