Deforestation Simplifies Understory Bird Seed-Dispersal Networks in Human-Modified Landscapes

Abstract

Global biodiversity is threatened by land-use changes through human activities. This is mainly due to the conversion of continuous forests into forest fragments surrounded by anthropogenic matrices. In general, sensitive species are lost while species adapted to disturbances succeed in altered environments. However, whether the interactions performed by the persisting species are also modified, and how it scales up to the network level throughout the landscape are virtually unknown in most tropical hotspots of biodiversity. Here we evaluated how landscape predictors (forest cover, total core area, edge density, inter-patch isolation) and local characteristics (fruit availability, vegetation complexity) affected understory birds seed-dispersal networks in 19 forest fragments along the hyperdiverse but highly depauperate northeast distribution of the Brazilian Atlantic Forest. Also, our sampled sites were distributed in two regions with contrasting land cover changes. We used mist nets to obtain samples of understory bird food contents to identify the plant species consumed and dispersed by them. We estimated network complexity on the basis of the number of interactions, links per species, interaction evenness, and modularity. Our findings showed that the number of interactions increased with the amount of forest cover, and it was significantly lower in the more deforested region. None of the other evaluated parameters were affected by any other landscape or local predictors. We also observed a lack of significant network structure compared to null models, which we attribute to a pervasive impoverishment of bird and plant communities in these highly modified landscapes. Our results demonstrate the importance of forest cover not only to maintain species diversity but also their respective mutualistic relationships, which are the bases for ecosystem functionality, forest regeneration and the provision of ecological services.

Structural changes and carbon reduction due to habitat loss in Atlantic Forest

“…Thus, reducing the abundance of these families may influence the functioning of different mutualistic processes and may lead to cascading extinctions of various animal groups (Bennett et al, 2009;Kurten, 2013). In fact, Pinto et al (2021) found a reduction in interactions between frugivorous birds and fleshy fruit plants and simplified bird-plant interaction networks in landscapes with small forest amounts in the same biome. Moreover, they assume that the impoverishment of birds and plant communities was responsible for that pattern.…”

Land‐use homogenization reduces the occurrence and diversity of frugivorous birds in a tropical biodiversity hotspot

“…Understanding how frugivorous birds are affected by changes in land use is urgently necessary because they comprise the main group of seed dispersers across tropical forests, although they exhibit the greatest extinction rates among birds (Şekercioğlu et al, 2004). Consequently, the loss of frugivores can trigger further extinction cascades (Rogers et al, 2021), disrupting key ecological processes such as seed dispersal (Menezes Pinto et al, 2021; Vidal et al, 2019). Thus, understanding how frugivorous birds respond to land‐use change is crucial to foreseeing ecosystem functioning alteration in human‐modified landscapes.…”