Gary W. Barrett

Succession in Old-Field Plant Communities: Effects of Contrasting Types of Nutrient Enrichment

We investigated the effects of monthly nutrient applications on succession in two old-field plant communities. Succession was monitored for 3 yr in 1-yr (younger) and 4-yr (older) experimental plots. Three 0. 1-ha plots in each old field were treated with sludge, three with fertilizer, and two were left as untreated controls. In the younger community, herbaceous perennials and winter annuals replaced summer annuals by the 3rd yr of succession in control plots. Summer annuals, however, dominated enriched plots throughout the study. Species richness was significantly higher in enriched plots than in control plots during the 1st yr, but was significantly lower than control plots thereafter. Annual aboveground net primary productivity (ANPP) was significantly greater in enriched plots than in controls in the 1st yr, but the converse occurred in the 3rd yr. The type of nutrient enrichment affected ANPP; sludge plots had significantly lower ANPP than fertilizer plots in the 1st and 3rd yr. In the older community, two summer annuals and a biennial displaced dominant perennial grasses in enriched plots. In contrast to the younger community, ANPP was consistently greater in nutrient-enriched plots than in controls, and nutrient enrichment did not alter species richness. The type of nutrient enrichment affected the older community in an opposite manner from the younger community; sludge plots had significantly greater ANPP than fertilizer plots in the 3rd yr. We concluded that the age and physiognomy of the old-field community, the type of nutrients applied, and the duration of enrichment, each influenced the course of succession; responses observed in the 1st yr of enrichment were not indicative of later trends.

Effects of corridor width and presence on the population dynamics of the meadow vole (Microtus pennsylvanicus)

We tested the effects of increased landscape corridor width and corridor presence on the population dynamics and home range use of the meadow vole (Microtus pennsylvanicus) within a small-scale fragmented landscape. Our objective was to observe how populations behaved in patchy landscapes where the animals home range exceeded or equaled patch size. We used a small-scale replicated experiment consisting of three sets of two patches each, unconnected or interconnected by 1-m or 5-m wide-corridors, established in an old-field community (S.W. Ohio). Control (0-m) treatments supported significantly lower vole densities than either corridor treatment. Females were the dominant resident sex establishing smaller home ranges (<150m2) than males (>450m2). Significantly more male voles dispersed between patches with corridors than between patches without corridors. However, no difference was observed regarding the number of male voles dispersing between patches connected by corridors when compared to the number dispersing across treatments. Dispersal between connected patches was restricted to corridors based on tracking tube data. Corridor presence was more important than corridor width regarding the movement of male voles within their home range.

Inbreeding Avoidance Increases Dispersal Movements of the Meadow Vole

This study tested whether inbreeding avoidance could influence the frequency and timing of dispersal movements in a small microtine rodent, the meadow vole (Microtus pennsylvanicus). Meadow voles released into experimental grassland plots with siblings were more likely to disperse from these plots than were voles released into similar plots with nonsiblings. Furthermore, voles that dispersed from siblings groups did so sooner than dispersing voles from nonsiblings groups. Voles released with nonsiblings were recaptured within the plots for longer periods than were voles from siblings groups. Males from both groups remained within the plots for shorter times than did females, but the degree of this sex bias was greater for siblings groups. Thus, it appears that inbreeding avoidance can influence dispersal movements of the meadow vole and may be partially responsible for patterns of male—biased dispersal in at least some mammals.

The Effects of Two Acute Stresses on the Arthropod Component of an Experimental Grassland Ecosystem

The effects of two acute stresses, mowing and burning, on the arthropod component of an experimental grassland ecosystem were investigated. Oats (Avena sativa L.) were planted in two comparable and adjacent 1-acre areas. Midway in the growing season (July), one area was mowed and the other areas was both mowed and burned. Density and biomass were used to measure the effects of both stresses on the total arthropod community, while species diversity and equitability were used to analyze the species composition and apportionment of the Coleoptera. Effects of mowing on arthropod density and biomass appeared to be relatively brief (2 weeks) as compared with those of burning (3 months). This difference was attributed to a shift from live primary producer energy to detritus in the mowed area, as compared to the almost complete destruction of the energy source in the burned area. Coleoptera species/area diversity was significantly lower (P < 0.01) in the burned area. This was attributed to a greater energy supply and a larger number of ecological niches in the unburned grid. Margalefs species diversity, D = (S-1)/1nN, for the total Coleoptera community was significantly reduced (P < 0.05) in response to the fire. When analyzed by trophic levels on a long-term basis, herbivorous Coleoptera species diversity was significantly reduced (P < 0.01), whereas that of the carnivorous Coleoptera was not measurably affected. Herbivorous Coleoptera equitability values, in response to mowing, exhibited a brief increase before returning to the premow level. In response to burning, however, herbivorous Coleoptera equitability values remained higher than those in the unburned area, indicating a longterm limitation of resources. Carnivore equitability values did not exhibit a long-term increase in response to the fire stress. Coleoptera responses to fire revealed that biomass, species/area diversity, and primary consumer species diversity and equitability were the most sensitive indicators for evaluating the effects of an acute environmental stress such as fire. Coleoptera responses appeared to be representative of the total arthropod community.

Effects of habitat patch shape on population dynamics of meadow voles (Microtus pennsylvanicus)

The geometry of habitat patches may affect population dynamics due to differences in edge-to-area ratios for patches of different sizes and shapes. We conducted a field experiment replicated over 2 years employing four square (40 by 40 m) and four rectangular (16 by 100 m) habitat patches of equal size (1,600 m2) to determine the effects of contrasting shapes of habitat patches on population dynamics of meadow voles ( Microtus pennsylvanicus ). We tested the predictions that dispersal rates would be higher, home ranges larger, and population densities lower in rectangular patches compared to square patches. The number of dispersers, but not dispersal rates, was greater in rectangular patches than in square patches only when densities of voles were low. Home ranges were of equal area but different shape in the contrasting shapes of patches. Population density, recruitment, body mass of dispersers, body mass of residents, survival, and age structure were largely unaffected by differences in patch shape. Thus, plasticity of behavior (e.g., changes in shape of home range) appears to have prevented differences in population dynamics between the two patch shapes. We conclude that patch shape does not markedly affect the population dynamics of the meadow vole, and that this species appears to be an edge-tolerant species.

Effects of vegetation and hydrologic load on sedimentation patterns in experimental wetland ecosystems

Vegetation and water velocity effects on patterns of sediment deposition were tested by monitoring sedimentation rates in dense cattail, open water, and transitional vegetation zones at distances of 5, 10, and 20 m from the inflows of two experimental wetland basins at the Des Plaines River Wetlands Demonstration Project, northeastern Illinois, USA. One basin received a high hydrologic load (up to 50 cm/wk) and one basin received a low load (up to 6 cm/wk). Sediment deposition rates within 20 m of the inflows reached 3300 g dry wt m−2 day−1 in the high-load basin and 700 g dry wt m−2 day−1 in the low-load basin. Vegetation patterns did not have a significant effect (P > 0.05) on sediment deposition rates in the high-load basin, whereas water velocity effects on rates of sedimentation were significant (P < 0.01) in three of four periods of monitoring. In the low-load basin, vegetation effects were significant (P < 0.01) during the entire period of investigation. Experimental research at this scale aids in the assessment of design criteria for constructed wetlands.

Effects of Resource Partitioning on the Population Dynamics and Energy Utilization Strategies of Feral House Mice (Mus Musculus) Populations Under Experimental Field Conditions

Eight 0. 1-ha small-mammal enclosures were stocked with house mice (Mus musculus) on 6 June 1975. Mice were allowed to populate all grids until late December 1975. Four of the grids contained a centralized food (corn) depot while the other 4 contained equally spaced decentralized depots. Peak densities were reached in all populations by 1 November 1975. Populations in centralized grids reached a mean peak density of -20 animals per grid while the mean peak density in the decentralized grid populations was --30 animals per grid. Decreases in the following population pa- rameters were found in both grid types with increased population densities: reproduction, juvenile mortality, population growth rates, and average cohort weights at first month of trapping. The d d and Y Y in decentralized grids exhibited greater survivorship than did d d and Y Y in centralized grids, respectively. Corn consumption was greatest in all grids after mid-October. Animals in the decentralized grids utilized a greater percent of corn to fulfill their energetic requirements than did animals in the centralized grids throughout the study. In the decentralized grids d d and Y Y were found to have similar assimilation efficiencies no matter where they were trapped in the grids. How- ever, animals from peripheral areas in centralized grids exhibited significantly lower assimilation efficiencies than did animals from food-depot locations. Uneven partitioning of food resources, com- pounded by high population density, has a greater depressing effect on population growth and struc- ture than does high density alone.

Population Dynamics of the Big Brown Bat (Eptesicus fuscus) in Southwestern Ohio

Population dynamics of the big brown bat ( Eptesicus fuscus ) were studied for four years (1969–1972) in southwestern Ohio. Data were collected from 10,761 banded bats located in 81 summer nursery colonies and five winter hibernacula. Of 4506 immature big brown bats captured during the study period, 2223 (49.3 percent) were females. Contrary to previous studies, adult females outnumbered males in three of five winter hibernacul. Tooth wear of known age bats predicted population age class structure, but was a poor indicator of a specific age of a given individual. Survivorship curves for female bats were constructed from the percentage of banded individuals which were recaptured in subsequent years within the nursery colonies. Annual female mortality rate values for two large bat populations were 68.1, 28.7, and 72.0 percent and 89.5, 30.0, and 42.9 percent, respectively. Big brown bats recaptured at distances greater than 8 kilometers (km) (5 miles, mi) from the home colony were found to move in a southerly direction. In two instances record natural movements of 250 km and 290 km (155 and 180 mi) were recorded for E. fuscus . Larger populations of Eptesicus were located in the unglaciated region of the study area. Efficiency of young production per adult female was found to decrease with a corresponding increase in nursery population size. Merits of this inverse correlation efficiency as a potential population regulatory mechanism are discussed.

Influence of Simulated Landscape Corridors on House Mouse (Mus musculus) Dispersal

The major objective of this study was to evaluate the influence of contrasting landscape corridors on population dispersal behavior of feral house mice (Mus musculus). Eight 0.1-ha enclosures were divided into two linear systems of four enclosures each. The two end enclosures of each system were planted in oats (Avena sativa). Two 1-m wide corridors connected the end enclosures. Corridors in one system consisted of strips of unmowed vegetation; corridors in the other system consisted of strips of unmowed vegetation plus a split-rail fence. Trials were conducted in early summer, late summer, autumn and winter. Significantly more mice dispersed in the corridors containing the split-rail fence during late summer and autumn, whereas equal numbers dispersed in both corridors in early summer and winter. Significantly more adult males dispersed than did adult females. Population density was not responsible for differences in dispersal rates observed between the two systems. Results suggest that both the vegetative and man-made corridor components influence the dispersal of small mammals within an agricultural landscape.

Effects of municipal sludge and fertilizer on heavy metal accumulation in earthworms

Abstract Comparisons were made of heavy metal concentrations of cadmium, copper, lead, and zinc in Lumbricus rubellus collected from a three-year-old field community in which replicate plots were treated five times annually for four years with either fertilizer, sewage sludge, or left untreated as controls. Concentrations of all four metals were significantly higher ( P ≦ 0·05) in the soil from sludge-treated plots than from fertilizer or control plots. Cadmium concentration was approximately nine times greater in earthworms from sludge plots than in those from control or fertilizer plots. Although amounts of copper ( x = 20·7 μg g −1 ) and lead (8·75 μg g −1 ) were also significantly higher in earthworm tissue from sludge-amended communities as compared to fertilizer or control treatments, concentration factors were relatively low, suggesting possible biological regulation of these metals. No significant differences were found between treatments for zinc concentrations in earthworm tissue. Lumbricus rubellus appears to be an ideal indicator species for investigating rates of heavy metal uptake within terrestrial ecosystems.