Communities of insect herbivores foraging on saplings versus mature trees of Pourouma bicolor (Cecropiaceae) in Panama

Abstract

The arthropod fauna of 25 saplings and of three conspecific mature trees of Pourouma bicolor (Cecropiaceae) was surveyed for 12 months in a tropical wet forest in Panama, with particular reference to insect herbivores. A construction crane erected at the study site provided access to tree foliage in the upper canopy. A similar area of foliage (ca. 370 m 2 ) was surveyed from both saplings and trees, but samples obtained from the latter included 3 times as much young foliage as from the former. Arthropods, including herbivores and leafchewing insects with a proven ability to feed on the foliage of P. bicolor were 1.6, 2.5 and 2.9 times as abundant on the foliage of trees as on that of saplings. The species richness of herbivores and proven chewers were 1.5 (n=145 species) and 3.5 (n=21) times higher on trees than on saplings, respectively. Many herbivore species preferred or were restricted to one or other of the host stages. Host stage and young foliage area in the samples explained 52% of the explained variance in the spatial distribution of herbivore species. Pseudo-replication in the two sampling universes, the saplings and trees studied, most likely decreased the magnitude of differences apparent between host stages in this forest. The higher availability of food resources, such as young foliage, in the canopy than in the understorey, perhaps combined with other factors such as resource quality and enemyfree space, may generate complex gradients of abundance and species richness of insect herbivores in wet closed tropical forests.

Contrasting effects of sampling scale on insect herbivores distribution in response to canopy structure

“…Barrios (2003) showed that species richness and abundance of chewing herbivores increased with availability of young leaves in adult trees. Likewise, species richness of polyphagous beetles increases with the availability of young leaves (Basset 2001(Basset , Øde-gaard 2003. The positive correlation of chewing herbivore richness and abundance with leaf density at coarse spatial scale in the present study may be a product of similar mechanism.…”

“…Here we hypothesize that sap-sucking herbivores are strongly dependent on intrinsic characteristics of their host (Lawton 1983, Bernays & Chapman 1994, Denno & Perfect 1994 at small spatial scale, rather than on surrounding canopy traits, probably because sap-sucking insects tend to be more specialized than leaf chewers (see Denno & Perfect 1994, Ødegaard 2003. Conversely, chewers may respond to resource availability at a larger spatial scale as a matter of food and oviposition site diversification (Novotny et al 2002), since such guild tend to be composed by generalists or oligophagous species (Basset 2001, Novotny et al 2002, Ødegaard 2003. These findings further underline both the importance of spatial scale when analyzing insect herbivore diversity, but also the contrasting effect of sampling scale on different herbivore feeding guilds.…”

Light intensity affects spatial distribution of Heteroptera in deciduous forests

“…The upper crown of oaks growing in beech dominated forest contained a higher diversity of Heteroptera than the lower crown. Light availability determines the distribution of leaves within the canopy and vice-versa (Norman & Campbell, 1989;Kucharik et al, 1999) leading to a spatial variation in leaf energy balance, water content and photosynthesis, and therefore in herbivore distribution (Murakami & Wada, 1997;Basset, 2001). According to Ellsworth & Reich (1993) TABLE 5.…”

Insects on Plants: Diversity of Herbivore Assemblages Revisited

“…Stratification studies either compare mass samples among strata without regard to hosts (see Basset et al 2003) or compare the fauna of mature trees with that of conspecific seedlings or saplings (e.g., Barrios 2003, Basset 2001a). Both approaches indicate that the abundance and diversity of herbivorous taxa tend to be higher in the upper canopy than in the understory [with the possible exception of gallers (Cuevas-Reyes et al 2004, Price et al 1998 and that the faunal similarity between the understory and the upper canopy is low.…”