Biodiversity conservation in the hyperdiverse, heterogeneous forests of the western Amazon

Abstract

Tropical nature is under increasing threat from agriculture, and a key question is to what

extent diversified smallholder agriculture is compatible with biodiversity conservation.

This dissertation examines the response of bird and tree communities to smallholder

agriculture in northeastern Peru, home to the world’s richest terrestrial species

assemblages. Despite evidence from elsewhere in the tropics that smallholder agriculture

supports high levels of forest biodiversity, I show that these patterns do not generalize to

western Amazonia, where superlative species richness is associated low-density

populations of habitat-specialist species and remarkable compositional heterogeneity

across space. In Chapter 1, I review how conservationist biology can use explicit

measurements of compositional heterogeneity, or beta diversity, to generalize inference

about biodiversity change from limited field measurements. In Chapter 2, I directly assess

the conservation value of smallholder agriculture in northeast Peru using a field inventory

of birds and trees. Converted examples of different forest habitat types fail to protect the

specialist species unique to each habitat, and the resulting decline in beta diversity drives

a substantial decline in overall regional diversity. In Chapter 3, I explicitly consider the

responses of species that are specialized on poor-soil forest habitats and floodplain forest

habitats. These groups show contrasting responses to smallholder agriculture: poor-soil

specialists decline markedly, while floodplain specialists thrive. In Chapter 4, I place

these results in a broader neotropical context. I show that neotropical bird communities,

due their functional traits, are intrinsically more sensitive to agricultural disturbance in

Amazonia than elsewhere in the neotropics. This difference might be evolutionarily

linked to high species richness in Amazonian birds. In Chapter 5, I use the geological

history of northeastern Peru to provide strong circumstantial evidence that numerous bird

species with patchy populations in the region are connected by ongoing dispersal,

suggesting that dispersal dynamics at large spatial scales might be important for

metapopulation persistence. Taken together, these chapters reveal that western

Amazonia’s hyperdiverse biota is unusually sensitive to agricultural disturbance, and

large intact landscapes are likely crucial for maintaining the world’s richest species

assemblages in the twenty-first century.