IMBIV   05474
INSTITUTO MULTIDISCIPLINARIO DE BIOLOGIA VEGETAL
Unidad Ejecutora - UE
capítulos de libros
Título:
Human impacts on pollination, reproduction and breeding systems in tropical dry forest plants
Autor/es:
QUESADA, M.; ROSAS, F.; AGUILAR, R.; ASHWORTH, L.; ROSAS-GUERRERO, V.; SAYAGO, R.; LOBO, J.A.; HERRERÍAS- DIEGO, Y.; SANCHEZ-MONTOY, G
Libro:
Seasonally Dry Tropical Forests: Ecology and Conservartion
Editorial:
Island Press
Referencias:
Lugar: Washington; Año: 2011; p. 173 - 194
Resumen:
Over the last two decades several studies have shown that plant species of contrasting life-forms ranging from small herbs to large trees may experi-ence a decline in reproductive success following habitat fragmentation and population disruption (Bawa 1990; aizen and Feinsinger 1994; aguilar et al. 2006). Such outcome has been shown for many plants throughout the tropics, particularly trees, where human activities have resulted in elevated rates  of  habitat  fragmentation  and  degradation  (Ghazoul  and  Shaanker 2004; Quesada and Stoner 2004; Quesada et al. 2004). Because almost 90 percent of angiosperms (i.e., flowering plants) depend on animals for effec-tive pollination and sexual reproduction (Buchmann and Nabhan 1996), it is of central concern to understand the capacity of pollinators for transfer-ring pollen among individuals and its consequences on plant reproduction in newly created anthropogenic landscapes.While  evolutionary  dependence  of  plants  on  animal  mutualists  for sexual  reproduction  has  improved  pollen  transfer  to  stigmas,  it  has  also prompted increased plant susceptibility to fragmentation and other forms of anthropogenic disturbance that characterize today?s landscapes (e.g., ai-zen et al. 2002; ashworth et al. 2004). Changes in abundance, composi-tion, and/or foraging behavior of pollinators as a consequence of habitat disturbance will have an effect on the amount and/or quality (autogamous 174   seasonally dry tropical forestvs. xenogamous) of pollen deposited on stigmas, thus affecting reproduc-tion and the genetic structure of plants (Wilcock and Neiland 2002). Much research has been conducted with regard to the effects of habitat loss and fragmentation on pollination, plant reproduction, and genetic di-versity of plant populations over the past 20 years. Nevertheless, there has been certain research bias in the selected natural systems evaluated, where species from tropical forests represent only 16 percent of the entire studied species around the world (aguilar et al. 2006, 2008). Moreover, no specific analysis of this subset of species has yet been conducted. this comparative underrepresentation of tropical plant species in fragmentation studies high-lights the need to focus more thoroughly on population studies from these threatened and fragile habitats.Some expected outcomes of habitat fragmentation include local extinc-tion of plant and animal populations, the alteration of species richness and abundance,  and  changes  in  the  trophic  structure  of  communities. these negative effects of habitat fragmentation can be expressed at the landscape and population levels. at the landscape scale, fragmentation involves the transformation of a large area of habitat into several patches of smaller size, isolated from each other by surrounding anthropogenic habitats different from the original. Such loss and breaking apart of the habitat alters nega-tively the connectivity, functioning, and biodiversity within the matrix of the fragmented habitat (Fahrig 2003). at the population level, habitat frag-mentation may reduce the effective population size and the magnitude and direction of gene flow, which in turn would produce negative changes in the population and genetic structure of plant species (Young et al. 1996; aguilar et al. 2008). the reduction of both gene flow and effective popula-tion size by habitat fragmentation may cause inbreeding, genetic drift, and a  consequent  decline  of  genetic  variation.  therefore,  the  loss  of  genetic diversity may limit the ability of local populations to respond selectively to varying local conditions, compromising their persistence and increasing their risk of extinction due to inbreeding depression.Habitat fragmentation may not only lead to a reduction in population size  and  genetic  variation  but  also  disrupt  key  interactions  of  the  plants with their pollinators and seed dispersers. the interaction between plants and  pollinators  can  be  disrupted  by  habitat  loss,  reduction  of  pollinator abundance, changes in floral resource availability and distribution, or com-petitive exclusion from floral resources by inefficient or exotic pollinators. Most of the plant-pollinator interactions may depend on the relative abun-dance of floral resources, thus changes in plant abundances caused by forest disturbance may lead to modification in the composition, functioning, and Human Impacts on Pollination, reproduction, and Breeding Systems   175maintenance of plant-pollinator webs (aizen and Feinsinger 2003; Lope-zaraiza et al. 2007). We should expect small isolated or fragmented plant populations to be less attractive to pollinators than large populations. as a result of this, rates of pollinator visitation and seed production may often be lower in small than in large populations of plants pollinated by animals. the negative consequences of habitat fragmentation for plant popula-tions could be exacerbated by the complex interactions of reproductive (sex expression) and mating systems (selfing vs. outcrossing or mixed strategies) in combination with population size and pollination and seed dispersal sys-tems. Previous studies of seasonally dry tropical forests (SDtFs) indicate that  the  reproduction  of  plants  is  dependent  on  the  presence  of  natural pollinators (Frankie et al. 1974; Bullock 1985). therefore, changes in the abundance and activity patterns of pollinators induced by habitat fragmen-tation are expected to reduce gene flow between isolated plant populations. the negative effects of forest fragmentation on the viability of populations could be particularly noticeable in tropical tree species that posses self-in-compatibility systems and depend on pollinators for sexual reproduction (Bawa 1974, 1990; aguilar et al. 2006). Disturbances that impact animal vectors of pollen transfer may therefore affect the reproductive output of tropical trees. Pollination of tropical plants is mainly conducted by animal vectors such as bees, butterflies, flies, birds, and bats, and the natural popu-lations of these animals inhabit and depend on the existence of forests.the objectives of this chapter are to (1) evaluate the effects of forest fragmentation on plant-pollinator interactions, plant phenology, reproduc-tive dynamics, and genetic parameters of tropical plants; (2) describe and compare plant life-history traits, pollination systems, and plant reproduc-tive traits between tropical forests; and (3) predict vulnerability patterns to forest fragmentation based on ecological and reproductive traits of plants.