Paradoxically, agricultural practices constitute both the greatest driver of biodiversity loss and also the greatest opportunity for conservation, given the shrinking scope of protected areas in many regions. Recent studies document the significant biodiversity, across many taxa and biomes, that agricultural landscapes can support over the short term. Yet little is known about the long-term effects of alternative agricultural practices on ecological communities. To investigate long-term biodiversity responses to habitat conversion, we quantified temporal shifts in avian communities across forest and countryside landscapes in Costa Rica using 18-yrs of repeated surveys (281,415 detections of 510 bird species). We addressed four questions. First, does the magnitude of long-term change in avian communities differ between natural forests and agricultural lands? Second, are these long-term changes driven by gradual shifts in species composition between years or rather by abrupt shifts in the identity and abundance of community members present? Third, we ask how land cover type interacts with seasonal dynamics to drive observed patterns of biodiversity change. Finally, how do different avian guilds compare in driving long-term shifts in community structure in agricultural landscapes?
Results/Conclusions
Here we show pronounced, long-term directional shifts in bird communities in agriculture and particularly in intensive monocultures, with mild shifts in diversified farming systems as compared to natural forests. Contrary to other well studied farmland bird communities, all communities were remarkably constant in species richness and abundance over the 18 yrs, yet all varied through time in species composition. As expected, the rate and magnitude of change were highest in intensive monocultures. In addition, the communities of intensive monocultures lost the rhythmic wet-season–dry-season dynamics characterizing natural forests and diversified agriculture. All major guilds, including those involved in pest control, pollination, and seed dispersal, showed striking changes over time. Our findings demonstrate clearly that diversified agriculture offers a pathway for securing biodiversity and associated ecosystem services into the first phase of the Anthropocene.