Abstract
The Janzen-Connell hypothesis states that tree diversity in tropical forests is maintained by specialist predators that are distance- or density-responsive (i.e. predators that reduce seed or seedling survival near adults of their hosts). Many empirical studies have investigated whether predators are distance-responsive; however, few studies have examined whether distance-responsiveness matters for how predators maintain tree diversity. Using a site-occupancy model, we show analytically that distance-responsive predators are actually less able to maintain diversity than specialist predators that are not distance-responsive. Generally, specialist predators maintain diversity because they become rare when their host's densities are low, reducing predation risk. However, if predators are distance-responsive, and most seeds cannot disperse away from these predators, then seed predation rates will remain high, even if predator density is low across the landscape. Consequently, a reduction in a host's population density may not lead to a significant reduction in seed and seedling predation. We show that habitat partitioning can cause recruitment to be highest near conspecific adults, even in the presence of distance-responsive predators, without any change in the effect that the predators have on coexistence (a result contrary to predictions of the Janzen-Connell hypothesis). Rather, specialist predators and habitat partitioning have additive effects on species coexistence in our model, i.e., neither mechanism alters the effect of the other one.
Original language | English (US) |
---|---|
Pages (from-to) | 60-70 |
Number of pages | 11 |
Journal | Theoretical Population Biology |
Volume | 106 |
DOIs | |
State | Published - Dec 1 2015 |
Keywords
- Coexistence
- Fitness-density covariance
- Habitat partitioning
- Janzen-Connell hypothesis
- Predator partitioning
- Spatial storage effect
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics