Leaf damage and density-dependent effects on six Inga species in a neotropical forest

Abstract

Many models have been proposed to explain the possible role of pests in the coexistence of a high diversity of plant species in tropical forests. Prominent among them is the Janzen-Connell model. This model suggests that specialized herbivores and pathogens limit tree recruitment as a function of their density or proximity to conspecifics. A large number of studies have tested the predictions of this model with respect to patterns of recruitment and mortality at different life stages, yet only a few have directly linked those density-or distance-dependent effects to pest attack. If pest-attack is an important factor in density-or distance-dependent mortality, there should be spatial heterogeneity in pest pressure. I studied the spatial distribution of leaf damage in saplings of six common Inga species (Fabaceae: Mimosoideae) in the 50ha forest dynamic plot of Barro Colorado Island, Panama. The percent leaf damage of Inga saplings was not heterogeneous in space, and the density of conspecific, congener or confamilial neighbors was uncorrelated with the observed damage levels in focal plants. One of the focal species did suffer density-dependent mortality, suggesting that spatial variation in plant performance in these species is not directly driven by leaf damaging agents. While multiple studies suggest that density-dependent effects on performance are common in tropical plant communities, our understanding of the mechanisms that drive those effects is still incomplete and the underlying assumption that these patterns result from differential herbivore attack deserves more scrutiny. Rev. Biol. Trop. 60 (4): 1503-1512. Epub 2012 December 01.

The chemical ecology of tropical forest diversity: Environmental variation, chemical similarity, herbivory, and richness

“…For example, the Janzen‐Connell hypothesis posits that herbivores may exert density‐dependent effects on plant mortality by feeding preferentially on seeds or plants occurring in dense patches of conspecifics, causing mortality and thereby opening space on the forest floor for the recruitment of additional species (Connell, 1971; Janzen, 1970). This hypothesis has inspired years of study (reviewed by Carson et al, 2008; Comita et al, 2014; Song et al, 2021), but not all data support its predictions (Hyatt et al, 2003; Brenes‐Arguedas, 2012; Song et al, 2021). This may be because, as Janzen himself noted, herbivores do not perceive their would‐be host plants as taxonomic units but rather as chemical entities that may be nutritious or deterrent, depending on their chemistry (Janzen, 1978).…”

Effects of latitude and conspecific plant density on insect leaf herbivory in oak saplings and seedlings

“…Although not directly comparable, this finding contrasts with results from another study, which found that weevil attack rates on acorns of Q. ilex depended on CPD (Bogdziewicz et al, 2018). Further work manipulating seedling densities and separating damage by different insect species is needed for a more detailed and rigorous investigation of herbivore density‐dependent responses in this system (Brenes‐Arguedas, 2012; Abdala‐Roberts et al, 2017). Including other sympatric tree species with broad distributions and manipulating species relative frequencies would also be of high value to describe community‐level patterns and separate intra‐ from interspecific associational effects (sensu Kim and Underwood, 2015).…”

Early establishment and survival of the neotropical dry deciduous forest treeLysiloma microphyllumfrom mountainous Bajio Queretano, Mexico

“…Empirical studies have found that, contrary to predictions, adult conspecifics have stronger effects on seedling mortality in dry (Palamanui, Hawaii, 835 mm of annual rainfall) compared to wet forests (Inman-Narahari et al . 2016), but in certain cases, damage (herbivory) is not correlated with density in tropical rain forests (Brenes-Arguedas 2012). If negative density-dependence increases with rainfall (Comita et al .…”