Herbivory, growth rates, and habitat specialization in tropical tree lineages: implications for Amazonian beta‐diversity

Abstract

Abstract. Tropical plant diversity is extraordinarily high at both local and regional scales. Many studies have demonstrated that natural enemies maintain local diversity via negative density dependence, but we know little about how natural enemies influence beta-diversity across habitats and/or regions. One way herbivores could influence plant beta-diversity is by driving allocation trade-offs that promote habitat specialization across resource gradients. We therefore predicted that increasing resource availability should be accompanied by increasing herbivory rates and decreasing plant allocation to defense. Second, relative abundances within plant lineages are predicted to reflect patterns of habitat specialization and allocation tradeoffs. A phylogenetic context is vital not only to compare homologous plant traits (including defense strategies) across habitat types, but also to connect evolutionary trade-offs to patterns of species diversification in each phylogenetic lineage.We tested these predictions for trees in white-sand, clay terra firme, and seasonally flooded forests in Peru and French Guiana that represent the range of soil fertility, forest structure, and floristic compositions found throughout the Amazon region. We established 74 0.5-ha plots in these habitats and sampled all trees. Within 12 representative plots we marked newly expanding leaves of 394 saplings representing 68 species, including the most abundant species in each plot in addition to species from five focal lineages: Swartzia and Inga (Fabaceae), Protieae (Burseracaeae), Bombacoideae (Malvaceae), and Micropholis (Sapotaceae). We measured total leaf production rates for each sapling and calculated relative herbivory impact as the ratio between herbivory rate and leaf production rate.Herbivory rates averaged 2.1% per month, did not correlate with leaf production rate, and were similar across habitats. Relative herbivore impacts exceeded leaf production rates for most species. Leaf production rate averaged 2.8%, was significantly higher in seasonally flooded forests than the other two habitats, and exhibited significant correlations with specific leaf area. Species with high herbivory rates exhibited significantly lower relative abundances in terra firme forests. Overall, focal species within lineages present contrasting patterns regarding their herbivory rates and leaf production rate within habitats. These results highlight why a lineage-based approach is necessary when attempting to connect hypotheses regarding evolutionary trade-offs to community assembly patterns.

Predicting tropical insect herbivore abundance from host plant traits and phylogeny

“…Recent ecological studies of plant-herbivore interactions have argued for the importance of phylogenetic context to identify the mechanisms responsible for patterns in trophic relationships (Lamarre et al 2012). Although this may be the case for particular plant defenses (Fine et al 2006, Agrawal et al 2009a) and the dietary specialization of particular herbivore species (Weiblen et al 2006), the overall abundance of leafchewing herbivores and most of the leaf traits we examined showed little evidence of phylogenetic signal (Table 3).…”

“…Diverse tropical forests have been particularly fertile ground for testing theories on mechanisms of species coexistence in communities (Wright 2002) where trophic interactions may affect patterns of plant community phylogenetic diversity (Lamarre et al 2012). The idea that density-dependent processes involving specialized pests and pathogens could limit the recruitment of related plants in close proximity is not new (Janzen 1970, Connell 1971.…”

“…For example, rapid leaf expansion (Coley and Aide 1991) and delayed greening (Kursar and Coley 1992) have been regarded as plant adaptations that limit herbivory and nutrient loss. Evidence that evolved defenses play a role in mediating plant-herbivore interactions (Agrawal 2005) has supported the view that a phylogenetic context is needed to test predictions about trophic relationships (Lamarre et al 2012). The distribution of herbivore dietary preferences with respect to plant community phylogeny has further suggested that many tropical insect species are clade specialists (Tavakilian et al 1997, Berkov and Tavakilian 1999, Novotny et al 2002, 2004, 2010, Novotny and Basset 2005, Odegaard et al 2005, Weiblen et al 2006, Dyer et al 2007, Hulcr et al 2007).…”

Changes in the background losses of woody plant foliage to insects during the past 60 years: are the predictions fulfilled?

“…Insect herbivory affects the productivity of ecosystems, modifies nutrient cycling, maintains the diversity of plant communities and influences a number of ecosystem services [1,2]. Consequently, the relationships between plants and insects are among the most intensively studied biotic interactions [3,4], and the exploration of changes in insect-plant relationships caused by the abiotic drivers of global change has become increasingly popular during the past decades.…”

Niche evolution across spatial scales: climate and habitat specialization in California Lasthenia (Asteraceae)

“…At these local scales, we can explore niche evolution by pruning the clade of interest to those taxa that co-occur in a local area: the scale at which it is possible to collect detailed data on the distribution, abundance, ecophysiology, and environmental correlates of the lineages of interest (e.g., Cavender-Bares et al 2004, Slingsby and Verboom 2006, Graham et al 2012, Savage and Cavender-Bares 2012. An alternative to the clade-based approach is a community-based methodology that examines the phylogenetic structure of a group of distantly related, but closely interacting species within a community or community type (e.g., Silvertown et al 2006, Swenson et al 2007, Dinnage 2009Eaton et al 2012, Lamarre et al 2012. Studies assuming a community-based approach have illuminated the relative importance of phylogenetic and niche differentiation in structuring communities, but provide less power to investigate how niche axes evolve across speciation events throughout the diversification of a clade.…”