Thresholds in the relationship between functional diversity and patch size for mammals in the Brazilian Atlantic Forest

Abstract

Patch size affects abundance and diversity of mammal species, but there is little information on threshold regarding this relationship or relating it to functional diversity. Therefore, we aimed with this study to (1) evaluate if the functional diversity of medium‐ and large‐sized mammal assemblages can be explained by patch size; (2) if this relationship is positive, evaluate whether it is linear (neutral hypothesis) or has critical thresholds (threshold hypothesis); (3) propose specific conservation strategies for each situation. We used primary and secondary mammal database for different forest remnants sizes in the Brazilian Atlantic Forest biome. We calculated functional diversity (FD), using an ecologically meaningful set of traits: body mass and locomotion form, behavioral and dietary traits, and environmental sensitivity of species. We compared linear models with threshold models using Akaike information criterion (AIC). FD values increased with patch size, possibly associated with the high complexity and heterogeneity of larger areas. The threshold model better explained the pattern between FD values and patch sizes than the linear one (delta AIC = 35.8), confirming our threshold hypothesis. Two thresholds (at 60 and 2050 ha) were identified. Our results highlight the need of compliance with the Brazilian Forest Code for assemblages in fragments lower than 60 ha. For assemblages in fragments between the two thresholds whose FD values significantly increased with patch size, we recommend improvements in conservation planning. For assemblages in fragments bigger than 2050 ha, we suggest the establishment of new protected areas, or at least, the maintenance of the existent ones. Our approach can serve as the basis for analysis with other taxonomic groups and ecosystems, increasing chances of maintaining faunal ecological functions, and improving species conservation.

Functional Diversity Metrics: How They Are Affected by Landscape Change and How They Represent Ecosystem Functioning in the Tropics

“…And in the same way that habitat fragmentation can improve some community metrics (such as beta-diversity), it may also have positive consequences for some functional metrics. For example, Magnago et al [11] found functional divergence to decrease with increasing patch size, whereas the majority of authors found an increase with patch size [9,28,32,33]. There are a number of reasons why these results may have been generated.…”

“…The popularity of functional diversity metrics can be seen in the landscape ecology literature, where a number of studies have employed these measures to better understand how landscape change affects communities and ecosystems [9][10][11]. Observed changes to functional diversity metrics are interpreted as direct evidence that rates of ecosystem processes are also affected.…”

“…Patch shape was considered in only two studies, both of which found that more compact patches supported communities with a more diverse array of functions, with higher functional diversity [30] and divergence [39]. (3) Patch size: A positive relationship between patch size and functional richness was found for copro-necrophagous beetles [28], mammals [9], trees [32] and vertebrates [33]. Nonetheless, these results did not hold for all plant communities [11] or birds [34], in which functional richness was found to vary independently of patch size.…”

Fluctuations in bush and rock Hyrax (Hyracoidea: Procaviidae) Abundances Over a 13-Year Period in the Matopos, Zimbabwe

“…Despite not knowing whether (1) breeding performance has changed in the Sandveld following agricultural development and a changing prey base or (2) the differences in breeding productivity between the sites already occurred prior to agricultural transformation of the Sandveld, our findings support the notion that Verreaux's Eagles can maintain good breeding productivity in agriculturally transformed areas. However, there is likely to be a threshold of transformation tolerance whereby functional diversity and prey availability are not compromised (Magioli et al 2015). Land use and climate change are the 2 major pressures facing biodiversity loss globally.…”

Jaguarundi (Puma yagouaroundi) predation by puma (Puma concolor) in the Brazilian Atlantic Forest

“…PECB has high richness and diversity of mammal species (Brocardo et al 2012), being one the most preserved Atlantic Forest remnants, including some threatened species such as Brachyteles arachnoides, Tayassu pecari, Panthera onca and Speothos venaticus, and an important source area of mammals' ecological functions (Magioli et al 2015).…”