Research About insects

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Effect of herbivores on Sitka willow and associated plant and animal communities and soils.

The invasion of trees and shrubs in early succession is often transformative because of their potential to outcompete early pioneers, provide animal habitat, influence nutrient cycling, and occupy sites over long time spans. The extent to which insect herbivores influence such successional transitions is unknown. We are investigating whether herbivory by a pair of stem-boring insects may substantially impede the structural dominance of Salix sitchensis, the first abundant woody colonist on a large primary successional site at Mount St. Helens volcano, Washington, USA. We also quantify vegetation and soil development at these same sites. Our collaborator Charlie Crisafulli (USFS) quantifies bird use of these sites, eventually allowing us to link herbivore effects on vegetation to bird habitat.

 

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Insect colonization and invasion in the recovering devastation zone of Mount St. Helens.

Vegetation patches at Mount St. Helens represent discrete islands that are a focus for interactions among plants and insects. Our continuing studies focus on the role of biotic interactions (plant-herbivore and predator-prey), dispersal, and disturbance in this highly fragmented landscape. In the 1997 field season, we aim to address two primary questions: 1) What factors have allowed exotic ladybird beetles to displace native ladybird species within the monument? and 2) How does the size of vegetation patches influence colonization by insect species?

 

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Ant-plant interactions at Mount St. Helens

Within the blowdown zone of Mount St. Helens, Formica pacifica is the most common ant species. From studies during the summer of 1991 patterns were observed in the spatial dispersion of F. pacifica nests and also in the plant species present on the middens of these nests. Formica pacifica is less active within species rich vegetation patches than in exposed areas. Studies in 1992 will investigate whether F. pacifica nests are more common along the edges of vegetation patches. Other studies will investigate the presence of Hypochaeris radicata (false dandelion) on the middens of these nests. The wind born seeds of H. radicata may have difficulty establishing on the nutrient poor tephra. Ant middens may provide suitable sites for these plants to establish. Soil brought to the surface during nest excavation and the collection of plant and insect parts may add nutrients to the substrate of ant middens. Once established above an ant nest, plants would begin to cause shading of the nest. The resulting decrease in temperature may cause the ants to move their nest location. By moving out away from the shade of a vegetation patch and creating more sites for plant establishment, ants of F. pacifica may be effecting the expansion of vegetation patches. Since primary succession at Mount St. Helens is a slow process, the seemingly insignificant effect of ants on this process may be relatively important.

 

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Community reassembly following volcanic disturbance: the ground dwelling beetles (Coleoptera)

This study documents the recovery of beetles within the volcanically disturbed areas of Mount St. Helens and should provide an index to the rate and stage of ecosystem recovery at various points in time since the eruption. Beetles are ideal for monitoring ecological recovery following disturbance as they represent a broad trophic array. The ground dwelling beetle fauna of forests and clearcut habitats were sampled using pitfall traps (10 traps/site) that were open from the time of spring snow melt to early autumn from 1982-1984 and again in 1987 and 1990. Sites sampled include undisturbed “reference” areas and three post-eruption habitats (ashfall, blowdown, and pyroclastic/debris flow).

 

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Ecological factors determining population size of Aphis varians.

Research is intended to assess the ecological factor(s) of greatest importance in determining the population size of an aphid (Aphis varians) feeding on fireweed (Epilobium angustifolium). We manipulated the host plant (by shading, watering, and fertilizing), the size of fireweed patches, the density of a leaf-feeding beetle (Altica tombacina) which also utilizes fireweed, and the presence of predators of the aphid (primarily ladybird beetles and syrphid flies) by means of cages.

 

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Recovery of aquatic insect communities in streams near Mount St. Helens

We have monitored stream insect communities from 1980 to 1988 in Clearwater Creek, Elk Creek, and Ape Canyon. Quantitative and qualitative samples indicate rapid colonization in 1981-82, and then a gradual increase in richness and diversity. Over 200 taxa have now been collected from Ape or Clearwater Creeks.

 

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Population ecology of the aphid Aphthargelia symphoricarpi on Mount St. Helens

I have examined the ecology of the aphid Aphthargelia symphoricarpi in terms of its interactions with its host plant Polygonum newberryi and its major predator, the ant Formica fusca. My approach involves a combination of field experimentation and observation with mathematical modelling.

 

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Ecosystem recovery on the debris avalanche

The object of this study is to monitor ecosystem recovery on the debris avalanche created by the May 1980 eruption of Mount St. Helens. Vegetation was significantly reduced in the blast area. Plant survival and diversity was apparently related to growth form. Plants with underground dormant buds survived best. Plant recovery has been correlated with moisture rather than physical structure of the substrate.

 

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Arthropod recolonization of Mount St. Helens.

Ashfall and blast zone sites have been sampled in order to monitor the recovery of insect and spider populations reduced by the May 1980 eruption. There were many survivors of the eruption in ashfall sites, especially of sedentary species and others that were protected in micro-refugia. Mortality in arthropod populations was correlated with the depth of the ashfall. Using ant colonies as an index, areas with 15 cm or less of ash deposited had species numbers similar to sites outside the devastated area. However in all areas arthropod populations have remained low compared to arthropod population recovery following clearcutting.

 

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