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Grassland birds have undergone widespread global population declines due to loss and degradation of native grasslands. Activities associated with non-renewable energy derived from oil and natural gas extraction have substantially increased on grasslands. The cumulative disturbance generated by natural gas development creates a network of non-linear (e.g., bare ground and exotic plant species) and linear (e.g., roads, trails, pipelines) features that may degrade habitat quality for grassland species. We quantified grassland songbird abundance in two areas of southwestern Saskatchewan, Canada, to determine whether variation in abundance 1) depended on the type and amount of disturbance at two spatial extents, and 2) was more affected by the cumulative impacts of natural gas development than any single type of disturbance. We found that specific types of disturbances impacted the abundance of most species to varying degrees. The cover of different types of linear disturbance had the strongest effect on the most species. Natural gas disturbance within 450 m of point counts was more influential than disturbance within 200 m for nearly all species in both areas. Only Savannah sparrow ( Passerculus sandwichensis ) abundance was most strongly influenced by the cumulative amount of disturbance with abundance decreasing with increased disturbance. Overall, we detected few consistent patterns among species, or within species between our two study areas. Our results indicated that the impact of natural gas infrastructure can extend beyond the local influences associated with well sites and that relatively small amounts of disturbance (<2%) may impact grassland songbird abundance. We recommend that researchers use caution when studying well-density effects or combining individual types of disturbance without understanding the separate effects each type of disturbance has on the species or community of interest. Not doing so may lead to investing resources into management practices that do not have the greatest possible benefit for grassland songbirds.

Aquatic invertebrates provide important ecosystem services, including decomposition and nutrient cycling, and provide nutrition for birds, fish, amphibians, and bats. Thus, the effects of agricultural land management practices on aquatic invertebrates are relevant to farmers, wildlife biologists, and policymakers. Here, we used data on aquatic invertebrates (159 taxa, 73 to species, 75 to genus/family) collected in 40 wetlands in the Canadian prairies to test for direct and indirect relationships among land management types (perennial cover, organic, minimum tillage, conventional), landscape structure (cropland and wetland cover within the surrounding landscape), and water quality (total nutrient levels, turbidity) on species richness of invertebrates using structural equation modelling. Additionally, we assessed variation in community composition within and among wetlands in different land use management types using a direct gradient analysis and variance partitioning. The direct effects of land management type were not supported but we found strong supportive evidence that effects of land management on richness were significantly mediated through cropland cover, nutrient levels, and turbidity. After controlling for these indirect effects, aquatic invertebrate richness decreased along a gradient from the lowest to the highest farming intensity, i.e., richness decreased from perennial cover sites to organic to minimum tillage to conventional sites. Support was also found for negative effects of nutrient levels and turbidity on richness. We did not find significant support for differences in gamma diversity or a simple test (homogeneity of multivariate dispersions) of differences in turnover among land management types; however, land management had a significant effect in distance-based redundancy analysis. Taken together, these results suggest that focusing conservation efforts on reducing cropland erosion and nutrient inputs to wetlands and creating more permanent cover may be effective strategies for conserving richness of aquatic invertebrates in agricultural landscapes in this region.

Mediterranean maquis vegetation is highly biodiverse, but widespread grazing poses a challenge for management and conservation. We sampled woody and herbaceous plants separately on a limestone mountain with strong mesic-xeric gradients in Tunisia’s Parc National de L’Ichkeul, assessed grazing pressure (on a scale of 1–3), and asked whether grazing had a significant effect on plant compositional abundance before and after controlling for environmental covariates. Sites on the more mesic lakeside face of the mountain were most compositionally unique, and forbs contributed most to the herbaceous beta-diversity on the mountain. We used variance partitioning to separate the collective and individual effects of the abiotic environment, grazing, human activity, and space on herbaceous and woody beta-diversity. However, the individual effect of grazing on overall plant community composition was confounded with space, due to the spatially autocorrelated grazing pressure on the mountain. Importantly, we found that herbaceous and woody communities responded differently to increasing levels of grazing intensity: herbaceous beta-diversity was highest between sites with no grazing pressure, while woody beta-diversity peaked under light grazing. Herbaceous community composition was sensitive to any intensity of grazing pressure, and biotic homogenization occured under moderate-to-high grazing pressure. On the other hand, woody community composition remained relatively similar under no to light grazing pressure, but differed under moderate-to-heavy grazing. Using a one-way permutational analysis of variance analysis, we showed that grazing had a significant effect when controlling for abiotic and spatial covariates. Our findings offer insight into the effects of grazing on maquis vegetation at Jebel Ichkeul, acting as a microcosm of similar conservation and management issues elsewhere in the Mediterranean. We suggest that a combination of monitoring and carefully controlled grazing may enhance plant diversity and maintain the region’s biodiverse maquis vegetation, potentially maintaining a key climate refugium for vulnerable endemic species. Importantly, our study provides a useful baseline of the plant assemblages at Jebel Ichkeul with which to compare future vegetation changes.

Invasion by generalist tree species can cause biotic homogenization, and such community impoverishment is likely more important in rare forest types. We quantified changes in tree diversity within Carolinian (range in Central Hardwood Forest), central (range in Central Hardwood Forest and Northern Hardwood‐Conifer Forest), and northern species [range reached Northern‐Conifer‐Hardwood/closed Boreal (spruce‐Fir) Forest] in an old forest tract in southern Canada at points surveyed 24 years apart. We asked: How did mature tree and sapling composition and abundance change for the three species’ groups? Did those changes lead to biotic homogenization? Can species’ changes be explained by community traits? We tested for differences in temporal and spatial tree β‐diversity, as well as forest composition and structure, using univariate/multivariate analyses and a community trait‐based approach to identify drivers of change. Major increases occurred in abundance for mature Acer rubrum (northern), while other species decreased (Fraxinus americana, Populus grandidentata); declines were found in A. saccharinum (central) and Cornus florida (Carolinian). Species composition of saplings, but not mature trees, changed due to replacement; no evidence for biotic homogenization existed in either cohort. As a group, northern mature tree species increased significantly, while central species decreased; saplings of pooled Carolinian species also declined. Shade tolerance in mature trees increased, reflecting successional changes, while drought tolerance decreased, perhaps due to changing temperatures, altered precipitation or ground water levels. Saplings showed declines in all traits, probably because of compositional change. Our results demonstrated that saplings can more closely reflect change in forest dynamics than mature trees, especially over short time periods. Based on sapling trends, this remnant could ultimately transition to a mesophytic hardwood stand dominated by A. rubrum and other shade‐tolerant species, creating a more homogeneous forest. While encouraging regeneration for Carolinian and central tree species could ensure high levels of diversity are conserved in the future, it is important to balance this with the primary management goal of maintaining the forest's old‐growth characteristics. Our results highlight the importance of monitoring tree β‐diversity in long‐term forest plots to examine changes in homogenization, species composition, and functional traits which can lead to management and conservation outcomes. We demonstrated compositional and functional changes in an old growth forest driven mainly by invasion of red maple. Although we did not observe biotic homogenization, these changes indicated potential for future homogenization of this remnant and those of surrounding forests. This raises important conservation issues: whether or not to manage this and other forests to maintain tree biodiversity.

Modelling the distribution and abundance of species at risk is extremely important for their conservation and management. We used ecological niche models (ENMs) to predict the occurrence of western rattlesnakes (Crotalus oreganus) in British Columbia (BC), Canada. We applied this to existing population estimates to support a threshold of occurrence for management and conservation. We also identified predictors influencing rattlesnake distribution and abundance in this region. Using a Geographic Information Systems platform, we incorporated ENMs, capture–mark–recapture (CMR) and radio-telemetry results, province-wide observations, Landsat imagery and provincial databases for agricultural land use to produce quantitative, spatially explicit, population estimates across BC. Using available western rattlesnake habitat estimated at 183.9 km2 and averaging estimates calculated from densities in three study populations, we generated a mean adult population size of 9722 (±SD 3009; 0.8 relative index of occurrence [RIO] threshold). Only a small area (21.6 km2) of suitable land cover was located within protected areas, potentially protecting an estimated 1144 (±354) adults. Most suitable land cover was within 500 m of roads (170.6 km2), representing potential habitat being used by an estimated 9017 (±2791) adults. At the threshold RIO value chosen (0.8), only a very small area of farmland provided suitable land cover. Our results highlight the possibility of high mortality rates for western rattlesnakes near roads and the fact that protected areas do not provide sufficient coverage to conserve the population. Given that this species has relatively low mobility and high site fidelity to home ranges, our population estimate for BC provides a useful reference for the northern part of the species’ range. It also fulfills a need to estimate population size within political jurisdictions where conservation management decisions are made, as well as presenting a method that can be applied to other parts of the range, including the southern United States. Our study provides an important benchmark for future monitoring of western rattlesnakes in BC using a repeatable and transparent approach. Similar applications can be extrapolated and applied for other threatened species to identify and quantify population distributions and threats, further supporting conservation prioritization tools to be used to maximize the effectiveness of conservation strategies under financial constraints.

Intraspecific competition is believed to play a pivotal role in shaping the structure and resource use of migrant and resident bird communities. We compared seasonal movements and apparent survival of patagially-markcd and radio-tagged individuals of a Neotropical subspecies of Turkey Vulture (Cathartes aura ruficollis) in central Venezuela in relation to the presence and absence of a larger, dominant, northern subspecies, C. a. meridionalis. We found that the ruficollis population was partially migratory during the periods when migrants arrived and departed. Tagged individuals used areas with higher and lower proportional forest and semi-open vegetation types, respectively, during the dry season than wet season months to avoid competition with migrants. Moreover, apparent survival of ruficollis was lower during sympatry than allopatry. Our study provided evidence that C. a. meridionalis competed with C. a. ruficollis during their tropical residence period, supporting the hypothesis that intraspecific competition contributes to niche separation between these subspecies.

We examined the possibility that granular insecticides, used intensively in the Canadian prairies to control flea beetles (Phyllotreta sp.) in canola (Brassica napus and B. napa), could contribute to bird population declines. A retrospective analysis (1971–96) was done to investigate relationships between counts of 29 bird species made on Breeding Bird Survey (BBS) routes with a spatially explicit granular use index (derived from surveys made in 1980–85) and an index of land use change (derived from Principal Components Analysis of agricultural statistics) for 30 Census Agricultural Regions (CARs). Controlling for spatial location and the land use change index, abundance of American robin (Turdus migratorius), horned lark (Eremophila alpestris), house sparrow (Passer domesticus), mourning dove (Zenaida macroura), and western meadowlark (Sturnella neglecta) was negatively correlated with insecticide use; only two species showed evidence of a positive correlation. At a shorter time scale, for which we had direct estimates of pesticide use (1980–85), we also found evidence that the black-billed magpie (Pica pica), European starling (Sturnus vulgaris), and killdeer (Charadrius vociferus) were less abundant in areas where granular insecticide use was high. Population trends (% annual change between 1971–96) were negatively correlated with the granular index for horned lark, house sparrow, and western meadowlark. Although correlational only, our results suggest that granular insecticides may be an important factor influencing population changes in some bird species in prairie farmland.

Intraspecific competition is believed to play a pivotal role in shaping the structure and resource use of migrant and resident bird communities. We compared seasonal movements and apparent survival of patagially-marked and radio-tagged individuals of a Neotropical subspecies of Turkey Vulture (Cathartes aura ruficollis) in central Venezuela in relation to the presence and absence of a larger, dominant, northern subspecies, C. a. meridionalis. We found that the ruficollis population was partially migratory during the periods when migrants arrived and departed. Tagged individuals used areas with higher and lower proportional forest and semi-open vegetation types, respectively, during the dry season than wet season months to avoid competition with migrants. Moreover, apparent survival of ruficollis was lower during sympatry than allopatry. Our study provided evidence that C. a. meridionalis competed with C. a. ruficollis during their tropical residence period, supporting the hypothesis that intraspecific competition contributes to niche separation between these subspecies. La competencia intraespecífica juega un papel fundamental en la estructura y uso de recursos de las comunidades de aves migratorias y residentes. Comparamos los movimientos estacionales y la sobrevivencia aparente de la cataneja cabeza roja neotropical (Cathartes aura ruficollis) marcada patagialmente y con radiotransmisores en el centro de Venezuela con relación a la presencia y ausencia de una subespecie boreal más grande y dominante, C. a. meridionalis. Encontramos que algunos individuos de ruficollis eran migrantes parciales durante la estación seca, utilizaban áreas con mayor y menor proporción de vegetación boscosa y ambientes semiabiertos, respectivamente, durante la estación seca en comparación con los meses de la estación húmeda para evitar la competencia con los migratorios boreales, y que la sobrevivencia aparente de ruficollis fue más baja durante simpatría que en alopatría. Nuestro estudio proporcionó evidencia de que C. a. meridionalis podría competir con C. a. ruficollis durante su período de residencia tropical, lo que respalda la hipótesis de que la competencia intraespecífica podría contribuir a la separación de nichos entre estas subespecies. Palabras clave: cobertura del suelo, competencia, Neotrópico, reparto de recursos, Venezuela.

Mediterranean vegetation is characterized by high biodiversity and conservation value and grazing is controversial. We sampled woody and herbaceous plants on a limestone mountain with strong mesic-xeric gradients, ranked grazing pressure (on a scale of 1-4) and asked whether grazing had a significant effect on plant compositional abundance before and after controlling for environmental covariates. For woody species the shift in means among grazing classes was greater than for herbaceous species according to distance-based redundancy analysis (dbRDA). For herbaceous species differences in multivariate dispersion were greater among grazing classes. Both groups showed significant differences among grazing classes in multivariate location (permutational multivariate ANOVA), even after controlling for aspect. After taking into account biophysical covariates, grazing was not significant and the variation unique to grazing was small. According to best models in dbRDA, grazing was significant in two models for woody species, and all models for herbaceous species. For woody species, spatial variables were most important and confounded with grazing while for herbs, altitude, distance to road, slope, rock outcropping were important. Significant effects of grazing were found for forbs, Poaceae, and Geophytes but not woody and herbaceous legumes. We found a negative relationship between grazing intensity and beta diversity for herbs overall and especially Poaceae, but moderate grazing resulted in higher beta diversity for Geophytes and herbaceous legumes. Jebel Ichkeul provides a microcosm of similar conservation and management issues elsewhere in the Mediterranean. Carefully controlled grazing may enhance plant diversity and maintain the characteristics of maquis vegetation.