Adaptation and latitudinal gradients in species interactions: nest predation in birds

Are rates of biotic interactions are stronger in the tropics? Here we
investigate nest predation rates in birds, a canonical example of a strong
tropical biotic interaction. Counter to expectations, daily rates of nest
predation vary minimally with latitude. However, life history traits that
influence nest predation have diverged between latitudes. For example,
tropical species have evolved a longer average nesting period, which is
associated with reduced rates of nest attendance by parents. Daily nest
mortality declines with nesting period duration within regions, but
tropical species have a higher intercept. Consequently, for the same
nesting period length, tropical species experience higher daily nest
predation rates than temperate species. The implication of this analysis
is that the evolved difference between latitudes in nesting period length
produces a flatter latitudinal gradient in daily nest predation than would
otherwise be predicted. We propose that adaptation may frequently dampen
geographic patterns in interaction rates.