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Refuge Habitats (refuge + habitat)
Selected AbstractsRefuge habitats modify impact of insecticide disturbance on carabid beetle communitiesJOURNAL OF APPLIED ECOLOGY, Issue 2 2001Jana C. Lee Summary 1Carabid beetles are polyphagous predators that can act as biological control agents of insect pests and weeds. While current agricultural practices often create a harsh environment, habitat management such as the establishment of within-field refuges has been proposed to enhance carabid beetle abundance and impact. We examined the joint effects of refuge habitats and insecticide application on carabid activity density (parameter of population density and relative activity) and species composition in a cornfield. 2Our 2-year study comprised four treatments: (i) ,refuge/,insecticide; (ii) +refuge/,insecticide; (iii) ,refuge/+insecticide; (iv) +refuge/+insecticide. Refuge strips consisted of grasses, legumes and perennial flowering plants. ,,Refuge' strips were planted with corn and not treated with insecticide. 3Before planting and insecticide application, carabid activity density in the crop areas was similar across all treatments. Insecticide application immediately reduced carabid activity density and altered community composition in the crop area. 4Refuge strips had significantly higher activity density of beetles than ,refuge strips before planting and during the summer. 5During summer, as new carabids emerged and insecticide toxicity declined, the presence of refuge strips influenced carabids in the adjacent crop area. Carabid activity density within crop areas previously treated with insecticide was significantly higher when adjacent to refuge strips. Also, carabid communities within insecticide-treated crop areas were affected by the presence or absence of a refuge strip. 6The presence of refuge strips did not consistently augment carabid numbers in crop areas where insecticide was not applied. One explanation may be that insecticides decreased the quality of crop habitat to carabids by depletion of prey and direct mortality. However, subsequent rebounds in prey density and the absence of competing predators may make these areas relatively more attractive than unperturbed crop habitats to carabid colonization from refuges. 7This study demonstrates that refuges may buffer the negative consequences of insecticide application on carabids in adjacent fields. Diversifying agro-ecosystems with refuge habitats may be a viable strategy for maintaining carabid populations in disturbed agricultural landscapes to keep pests below outbreak levels. [source] Experimental manipulation reveals the importance of refuge habitat temperature selected by lizardsAUSTRAL ECOLOGY, Issue 3 2010MICHA ANDERSSON Abstract Refuges provide shelter from predators, and protection from exposure to the elements, as well as other fitness benefits to animals that use them. In ectotherms, thermal benefits may be a critical aspect of refuges. We investigated microhabitat characteristics of refuges selected by a heliothermic scincid lizard, Carlia rubrigularis, which uses rainforest edges as habitat. We approached lizards in the field, simulating a predator attack, and quantified the refuge type used, and effect of environmental temperatures (air temperature, substrate temperature and refuge substrate temperature) on the amount of time skinks remained in refuges after hiding (emergence time). In respone to our approach, lizards were most likely to flee into leaf litter, rather than into rocks or woody debris, and emergence time was dependent on refuge substrate temperature, and on refuge substrate temperature relative to substrate temperature outside the refuge. Lizards remained for longer periods in warmer refuges, and in refuges that were similar in temperature to outside. We examined lizard refuge choice in response to temperature and substrate type in large, semi-natural outdoor enclosures. We experimentally manipulated refuge habitat temperature available to lizards, and offered them equal areas of leaf litter, woody debris and rocks. When refuge habitat temperature was unmanipulated, lizards (85%) preferred leaf litter, as they did in the field. However, when we experimentally manipulated the temperature of the leaf litter by shading, most skinks (75%) changed their preferred refuge habitat from leaf litter to woody debris or rocks. These results suggest that temperature is a critical determinant of refuge habitat choice for these diurnal ectotherms, both when fleeing from predators and when selecting daytime retreats. [source] Factors affecting habitat selection by a small spawning charr population, bull trout, Salvelinus confluentus: implications for recovery of an endangered speciesFISHERIES MANAGEMENT & ECOLOGY, Issue 1 2004R. C. Wissmar Abstract Bull trout, Salvelinus confluentus (Suckley), populations are declining in many streams of North America and are listed under the Endangered Species Act in the United States. Many small populations are isolated in fragmented habitats where spawning conditions and success are not well understood. Factors affecting habitats selected for redds by spawning bull trout and redd habitat characteristics within Gold Creek, a headwater stream in the Yakima River within the Columbia River basin, Washington State, USA, were evaluated. Most spawning (>80% of the redds) occurred in upstream habitats after dewatering of downstream channels isolated fish. Habitats were selected or avoided in proportions different to their availability. For example, most bull trout selected pools and glides and avoided riffles despite the latter being more readily available. Although preferences suggest influences of prolonged fish entrapment, site fidelity could be important. A habitat with redds commonly contained abundant cover, gravel substratum and higher stream flows. The major factors influencing habitat selection by spawning fish and their persistence in streams of the Yakima and Columbia River regions include entrapment of fish by dewatering of channels and geographical isolation by dams. The goal of the US Government's recovery plan is ,to ensure the long-term persistence of self-sustaining bull trout populations'. Recovery plans linked to provisions for protecting and conserving bull trout populations and their habitats were recommended. Landscape approaches are needed that provide networks of refuge habitats and greater connectivity between populations. Concurrent recovery efforts are encouraged to focus on protecting small populations and minimizing dangers of hybridization. [source] Day,night changes in the spatial distribution and habitat preferences of freshwater shrimps, Gammarus pulex, in a stony streamFRESHWATER BIOLOGY, Issue 4 2005J. M. ELLIOTT Summary 1. As many invertebrates are nocturnal, their spatial distribution and habitat preferences may change from day to night. Both aspects are examined for Gammarus pulex by testing the hypotheses: (i) a power function was a suitable model for the spatial distribution of the shrimps in both day and night; (ii) diurnal and nocturnal spatial distributions were significantly different; (iii) diurnal and nocturnal habitat preferences were significantly different. Five different life-stages were treated separately. To ensure that the conclusions were consistent, large samples were taken near midday and midnight in April, June and November over 4 years at two sites about 3 km apart in a stony stream: downstream (n = 30) and upstream (n = 50). 2. The first and second hypotheses were supported at both sites. A power function, relating spatial variance (s2) to mean (m), was an excellent fit in all analyses (P < 0.001, r2 > 0.91), i.e. the spatial variance was density-dependent. All five life-stages were aggregated in the day. At night, the degree of aggregation increased for juveniles at higher densities but decreased for juveniles at lower densities, increased for immature females and males, but decreased slightly for mature females and especially mature males, the latter being close to a random distribution. There were no significant differences between sites, in spite of the lower numbers at the downstream site. 3. The third hypothesis was tested at only the upstream site and supported by comparisons between shrimp densities and 13 physical variables (distance from bank, water depth, water velocity, ten particle size-classes), and three non-physical variables (dry weights of bryophytes, leaf material, organic detritus). During the day, densities were strongly related to particle sizes with the following preferences: 0.5,8 mm for juveniles, 8,256 mm for the other life-stages with a weaker relationship for males. There were no significant positive relationships with the other variables, apart from bryophytes for immature shrimps and adults. At night, densities were unrelated to particle size; juveniles and immature shrimps preferred low water velocities near the banks, often where leaf material and organic detritus accumulated, females often preferred medium water velocities slightly away from the banks, and males showed no habitat preferences. 4. Day samples do not provide a complete picture of habitat preferences and probably identify refuge habitats. Day,night changes in spatial distribution and habitat preferences are an essential part of the behavioural dynamics of the shrimps and should be investigated in other species. [source] Spatial relationships between intensive land cover and residual plant species diversity in temperate farmed landscapesJOURNAL OF APPLIED ECOLOGY, Issue 6 2006SIMON M. SMART Summary 1In temperate farmed landscapes conservation policies increasingly emphasize large-scale reductions in land-use intensity. Yet despite a managed reversion to more favourable abiotic conditions, depleted regional species pools may prevent the re-assembly of target communities. 2Using national-scale survey data recorded across Great Britain in 1998, we investigated the extent to which grassland indicator plant species persisted on potential refuge habitats across a spatial gradient of intensive land cover in lowland 1-km squares. These habitats comprised road verges, field boundaries, watercourse banks and small biotope fragments. Intensive land cover comprised built land, arable and improved grassland. 3The rate of reduction in indicator species richness across the intensive land cover gradient was significantly lower in all potential refuge features than in surrounding fields and larger areas of habitat. 4The best refuge locations were watercourse banks and small biotopes. In both cases, indicator species richness was higher than adjacent fields at the lowest intensive land cover and stayed higher as intensive land cover increased. 5However, as intensive land cover increased, plant traits associated with higher nutrient availability were more prominently represented among indicator species. 6Although richer assemblages of indicator species persisted on refuge features, population sizes are likely to be small, because of species,area effects, and also vulnerable to nutrient surpluses and reduced or inappropriate disturbance. 7Synthesis and applications. Across the British lowlands, linear landscape features and small habitat fragments can provide limited safe havens for unimproved grassland plant species. However, the identity of refuge features and their species richness and composition are likely to vary with local conditions. Three activities are therefore paramount in assessing their role in larger scale extensification schemes: (i) development of rapid ways of assessing the plant diversity and distribution of refuge features in local areas; (ii) quantification of the risks posed to the viability of residual source populations through implementation of different options for incorporating them into extensification schemes; (iii) maximization of scheme performance by targeting landscapes with sufficient residual diversity to enable increases in population size of the target species in the medium term. [source] Refuge habitats modify impact of insecticide disturbance on carabid beetle communitiesJOURNAL OF APPLIED ECOLOGY, Issue 2 2001Jana C. Lee Summary 1Carabid beetles are polyphagous predators that can act as biological control agents of insect pests and weeds. While current agricultural practices often create a harsh environment, habitat management such as the establishment of within-field refuges has been proposed to enhance carabid beetle abundance and impact. We examined the joint effects of refuge habitats and insecticide application on carabid activity density (parameter of population density and relative activity) and species composition in a cornfield. 2Our 2-year study comprised four treatments: (i) ,refuge/,insecticide; (ii) +refuge/,insecticide; (iii) ,refuge/+insecticide; (iv) +refuge/+insecticide. Refuge strips consisted of grasses, legumes and perennial flowering plants. ,,Refuge' strips were planted with corn and not treated with insecticide. 3Before planting and insecticide application, carabid activity density in the crop areas was similar across all treatments. Insecticide application immediately reduced carabid activity density and altered community composition in the crop area. 4Refuge strips had significantly higher activity density of beetles than ,refuge strips before planting and during the summer. 5During summer, as new carabids emerged and insecticide toxicity declined, the presence of refuge strips influenced carabids in the adjacent crop area. Carabid activity density within crop areas previously treated with insecticide was significantly higher when adjacent to refuge strips. Also, carabid communities within insecticide-treated crop areas were affected by the presence or absence of a refuge strip. 6The presence of refuge strips did not consistently augment carabid numbers in crop areas where insecticide was not applied. One explanation may be that insecticides decreased the quality of crop habitat to carabids by depletion of prey and direct mortality. However, subsequent rebounds in prey density and the absence of competing predators may make these areas relatively more attractive than unperturbed crop habitats to carabid colonization from refuges. 7This study demonstrates that refuges may buffer the negative consequences of insecticide application on carabids in adjacent fields. Diversifying agro-ecosystems with refuge habitats may be a viable strategy for maintaining carabid populations in disturbed agricultural landscapes to keep pests below outbreak levels. [source] The role of spatio-temporal heterogeneity in the establishment and maintenance of Suaeda maritima in salt marshesJOURNAL OF VEGETATION SCIENCE, Issue 1 2002Marc Tessier Tutin et al. (1964,1980) Abstract. The effects of disturbance and microtopography on the organization and dynamics of plant communities were studied in a European salt marsh located in the Bay of Mont St. Michel, France. The existence of seed trapping mechanisms was also tested. The study took place in the lower and middle marsh plant communities dominated by the perennials Puccinellia maritima and Halimione portulacoides, respectively and associated with the annual Suaeda maritima. Three treatments were used in series of plots placed in each community: (1) vegetation removal and root destruction to a depth of 10 cm and refilling, (2) non-remnant herbicide treatment without vegetation removal and (3) creation of depressions (20 cm deep). These treatments were compared with adjacent control plots. The first year of the experiment showed that the perennials facilitated the establishment of Suaeda by trapping its seeds. Estimation of cover, density and biomass over 5 yr following the disturbances showed that in the first 2 yr Suaeda dominated the disturbed plots. Thereafter Suaeda was gradually eliminated by competitive exclusion after ca. 3 yr in the zone originally dominated by Puccinellia maritima and after 4 yr in the zone occupied by Halimione portulacoides. Depressions constituted refuge habitats for Suaeda by limiting competition with the perennials but also led to a high risk of mortality with temporal fluctuations in density. Despite a period of investigation limited to 5 yr, our study demonstrated that natural disturbances of various types occurred and influenced the dynamics of Suaeda, Halimione and Puccinellia. We deduced that natural disturbances and microtopography are responsible for the maintenance of the habitat in a state of non-equilibrium by favouring the establishment of both spatial and temporal environmental heterogeneity. These conditions appear to be particularly favourable for the maintenance of annual species such as Suaeda maritima. [source] | |||||||||||||