Herbivore responses to nutrient enrichment and landscape heterogeneity in a mangrove ecosystem |
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Authors: | Ilka C Feller Anne Chamberlain |
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Institution: | (1) Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD 21037, USA |
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Abstract: | Complex gradients in forest structure across the landscape of offshore mangrove islands in Belize are associated with nutrient
deficiency and flooding. While nutrient availability can affect many ecological processes, here we investigate how N and P
enrichment interact with forest structure in three distinct zones (fringe, transition, dwarf) to alter patterns of herbivory
as a function of folivory, loss of yield, and tissue mining. The effects of nutrient addition and zone varied by functional
feeding group or specific herbivore. Folivory ranged from 0 to 0.4% leaf area damaged per month, but rates did not vary by
either nutrient enrichment or zone. Leaf lifetime damage ranged from 3 to 10% of the total leaf area and was caused primarily
by the omnivorous tree crab Aratus pisonii. We detected two distinct spatial scales of response by A. pisonii that were unrelated to nutrient treatment, i.e., most feeding damage occurred in the fringe zone and crabs fed primarily
on the oldest leaves in the canopy. Loss of yield caused by the bud moth Ecdytolopha sp. varied by zone but not by nutrient treatment. A periderm-mining Marmara sp. responded positively to nutrient enrichment and closely mirrored the growth response by Rhizophora mangle across the tree height gradient. In contrast, a leaf-mining Marmara sp. was controlled by parasitoids and predators that killed >89% of its larvae. Thus, nutrient availability altered patterns
of herbivory of some but not all mangrove herbivores. These findings support the hypothesis that landscape heterogeneity of
the biotic and abiotic environment has species-specific effects on community structure and trophic interactions. Predicting
how herbivores respond to nutrient over-enrichment in mangrove ecosystems also requires an assessment of habitat heterogeneity
coupled with feeding strategies and species-specific behavior measured on multiple scales of response. |
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Keywords: | Aratus pisonii Belize Leaf miners Loss of yield Rhizophora mangle |
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