La severa transformación antropogénica del paisaje selvático original de Los Tuxtlas y la enorme riqueza biológica de esta región han servido como modelo para describir y entender los efectos del cambio antropogénico sobre la conservación de aves y mamíf

Bat studies: conservation research in southern Mexico

Chiroptera

Laboratorio de Primatología

Estación de Biología Tropical Los Tuxtlas, Instituto de Biología

Universidad Nacional Autonoma de Mexico

Bats are an important group of mammals that share the forest with non volant mammals such as howler and spider monkeys. In spite of differences between these two groups of mammals - nocturnal versus diurnal, volant versus non-volant, indirect interactions occur between these two groups in the forest canopy. These interaction have to do with the ways in which these two groups share food resources in the canopy, specifically fruit. As a result of this, the study of bats species assemblages has been of interest in our ecological and conservation oriented research in the field station Los Tuxtlas of UNAM in southeast Mexico.

In tropical environments bats account for 40-50% of the mammals present in any given habitat/region. Due to the high diversity of feeding habitats (based on nectar feeding and fruit-eating, on hunting insect and vertebrate prey, and on feeding on blood) and their varied and complex flight patterns of flight, bats play an important role in ecological processes in tropical forests. For example, they disperse the seeds of many plant species which are their sources of fruit, favoring their persistence and contributing to the natural process of forest regeneration. Similarly, those bats that depend on animal protein as a source of food, may regulate in important ways insect populations and those of some small vertebrate species.

(photos to the right - cortesy of Bat Conservation Internacional. www.batcon.org )

In the last few decades tropical forests have undergone a rapid process of transformation in its original distribution in the Neotropics. These changes have been the result of human activities such as food production, mining, oil exploration, colonization, and dam building, among others.

It is generally assumed that because of their capacity to fly, bats are little affected by forest fragmentation and hábitat loss. However, recent evidence suggest that bats are sensitive to habitat loss and isolation and that species may also very in their ability to respond to these changes. Unfortunately little information is available in the scientific literature regards the adjustments and strageies bats display to adapt to habitat discontinuity by human activity. Such void of information makes the task of preserving bat populations and species difficult.

Several features of bats make them adequate models for monitoring and studying biodiversity, and for running diagnostic surveys on the impact of forest fragmentation caused by human activity on the persistence of plants and animals in the tropics. These features are:

· The species assemblages are very diverse

· Populations are relatively numerous

· They occupy a highly diverse assemblage of ecological niches and display a high diversity of habits

· They are sensitive to habitat loss, habitat fragmentation and habitat degradation by human activity

· They are relatively easy to sample and study

Tropical forests of Mesoamérica, including those of southern Mexico, have undergone a vast reduction in their original geographic distribution as a result of human activity. Deforestation rates according to FAO statistics are estimated at 400,000 ha/yr.

Three important medium and long-term effects of forest fragmentation upon animal populations are:

Reduction in the effective size of the populations
Isolation of remnant populations
Local extinction of populations and species

An important research task is to document how populatiosn and species respond to changes in habitat availability as a result of human activity, and to design conservation measures to prevent the above three consequences.

The study of the behavioral and demographic responses of bats to habitat loss and fragmentation can tell us much about the plasticity of response of the various species that compose the assemblages in particular regions or localities. A landscape perspective is an adequate approach here, as it allows looking at the opportunities for persistence, or lack of these, bats may have in human modified landscape.

Such perspective can help us generate descriptive and predictive models of changes in the originally forested landscapes, and how bats may, or may not be, adapting to these.

With this information at hand we can attempt to assess alternatives of land management systems that cold promote conservation of bat populations and species, while at the same time improving the local subsystem economies.

Our studies are aimed at sampling bat species assemblages in three landscape scenarios: continuous forest, moderately fragmented forests and highly fragmented forests. These we have been investigating in sites in Los Tuxtlas, in Parque Nacional Palenque and in the Yucatan peninsula.

In the majority of the cases we sample the fragmented landscapes adjacent to the continuous forest, while in others we restrict ourselves to fragmented landscapes - where there is no continuous forest left.

More recently we have become interested in assessing the value of arboreal agroecosystems found in fragmented landscapes for bat conservation. Here we are studying bat species assemblages in cacao, coffee, livefences, allspice, and citrus agroecosystems, among others.

Below we present a general account of the sampling systems we employed to simple bats. We use mist-nets to determine the presence of species and ultrasound detectors to measure the activities of bats in various habitats.

Studies of bats in naturally fragmented landscapes

While forest fragmentation caused by human activity takes place on an ecological scale, natural fragmentation has taken place over geologic time. Hence, bat species existing in these latter landscapes have developed adjustments and adaptations to existing in a fragmented environment, without necessarily becoming extinct. Thus study of bats in naturally fragmented landscapes can help us raise the level of precision of our interpretations about how bats respond to fragmentation of their habitat by human activity.

Fortunately for our interests, in Mexico there is a geographic region in the Yucatán peninsula constituted by naturally formed islands of tropical rain forest vegetation amidst a matrix of natural savannas. These islands of vegetation, termed “petenes” are particularly diverse in their mammal fauna, including bats. Our study in this region began in 2001 in collaboration with Dr. Salvador Montiel, research scientist in the Dept of Human Ecology of CINVESTAV-Mérida research institute, and principal investigator of the bat project in the petenes ecosystem.

For more information regarding this research program, please visit the site below:

http://www.mda.cinvestav.mx/proy_fauna/proyectobats.htm

The study is being conducted in two adjacent reserves, located along the western coast of the Yucatan peninsula: the biosphere reserve of Celestum and the reserve of Los Petenes.

The map to the right shows the location of these reserves and the satellite image shows the boundaries of the Celestum reserve and the distribution of the forest islands (scattered small green areas) or petenes immerse in a “sea” of natural savannas.

For more information on the above research projects and results from these investigation, please access the link “publications” in the main page of this web site or write to <[email protected]>

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