Assessing assemblage-wide mammal responses to different types of habitat modification in Amazonian forests

Abstract

Tropical forests are being heavily modified by varying intensities of land use ranging from structural degradation to complete conversion. While ecological responses of vertebrate assemblages to habitat modification are variable, such understanding is critical to appropriate conservation planning of anthropogenic landscapes. We assessed the responses of medium/large-bodied mammal assemblages to the ecological impacts of reduced impact logging, secondary regrowth, and eucalyptus and oil palm plantations in Eastern Brazilian Amazonia. We used within-landscape paired baseline-treatment comparisons to examine the impact of different types of habitat modification in relation to adjacent primary forest. We examined assemblage-wide metrics including the total number of species, number of primary forest species retained in modified habitats, abundance, species composition, and community integrity. We ranked all types of habitat modification along a gradient of assemblage-wide impact intensity, with oil palm and eucalyptus plantations exerting the greatest impact, followed by secondary regrowth, and selectively logging. Selectively-logged and secondary forests did not experience discernible biodiversity loss, except for the total number of primary forest species retained. Secondary forests further experienced pronounced species turnover, with loss of community integrity. Considering the biodiversity retention capacity of anthropogenic habitats, this study reinforces the landscape-scale importance of setting aside large preserved areas.

Figure 1

Geographic location of each of the four landscapes where medium to large-bodied mammal assemblages were surveyed in Eastern Brazilian Amazonia. Within each landscape, sampling sites are represented by dots and colour-coded according to habitat type: (a) secondary forest (green), (c) eucalyptus plantation (yellow), (d) oil palm plantation (orange) and adjacent primary forest (grey). As an exception, sampling points in the logged forest landscape (b) are half grey-half blue coloured to represent sampling both before and after logging, respectively. Each landscape is amplified to improve clarity in the positional context of sampling sites. In the satellite images (Accessible in https://mapbiomas.org), dark green represents forest areas, with the exception of landscape c, where the Amazon Savannah is predominantly in light green.

Figure 2

Mammal assemblage-wide metrics for human-modified and adjacent primary forest within each landscape: (a–d) rarefied total species richness in modified habitat and the adjacent primary forest, and rarefied number of primary forest species retained in modified habitat; (e–h) species abundance (number of records per 10 km walked); (i–m) species composition, represented in an ordination diagram obtained using the first two NMDS axes; and (n–q) community integrity, defined as the degree of similarity between disturbed and undisturbed habitats. Within each landscape, sampling sites are represented by dots and colour-coded according to habitat type: logged forest (blue), secondary forest (green), eucalyptus plantation (yellow), oil palm plantation (red) and adjacent primary forest (grey). As an exception, dots/triangles in (a–d) represent the rarefied number of species within each habitat type per landscape, which was obtained by further considering the number of records and corresponding sample coverage (see details in the Data Analysis).

Figure 3

Percentage changes (mean ± 95% CIs) in assemblage-wide metrics within anthropogenic habitats compared to their adjacent primary forest baselines: (a) rarefied species richness, (b) rarefied number of primary forest species, (c) overall abundance, and (d) community integrity. Triangles indicate metrics when only primary forest species were included and are colour-coded according to habitat type: primary forest (grey), logged forest (blue), secondary forest (green), eucalyptus plantation (yellow) and oil palm plantation (red).

Figure 4

Species recorded at each sampling site across all four human-modified forest landscapes. At each sampling site (transect), species incidence is denoted by a square that is colour-coded according to habitat type (see legend). Line-transects are ordered left to right within habitat type from most to least species rich.