The coastal Atlantic Forest is one of the most diverse, and most threatened, natural environments in the world [1].
Due to severe human impact over the last few centuries most of the
primary coastal Atlantic Forest has been destroyed. Only 7% of its
original extent remains [1]
and a considerable part of remaining forest takes the form of secondary
forest fragments at different stages of regeneration, embedded in a
rural or urban matrix [2,3].
In fragmented landscapes such as these, both the stage of regeneration
and the degree of fragmentation influence forest structure within the
fragments, which in turn determines habitat suitability and affects
species occurrence as well as the composition of animal communities [4,5]. Since secondary forests may play an important role in species conservation if primary forest habitats are limited [5], it is important to understand which factors determine species distribution in secondary forests.
Although small mammals play a key role in neotropical forest
ecosystems, including the Atlantic Forest, in terms of seed dispersal [6-11], dispersal of mycorrhizal fungi [12] and predation on seedlings [7,10,13,14],
only a limited number of studies focused on the influence of vegetation
structure on small mammal distribution in secondary Atlantic Forest
fragments [15-17].
The effects of forest fragmentation on Atlantic Forest small mammals
vary among species. Some species are able to persist in isolated
fragments and cross or occupy non-native vegetation in human-altered
areas, while others are restricted to large and/or connected forest
remnants [16,18-22]. Since vulnerability to fragmentation is influenced by the capacity to occupy the altered habitats of the matrix [19,21,23-25],
it is expected that preferences on a microhabitat scale in forested
habitats will vary among species showing different degrees of
vulnerability to forest fragmentation on a larger scale.
The identification of the scale that best explains variation in presence or abundance of organisms is a major goal in ecology [26].
This implies the necessity of examining ecological patterns on
different scales. The issue of the "correct" scale at which assessment
of biological parameters should be carried out has been the topic of
numerous studies in ecology [27-32]. In fact, in his review Jorgensen [32]
called attention to the lack of consistent use of the appropriate scale
in small mammal microhabitat research and that broad but widely
accepted generalizations (e.g. habitat partitioning, relation between
abundance and availability of microhabitat) might be based on results
that often confound micro- and macro-habitat effects.
In a recent study on small mammals in Caucaia do Alto, São Paulo, Pardini et al. [16]
showed that three rodent and two marsupial species were affected in
different ways by fragmentation on a macro-scale. The rodents Akodon montensis Thomas, 1902, and Oligoryzomys nigripes (Olfers, 1818) as well as the marsupial Gracilinanus microtarsus (Wagner, 1842) were not affected by fragmentation while the rodent Delomys sublineatus (Thomas, 1903) and the marsupial Marmosops incanus (Lund, 1840) decreased in abundance in smaller and/or more isolated fragments. In the same region, Umetsu & Pardini [21]
showed that the three species not affected by fragmentation were able
to occupy anthropogenic habitats while the species vulnerable to
fragmentation were restricted to native vegetation on a macro-habitat
scale [16,21].
In the present study we extended the previous work by adding a
smaller scale to the investigation of small mammal habitat preferences
in the same Atlantic Forest study area. While Umetsu and Pardini [21]
studied the response of Atlantic Forest small mammal populations to
habitat variation, this study deals with the response of small mammal
individuals to micro-habitat differences. Specifically, we investigated
the influence of vegetation structure on the micro-scale distribution
of three small mammal species not affected by fragmentation (Akodon montensis, Oligoryzomys nigripes, Gracilinanus microtarsus) and two species vulnerable to fragmentation (Delomys sublineatus, Marmosops incanus)
in six secondary forest remnants in the Atlantic Forest fragmented
landscape of Caucaia do Alto. We investigated if the occurrence of
small mammal species is influenced by vegetation structure, aiming to
ascertain whether species with different degrees of vulnerability to
forest fragmentation are associated with distinct vegetation
characteristics.
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