Abstract
We aimed to determine the conservation status of medium- and large-sized mammals and evaluate the impact of 500 years of forest fragmentation on this group of animals in the Pernambuco Endemism Center, in the biogeographical zone of the Atlantic forest north of the São Francisco River in northeastern Brazil. Line transect surveys were performed in 21 forest fragments, resulting in a checklist of the mammals of the entire Pernambuco Endemism Center area. We ran a generalized linear model (Factorial ANCOVA) to analyze to what extent the vegetation type, fragment area, isolation, sampling effort (as total kilometers walked), or higher-order interactions predicted (a) richness and (b) sighting rates. To determine if the distribution of the species within the forest fragments exhibited a nested pattern, we used the NODF metric. Subsequently, we performed a Binomial Logistic Regression to predict the probability of encountering each species according to fragment size. Out of 38 medium- and large-sized mammal species formerly occurring in the study area, only 53.8% (n = 21) were sighted. No fragment hosted the entire remaining mammal community, and only four species (19%) occurred in very small fragments (73.3% of the remaining forest fragments, with a mean size of 2.8 ha). The mammalian community was highly simplified, with all large mammals being regionally extinct. Neither the species richness nor sighting rate was controlled by the vegetation type, the area of the forest fragments, isolation or any higher-order interaction. Although a highly significant nested subset pattern was detected, it was not related to the ranking of the area of forest fragments or isolation. The probability of the occurrence of a mammal species in a given forest patch varied unpredictably, and the probability of detecting larger species was even observed to decrease with increasing patch size. In an ongoing process of mass extinction, half of the studied mammals have gone extinct. The remaining medium-sized mammal community is highly simplified and homogenized. The persistence of these species in a forest patch is determined by their ability to adapt to a novel simplified diet, the efficient use of the surrounding matrix without being engulfed by the sink effect, and escaping hunting. Our results suggest that the 21st century medium-sized mammalian fauna of this region will comprise only four species unless strict conservation measures are implemented immediately and every forest fragment is effectively protected.
Highlights
The biodiversity crisis that threatens the planet can be considered the sixth major extinction event [1], and tropical forest deforestation is causing extinctions at unprecedented rates [2,3]
We considered a species to be extinct in a forest fragment when we did not detected it during the systematic surveys or in occasional encounters because the fragments are so small, isolated, lacking in food, simplified, and secondarized [22,29,61] that it was almost impossible that the species remained undetected in the fragment
Among the total number of species that appeared to be extinct in the CEPE (48.8%; n = 21) since the beginning of colonization, 41.2% (n = 7) are not referred to either in the ICMBIO list of threatened species [56] or the IUCN Red List [57], while 47% (n = 8) are included in both lists, 5.9% (n = 1) are included only in the IUCN list, and 5.9% (n = 1) only in the ICMBIO list, respectively (Table 1)
Summary
The biodiversity crisis that threatens the planet can be considered the sixth major extinction event [1], and tropical forest deforestation is causing extinctions at unprecedented rates [2,3]. The biota of the future, or the subset of species that will remain after extinction-debts have played out, has already established itself in several areas of the world [4,5], presenting considerably simplified communities whose future is not assured. Mammal species respond in different ways to fragmentation. Large predators, which require extensive home ranges, and have fewer individuals, are the first to disappear [11,12,13,14]. Fragmentation leads to the imminent risk of the sink effect [15], in which individuals try to cross the open matrix in search of suitable habitats, and are killed, which drives the remaining species to extinction. The number of species will decline, reaching a new, less diverse state ([16,17])
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