Disturbances are abrupt events that dramatically alter habitat conditions and resource distribution for populations and communities. Terrestrial landscapes are subject to various disturbance events ...that create a matrix of patches with different histories of disturbance and recovery. Species tolerances to extreme conditions during disturbance or to altered habitat or resource conditions following disturbances determine responses to disturbance. Intolerant populations may become locally extinct, whereas other species respond positively to the creation of new habitat or resource conditions. Local extinction represents a challenge for conservation biologists. On the other hand, outbreaks of herbivorous species often are triggered by abundant or stressed hosts and relaxation of predation following disturbances. These insect responses can cause further changes in ecosystem conditions and predispose communities to future disturbances. Improved understanding of insect responses to disturbance will improve prediction of population and community dynamics, as well as ecosystem and global changes.
We quantified long-term successional trajectories of canopy arthropods on six tree species in a tropical rainforest ecosystem in the Luquillo Mountains of Puerto Rico that experienced repeated ...hurricane-induced disturbances during the 19-yr study (1991–2009). We expected: 1) differential performances of arthropod species to result in taxon- or guild-specific responses; 2) differences in initial conditions to result in distinct successional responses to each hurricane; and 3) the legacy of hurricane-created gaps to persist despite subsequent disturbances. At least one significant effect of gap, time after hurricane, or their interaction occurred for 53 of 116 analyses of taxon abundance, 31 of 84 analyses of guild abundance, and 21 of 60 analyses of biodiversity (e.g., richness, evenness, dominance, and rarity). Significant responses were ~60% more common for time after hurricane than for gap creation, indicating that temporal changes in habitat during recovery were of primary importance. Both increases and decreases in abundance or diversity occurred in response to each factor. Guild-level responses were probably driven by changes in the abundance of resources on which they rely. For example, detritivores were most abundant soon after hurricanes when litter resources were elevated, whereas sap-suckers were most abundant in gaps where new foliage growth was the greatest. The legacy of canopy gaps created by Hurricane Hugo persisted for at least 19 yr, despite droughts and other hurricanes of various intensities that caused forest damage. This reinforces the need to consider historical legacies when seeking to understand responses to disturbance.
Forests provide important ecosystem services—including provision of food, building materials, fresh water, as well as carbon sequestration and climate moderation. Outbreaks of herbivorous insects ...have negative effects on the provision of plant products in the short-term, which are easily measured in terms of lost revenue. Effects on cultural services also are generally negative. However, effects on supporting ecosystem services are complex and include benefits that may compensate for costs, to some extent. For instance, native insect herbivores may function as regulators of forest primary production, maintaining primary production and water and nutrient use within historically sustainable levels. Therefore, “pest” and ecosystem management decisions should consider long-term trade-offs in costs and benefits among ecosystem services.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Forest canopy herbivores are known to increase rates of nutrient fluxes to the forest floor in a number of temperate and boreal forests, but few studies have measured effects of herbivore-enhanced ...nutrient fluxes in tropical forests. We simulated herbivore-induced fluxes in a tropical rainforest in Puerto Rico by augmenting greenfall (fresh foliage fragments), frassfall (insect feces), and throughfall (precipitation enriched with foliar leachates) in replicated experimental plots on the forest floor. Background rates of greenfall and frassfall were measured monthly using litterfall collectors and augmented by adding 10× greenfall or 10× frassfall to designated plots. Throughfall fluxes of NH₄, NO₃ and PO₄ (but not water) were doubled in treatment plots, based on published rates of fluxes of these nutrients in throughfall. Control plots received only background flux rates for these compounds but the same minimum amount of distilled water. We evaluated treatment effects as changes in flux rates for NO₃, NH₄ and PO₄, measured as decomposition rate of leaf litter in litterbags and as adsorption in ion-exchange resin bags at the litter–soil interface. Frass addition significantly increased NO₃ and NH₄ fluxes, and frass and throughfall additions significantly reduced decay rate, compared to controls. Reduced decay rate suggests that nitrogen flux was sufficient to inhibit microbial decomposition activity. Our treatments represented fluxes expected from low–moderate herbivore outbreaks and demonstrated that herbivores, at these outbreak levels, increase ecosystem-level N and P fluxes by >30% in this tropical rainforest.
The fall webworm, Hyphantria cunea (Drury) (Lepidoptera: Erebidae), is a widespread defoliator that is native throughout the continental United States, as well as southern Canada and northern Mexico. ...It has been introduced accidentally into many parts of Europe and Asia. Larvae have been recorded from >400 species of forest and shade trees, primarily hardwoods, but also several conifer species in the southern United States. This species is of minor importance in forests, but can cause serious losses in pecan and fruit tree orchards and is a major nuisance in urban parks and homelots where it often completely defoliates ornamental and shade trees. Fall webworm larvae construct conspicuous webs that start at the ends of branches and expand as the larvae grow to incorporate multiple branches. Foliage within webs is completely consumed. Two color races occur throughout the range of this moth, but pure white adults and black-headed larvae predominate in northern regions, whereas spotted adults and red-headed larvae predominate in southern regions. Populations of fall webworm are regulated naturally in its native range by host quality and abundance and by at least 50 species of dipteran and hymenopteran parasitoids and 36 species of predators and parasites. Physical removal, biocontrol, and insecticides are available for management of this moth.
Natural ecosystems provide a variety of services on which humans, and other organisms, depend for survival and well-being. These ecosystem services can be categorized as provisioning (production of ...food, fiber, water and other resources), cultural (non-material benefits, such as recreation, spiritual and other aesthetic values), supporting (primary production, pollination, decomposition and soil formation necessary for resource production) and regulating (biological control and other feedback mechanisms that maintain relatively consistent delivery of services). Ecosystems also have been viewed as producing “disservices”, such as pests, litter, biological hazards such as diseases, animal attacks, allergenic and poisonous organisms, and geophysical hazards such as floods and storms. Many of these disservices are induced by management practices such as deforestation and concentration of agricultural crops. Insects affect ecosystem services in a variety of ways, positively and negatively. The papers in this special issue are focused on managing insects and ecosystems, and their interactions, in ways that ensure sustainability of ecosystem services and that minimize induction of disservices.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Abstract
Leafcutting ants are primarily a tropical group, but three species, particularly the Texas leafcutting ant, Atta texana (Buckley) (Hymenoptera: Formicidae), occur in the southern United ...States. Leafcutting ants provide an example of the complexity of ecological interactions. As a result of extensive defoliation and nest excavation, these ants influence vegetation cover, soil structure, and water fluxes over a significant portion of the landscape. They also can be severe forest and crop pests, and collapse of their extensive underground colonies can undermine roads and structures. In Texas, they are considered the second most important pest in pine plantations, following southern pine beetle, Dendroctonus frontalis Zimmerman (Coleoptera: Curculionidae). Leafcutting ants can defoliate a wide variety of plants, but some plant species are unpalatable because of defensive chemicals or endophytic fungi growing within foliage. Leafcutting ant populations also are regulated naturally by the availability of suitable nest sites and by predators, parasites, and antagonists of their fungal gardens. Relatively few management options are available. One bait and one fipronil product are labeled for leafcutting ant control.
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