Availability Of Invertebrate Prey Research Articles

Measuring the Impact of Parental Foraging by Starlings (Sturnus vulgaris) on Soil Invertebrate Prey Availability: An Exclosure Experiment

Depletion of soil invertebrate availabilities by starling foraging during the breeding season was investigated by using exclosures to create areas where the birds could not feed. A field 'preferred' by the wild birds was compared with a 'non-preferred' field. Prey biomass was measured from soil cores and the foraging success of individuals feeding in experimental enclosures gave a measure of prey availability. Foraging by these birds resulted in significant short-term depletion after a few hours of foraging. Trials conducted after a 24-h interval showed that this depletion was due to removal of prey by the birds rather than invertebrate movements. Comparison with exclosure sites at the end of the chick-feeding period showed that foraging by the wild birds caused significant long-term depletion. This depletion was greatest in the 'preferred' field, which offered a higher availability of leatherjackets Tipula paludosa. The 'non-preferred' field yielded lower capture rates, despite a higher earthworm biomass in the soil cores. These findings suggest that soil core analysis alone is insufficient to predict the foraging success of starlings and other birds feeding on soil invertebrates. The significant reduction in prey availability to parent starlings is discussed in relation to the number of parental foraging trips made to the two fields.

Ecology of a saline stream: community responses to spatial gradients of environmental conditions

Spatial changes in structural and functional characteristics of fish and macroinvertebrate communities in eastern Kentucky were investigated in a drainage system chronically exposed to high levels of chloride salts from nearby oilfield operations. Salinity levels at biological monitoring stations ranged from 0.12–31.3‰. Lotic regions with salinities greater than 10‰ were dominated by larvae of the dipterans Ephydra and Culicoides. In regions with salinities less than 10‰ species richness increased more or less linearly with decreasing levels of chloride salts. Ephemeropterans appeared to be one of the major invertebrate groups least tolerant of elevated NaCl levels and were absent in regions with salinities greater than 2‰ Availability of food resources, such as periphyton and particulate organic matter, did not appear to be grossly altered in disturbed regions, and it is suggested that the observed distribution of macroinvertebrate fauna was largely in response to taxonomic differences in salt tolerance. Fish seemed to be more tolerant of highly saline conditions, and several species were observed in regions experiencing salinities as high as 15‰. Accordingly, assemblages of fish taxa along the salinity gradient may have been influenced by trophic factors, such as spatial limitations in availability of invertebrate prey.

Ontogenetic diet shifts and resource partitioning among piscivorous fishes in the Venezuelan ilanos

Resource utilization by nine abundant piscivores from a diverse tropical fish assemblage was examined over the course of a year. All nine species exhibited peak reproduction during the early wet season and a similar sequence of size-dependent shifts from a diet composed primarily of microcrustacea, to aquatic insects, and finally fishes. Three piranha species specialized on fish fins, particularly at subadult size classes (SL 30–80 mm). Gradual dessication of the floodplain during the transition season was associated with fish growth, increased fish density, and decreased aquatic primary productivity and availability of invertebrate prey. Based on 118 resource categories, average pairwise diet overlap was low during all three seasons: wet, transition, and dry. Of 72 species pairings, only one pair of fin-nipping piranhas exhibited high overlap simultaneously on three niche dimensions: food type, food size, and habitat. Adults of two species, a gymnotid knifefish and pimelodid catfish, were largely nocturnal. Patterns of habitat utilization indicate that piranhas may restrict diurnal use of the open-water region by other piscivores. Collective diet overlap of individual piscivore species with the other eight feeding guild members and collective overlaps with the entire fish community each revealed two basic seasonal trends. Four species that showed an early switch to piscivory also showed a high degree of diet separation with both the guild and community at large on a year-round basis. The five remaining species showed lowest collective diet overlaps during the transition season when availability of invertebrates was reduced and fish densities were maximal. Whereas predation may play a role in habitat separation, diffuse competition for food resources during the approximately four-month transition season probably is the principal factor yielding patterns of diet specialization.

Effects of Urbanization on the Salamander Desmognathus Fuscus Fuscus

Five spring—fed streams near Atlanta, Georgia, comprise an urbanization gradient ranging from severely distributed to undistributed conditions. Population densities of the dusky salamander, Desmognathus fuscus fuscus, were estimated within these streams and were inversely proportional to the degree of urbanization. Differences in the chemical parameters among the stations, while reflecting habitat disruption, were not considered limiting factors on salamander densities. Analysis of invertebrate prey availability indicated no significant difference among the stations. Salamander populations were significantly affected by scouring caused by increased runoff and soil erosion in disturbed areas. Differences in salamander densities were also attributed to relative stability of the bank soils and availability and dispersal of protective cover. More cohesive substrates and increased availability of ground cover at the less distributed areas offered greater stability against erosion and better habitats for salamander burrowing. Urbanization thus creates physical instability within stream habitats. Such instability results in a disruption of trophic structure by a reduction or loss of this major stream predator.