Leaf traits mediate changes in invertebrate herbivory along broad environmental gradients on Mt. Kilimanjaro, Tanzania

Abstract

Temperature, primary productivity, plant functional traits, and herbivore abundances are considered key predictors of leaf herbivory but their direct and indirect contributions to community‐level herbivory are not well understood along broad climatic gradients. Here, we determined elevational herbivory patterns and used a path analytical approach to disentangle the direct and indirect effects of climate, land use, net primary productivity (NPP), herbivore abundance, and plant functional traits on community‐level invertebrate herbivory along the extensive elevational and land use gradients at Mt. Kilimanjaro, Tanzania. We recorded standing leaf herbivory caused by leaf chewers, leaf miners and leaf gallers on 55 study sites distributed in natural and anthropogenic habitats along a 3,060 m elevation gradient. We related the total community‐level herbivory to climate (temperature and precipitation), NPP, plant functional traits (specific leaf area, leaf carbon‐to‐nitrogen [CN] ratio and leaf nitrogen‐to‐phosphorus [NP] ratio) and herbivore abundances. Leaf herbivory ranged from 5% to 11% along the elevation gradient. Total leaf herbivory showed unimodal pattern in natural habitats but a strongly contrasting bimodal pattern in anthropogenic habitats. We also detected some variation in the patterns of leaf herbivory along environmental gradients across feeding guilds with leaf chewers being responsible for a disproportionally large part of herbivory. Path analyses indicated that the variation in leaf herbivory was mainly driven by changes in leaf CN and NP ratios which were closely linked to changes in NPP in natural habitats. Similarly, patterns of leaf herbivory in anthropogenic habitats were best explained by variation in leaf CN ratios and a negative effect of land use. Our study elucidates the strong role of leaf nutrient stoichiometry and its linkages to climate and NPP for explaining the variation in leaf herbivory along broad climatic gradients. Furthermore, the study suggests that climatic changes and nutrient inputs in the course of land use change may alter leaf herbivory and consequently energy and nutrient fluxes in terrestrial habitats.

Interactions of gall‐formers and leaf‐chewers on a tropical tree fern: evidence for non‐repulsion and co‐occurrence between insect guilds

“…Nitrogen content was almost 20% lower in galled samples, and similar results have been reported for other galled plant species (Hartley 1998). Galls also promoted sinks for several nutrients in other studies (Fernandes & Santos 2014), and because herbivores are attracted to higher leaf N concentrations (see Mattson 1980;Stiegel et al 2017), as well as lower C/N levels (Njovu et al 2019), nutrient sinks and altered nutrient balances typically impair subsequent leaf chewers on galled angiosperms (see Prior & Hellmann 2010). We conclude that in our study, N content did not differ enough between galled and non-galled samples to cause an increase in attacks of sawflies on non-galled tissues.…”

Beneficial insects are associated with botanically rich margins with trees on small farms

“…Fields were selected from four agro-ecological zones (agriculturally intense mid-elevation in Bunda, Malawi; low elevation zone, Tanzania (< 1000 m); mid elevation zone, Tanzania (1000–1500 m); high elevation zone, Tanzania (> 1500 m)). The three zones in Tanzania represented a gradient of climates and growing conditions 44 but were all of tropical highland climate with annual rainfall of 600 to 2000 mm (increasing with elevation) and a bimodal rainfall peak 10 . The Malawian zone was of subtropical highland climate with annual rainfall of 700 mm concentrated in a unimodal peak.…”

Herbivory and leaf traits of two tree species from different successional stages in a tropical dry forest

“…The higher content of N in the leaf seems to be a fundamental aspect for leaf consumption. This relationship has been observed in many ecosystems, including tropical dry forests [58,[66][67][68]. The Principal Component Analysis showed the formation of groups in relation to successional stages; thus, the herbivory rate indicates to be higher in environments where the investment in defensive traits was lower and the nutritional quality of the leaves was higher [2,44].…”