Distribution,abundance, and habitat use of introduced <Emphasis Type="Italic">Boa constrictor</Emphasis> threatening the native biota of Cozumel Island,Mexico

Species introductions are among the most pervasive types of disturbance, seriously affecting island biota and ecosystem dynamics. The management of introduced generalist species, which may live in a wide range of environmental conditions, can be particularly difficult and is a major challenge for the conservation of native insular species. Boa constrictor was introduced onto Cozumel Island, Mexico, in 1971. The introduction of this generalist predator has affected negatively the native species (many of them endemic to the island) on which the boa feed. It is important to determine temporal variation in boa abundance, the areas of the island in which boas live, and the vegetation types they use in order to develop management strategies to reduce boa pressure on the native biota. We used nocturnal road transect sampling and occasional boa encounters during field work, to estimate boa distribution, abundance and habitat use, taking into account its spatiotemporal patterns on Cozumel Island. This study confirms that Boa constrictor is well established, widespread, and abundant on the island. Our results show that boas are distributed throughout Cozumel, in all vegetation types and geographical regions. Overall, there were 0.11 ± 0.03 boa/10 km road transect. There were no significant spatiotemporal differences in boa activity (time of day) and abundance (monthly, seasonally, by vegetation types or regions of the island). According to the habitat use analysis, there were, however, fewer boas than expected in the subdeciduous tropical forest we sampled and in the central-northern region of the island, which coincide with areas inhabited by humans. There were more boas in areas uninhabited by humans, and there was a tendency towards a greater proportion of dead boas in inhabited areas and live boas in uninhabited areas. Cozumel boas are habitat generalists, which are affected by human induced mortality in inhabited areas. There is a vast area uninhabited by humans, with natural vegetation, on the island where boas have suitable habitats available for their continuous existence on Cozumel. This situation, and the adaptability of the boa, makes the control or eradication of this introduced species a critical conservation challenge.     

The status of dwarf carnivores on Cozumel Island, Mexico

Cozumel Island in the Mexican Caribbean is inhabited by four carnivores, of which two, the Cozumel coati Nasua nelsoni and pygmy raccoon Procyon pygmaeus, are endemic species. The taxonomic status of a third carnivore, a dwarf gray fox Urocyon cinereoargenteus, is undetermined, but may deserve subspecific or species-level recognition. The fourth species, the kinkajou (Potos flavus), may be a recent introduction. We review the status of these carnivores, report our field observations and results of line transect and trapping efforts, discuss current threats to these taxa, and make recommendations for their conservation. A population density of 0.43 ± 0.27 coatis/km², and a total island population size of 150 ± 95 individuals, was estimated from 386 km of line transects in 1994–1995. Intensive trapping efforts (1479 trap-nights) in 2001 at multiple localities were unsuccessful. Pygmy raccoons were observed in the mangrove and coastal wetland areas of the island and in 2001 we captured 11 individuals with the same sampling efforts as for coatis (8.8 raccoons/1000 trap-nights). The gray fox is also apparently very rare on the island. While a few observations of the animals have been made (1984, 1994 and 2001), no animals were seen along transects and none were trapped. The primary threats to the persistence of these taxa include introduced congeners, introduced predators, parasite and disease spill-over from exotic animals, habitat fragmentation, hunting and collection as pets, and hurricanes. We suggest that the Cozumel coati, pygmy raccoon, and the Cozumel population of the gray fox be considered as Critically Endangered according to the IUCN classification system. Current conservation actions focusing on Cozumel carnivores are extremely limited. We recommend eradication of introduced species, maintenance of habitat connectivity, ex situ conservation programs, explicit public policies on land-use and sustainable development, public awareness campaigns, and continuous scientific research and monitoring.     

Effects of exotic mongoose (Herpestes javanicus) on the native fauna of Amami-Oshima Island, southern Japan, estimated by distribution patterns along the historical gradient of mongoose invasion

We examined the distribution patterns of native animals on Amami-Oshima Island, southern Japan, along a historical gradient of mongoose establishment and estimated the effects of mongoose on the native fauna. To assess the relative abundance of various ground-dwelling animals, we used the following four methods; sensor cameras for exotic mammals, nighttime driving census for nocturnal native vertebrates, line census for ground-dwelling lizards, and adhesive traps for arthropods. The results indicated that seven species with larger body size, including mammals, birds, reptiles, and amphibians, were rarely observed in mongoose-infested area. By contrast, medium-sized animals showed neutral relationships with mongoose establishment. Interestingly, the densities of smaller-sized animals were higher in mongoose-infested area. It could be interpreted that smaller species have increased in abundance through top-down cascades, i.e., decreases in native predators such as frogs and lizards caused by the mongoose have resulted in increases in the abundance of smaller animals. Predation pressures by mongoose and native predators may be canceled out for medium-sized animals, causing neutral responses to mongoose by these animals. This study appears to be the first example that shows the influence of mongoose on a wide variety of native animals. In addition, our findings indicate the importance of considering the food web structure of a recipient ecosystem and contribute to the prediction and assessment of ecological risks caused not only by mongoose, but also by other invasive top predators.