UBC Theses and Dissertations
Macroecological patterns of biotic interactions and their consequences in prey communities Camacho, Luis
Seventy years after Dobzansky suggested that biotic interactions are more important in the tropics, ecologists are still assembling evidence and elucidating potential mechanisms behind such macroecological patterns. My thesis contributes to this field by demonstrating that predation rates and the strength of mutualistic associations decrease with elevation in the New World tropics. I also tease apart possible mechanisms behind these patterns, which are likely ultimately linked to changes in temperature and productivity with elevation. Using manipulative experiments and field observations across 4000-meter elevational gradients in the equatorial Andes, I show that decreasing predation rates on arthropods at higher elevations are driven by decreasing predator abundance and activity. Ants were responsible for 80% of predation in the lowlands, but were replaced by other predators above 1500m, revealing a parallel qualitative gradient of predation. Along the same gradients, I show that the frequency of ant-hemipteran mutualistic associations also decreases with elevation, driven by a decrease in ant and hemipteran abundance. However, ant abundance limits the interaction above 1500m and hemipteran abundance below, which shaped the resource-consumer dynamics occurring in partner aggregations. I provide evidence that, in response to pervasive ant predation in the lowlands, hemipterans may ‘bribe’ ants with honeydew primarily to dissuade them from predating upon them, rather than, as generally assumed, to obtain their defensive services. This is the first documentation of a mutualistic interaction involving prey offering a reward to predators in exchange for their lives, challenging our fundamental understanding of both mutualism and predation. Finally, I show that anti-predator investment in hemipteran communities does not decrease at the same rate as predation rates at higher elevations, suggesting that the fitness effects of predation may decline at slower rate than predation rates. Hemipteran investment in ant-mutualism across elevations mirrored the contribution of ants to predation further supporting the idea of ant-hemipteran mutualism as an anti-predator strategy from ants themselves.
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