No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Novel landscape elements within natural gas fields increase densities but not fitness of an important songbird nest predator
... The bird species with the greatest number of tests was the great-er sage-grouse (Centrocercus urophasianus) with 52 tests X(N = 11 studies), followed by the chestnut-collared longspur (Calcarius ornatus), with 51 tests from eight studies. Of the mammal papers, the majority focused on ungulates (N = 32 tests from 14 studies), with three on medium-sized mammals (small canids and mustelids) [17][18][19], two on the deer mouse [17,20], one on least chipmunks (Tamias minimus) [21], one on pygmy rabbits (Brachylagus idahoensis) [22•], and one on a large carnivore (grizzly bear, Ursus arctos) [23]. The two mammalian species that received the most study were pronghorn (Antilocapra americana; N = 19 tests from six studies) and mule deer (Odocoileus hemionus; N = 13 tests from eight studies). ...
... Understanding the processes underlying observed patterns holds particular value for formulating effective mitigation measures. As a case study, sagebrush songbirds nesting within natural gas fields experienced higher nest predation rates, which was associated with increased densities of synanthropic rodents attracted to the reseeded areas around well pads and pipelines [17,20,21]. Reproductive success of songbirds would therefore likely benefit from the reduction of initially disturbed soils and/or reclamation practices that more closely mimic initial conditions. ...
... Negative responses, however, were universally detected (albeit with relatively low frequency) across taxa, locations, and development type, and with respect to different response types and development indices (Fig. 1). Moreover, positive responses to development by some species can have negative downstream consequences for other species, such as the case of increased rodent abundance and the nest predation rates of sagebrush songbirds [17,20,21]. ...
Purpose of Review
Anthropogenic activities can lead to the loss, fragmentation, and alteration of wildlife habitats. I reviewed the recent literature (2014–2019) focused on the responses of avian, mammalian, and herpetofaunal species to oil and natural gas development, a widespread and still-expanding land use worldwide. My primary goals were to identify any generalities in species’ responses to development and summarize remaining gaps in knowledge. To do so, I evaluated the directionality of a wide variety of responses in relation to taxon, location, development type, development metric, habitat type, and spatiotemporal aspects.
Recent Findings
Studies ( n = 70) were restricted to the USA and Canada, and taxonomically biased towards birds and mammals. Longer studies, but not those incorporating multiple spatial scales, were more likely to detect significant responses. Negative responses of all types were present in relatively low frequencies across all taxa, locations, development types, and development metrics but were context-dependent. The directionality of responses by the same species often varied across studies or development metrics.
Summary
The state of knowledge about wildlife responses to oil and natural gas development has developed considerably, though many biases and gaps remain. Studies outside of North America and that focus on herpetofauna are lacking. Tests of mechanistic hypotheses for effects, long-term studies, assessment of response thresholds, and experimental designs that isolate the effects of different stimuli associated with development, remain critical. Moreover, tests of the efficacy of habitat mitigation efforts have been rare. Finally, investigations of the demographic effects of development across the full annual cycle were absent for non-game species and are critical for the estimation of population-level effects.
... We defined surface disturbance as any area that had been converted from sagebrush habitat as a result of development activities, including roads, pipelines, well pads, and reclaimed areas (in which mature sagebrush habitat had been removed during well, road, or pipeline construction and re-seeded). Whereas areas where habitat has been disturbed by energy development activities may represent habitat loss for sagebrushobligate songbirds (which breed and forage exclusively in the shrub layer), these areas represent altered, but still useable habitat for rodents (Sanders and Chalfoun 2018). ...
... Indeed, habitat modifications that lead to increased edge habitat and food resources, such as urbanization, agriculture, and energy development, tend to have the most positive effects on synanthropic species, such as deer mice and ground squirrels (Eagan et al. 2011). See Sanders and Chalfoun (2018) for further investigation into this potential mechanism. Because we could not estimate emigration and immigration rates for deer mice, our estimates of apparent survival could be confounded (Williams et al. 2002). ...
... Given our results, apex predators living near energy development do not need to be controlled to protect declining songbird populations (sensu Dinkins et al. 2016)-rather, apex predators may actually be helping to regulate rodents on natural gas fields. Moreover, our elimination of the mesopredator release hypothesis is important for strong inference and clears a path for the assessment of alternate explanations for observed patterns in mesopredator density and altered species interactions with energy extraction (Sanders and Chalfoun 2018). Effective strategies for the mitigation of negative effects of human-induced habitat change on species of concern rely on such mechanistic understanding. ...
Anthropogenic activities are changing landscapes and the context in which predator–prey dynamics evolved, thereby altering key ecological processes and community structure. Yet, the specific mechanisms underlying such changes are rarely understood. We tested whether a mesopredator release explained increased rodent density and concomitant predation of songbird nests near natural gas development. From 2015 to 2016, we surveyed apex predators (coyotes, badgers, raptors, and corvids) and measured apparent survival and perceived predation risk of deer mice (Peromyscus maniculatus; a primary nest predator), at 12 plots spanning a gradient of surface disturbance caused by energy development in Wyoming, USA. Additionally, we measured densities of three nest predators: deer mice, least chipmunks (Tamias minimus), and thirteen‐lined ground squirrels (Ictidomys tridecemlineatus). Contrary to the mesopredator release hypothesis, counts of apex predators and perceived predation risk of deer mice increased with surface disturbance from energy development, whereas apparent survival of mice decreased. Densities of mice and ground squirrels, however, increased with surface disturbance, despite increased predation pressure. We therefore rejected the mesopredator release hypothesis as a potential mechanism underlying altered trophic dynamics near energy development. Our results suggest that apex predator control measures would not benefit declining songbirds on natural gas fields. Rather, apex predator abundance may be regulated from the bottom‐up by rodents in this system. Our results corroborate a pattern showing weakened effects of mesopredator release in habitats modified by humans. Understanding how predator–prey dynamics may be altered in novel environments requires an understanding of how predators and prey alike respond to habitat change under different contexts.
... Plots were paired and separated by ≥ 650 m within pairs and ≥ 800 m among pairs to limit deer mouse movement between plots and pairs and ensure spatial independence. These distances were informed by the extent of movements documented by powder tracking experiments of deer mice during a previous, nearby study (Sanders and Chalfoun 2018). One plot within each pair was randomly selected as the experimental plot, with the other serving as a reference. ...
... In the three reference plots, trapping 8 grids consisted of 49 trap locations arranged in a 7 x 7 array with 40 meter spacing between traps. The spacing for our reference plot trapping grids were informed by previous research in the study area (Sanders and Chalfoun 2018) and were sufficient to evaluate the density of deer mice within a plot. Both trapping grids consisted of Sherman live traps, baited with a mixture of peanut butter and oats. ...
Many species of wildlife go through portions of their life history where they are
especially vulnerable to the impacts of biotic factors, such as predation, or numerous
abiotic factors, such as weather events. The early life history of many bird species is
characterized by a particularly vulnerable life stage in which they are immobile and bound
to their nest location. Any selective pressures occurring during this period modulate avian
biology to a large extent. We used a multifaceted approach (i.e., a controlled field
experiment and an empirical study) in Wyoming, USA to address the following questions
related to sagebrush songbird (Brewer’s Sparrow, Sagebrush Sparrow, Sage Thrasher)
reproductive success: Chapter 1) Does nest predation by a synanthropic nest predator
constitute additive or compensatory nest mortality? Chapter 2) How does an important
phenotypic metric (mass) vary among nestlings in larger brood sizes and among three
songbird species? We found little evidence that nest predation by deer mice on songbird
nests operated in an additive manner. The year in which we conducted our experimental
removal, however, had very high rates of nest survival. In our second study, intrabrood
mass variation between the largest and smallest siblings of a brood differed by species
(Brewer’s sparrow, Vesper Sparrow, Sage Thrasher) but was overall more extreme in
larger broods. How size differences among siblings specifically manifested, however,
differed by species. Our findings help characterize the survival pressures nestlings
experience early in life and provide additional information regarding this critical life stage.
... The specific mechanisms that drive impacts of energy development (i.e., increased predation risk) on songbird nest survival are not well understood (but see Sanders and Chalfoun 2019). Impacts of energy development on songbird nest survival have been attributed to the physical footprint (hereafter footprint) of development (native habitat removal, fragmentation, and anthropogenic edge; Hethcoat and Chalfoun 2015a, Bernath-Plaisted and Koper 2016, Sanders and Chalfoun 2018 and to specific energy infrastructure features such as power lines (DeGregorio et al. 2014). ...
... Within these scales we used zonal statistics to calculate vegetation covariates including mean Normalized Difference Vegetation Index (NDVI), mean forb and grass understory cover, percent big sagebrush canopy cover, average sagebrush height (cm), and the standard deviation of sagebrush height (Table 1; Xian et al. 2015, Robinson et al. 2017, Jones et al. 2018, Yang et al. 2018. NDVI is as a measure of primary productivity (Robinson et al. 2017 Greater grass and forb cover and higher NDVI values can be positively associated with the abundance of deer mice (Peromyscus maniculatus), which are known to depredate Brewer's Sparrow nests (Hanser et al. 2011, Heathcoat and Chalfoun 2015a, Sanders and Chalfoun 2018. We used 30-m resolution NDVI products generated every 16 days (Robinson et al. 2017) to calculate Mean NDVI layers. ...
Songbird communities that rely on sagebrush habitat for breeding are experiencing steep population declines, while a large amount of the sagebrush ecosystem continues to be impacted by energy development. Reclamation is increasingly emphasized as a means of mitigating impacts on species that have been affected by oil and gas development; however, the response of sagebrush species to reclamation has largely been untested. We used nest survival of the Brewer's Sparrow (Spizella breweri breweri) as an indicator of fitness responses to short-term reclamation in sagebrush habitat. We assessed oil and gas reclamation ~5 years after reclamation, but sagebrush reestablishment is a slow process; thus, the legacy of these disturbances (i.e., disturbance scars) will likely remain for decades. We compared Brewer's Sparrow nest survival across a gradient of oil and gas development from undisturbed and active development to areas that had undergone oil and gas reclamation. Nest survival was assessed at multiple scales from microhabitat to landscape. The distribution of nest sites in the active and reclamation areas suggested local avoidance of disturbance, both active and reclamation disturbance, when establishing nesting territories. We found that reclamation benefited nest survival at a local-scale when disturbance exposure exceeded 15%. Our findings demonstrated scale-dependent nest survival relationships. Across microhabitat and landscape scales, sagebrush canopy cover and composition were important to Brewer's Sparrow nest survival. Combined, these finding emphasize the importance of avoiding the removal of sagebrush habitat whenever possible and expediting sagebrush reestablishment in reclamation areas to maintain high quality sagebrush habitat for breeding songbird populations.
... Energy development areas have the potential to become equal preference ecological traps for species in the sagebrush ecosystem (Hethcoat and Chalfoun, 2015a). Specifically, increased densities of Brewer's sparrow, vesper sparrow, and western meadowlark nest predators (e.g., rodents, corvids, American badgers; Taxidea taxus) are associated with energy development areas in many grassland and shrubland ecosystems (Grant et al., 2006, Davis and Lanyon, 2008, Coates et al., 2014, Hethcoat and Chalfoun, 2015b, Ludlow et al., 2015, Bernath-Plaisted et al., 2017, Sanders and Chalfoun, 2018. For example, vesper sparrow nest density increased with proximity to infrastructure, leading to decreased nest success, likely due to an increase in nest predators near development areas (Bernath-Plaisted and Koper, 2016). ...
Reclamation projects encompassing more than several square kilometers (hereafter; landscape-scale) are a recommended strategy to mitigate the impacts of energy development on wildlife. However, the response of wildlife to landscape-scale reclamation remains largely undocumented. Oil and gas developments have contributed substantially to the loss and degradation of sagebrush ecosystems in North America. Management agencies are prioritizing habitat reclamation to mitigate habitat loss with an assumed benefit to wildlife, including songbirds. To determine the influence of landscape-scale habitat reclamation on songbirds, we measured avian species abundance and community composition in sagebrush habitats across a gradient of energy development: 1) active oil and gas, 2) landscape-scale reclamation, and 3) undisturbed sagebrush, in northeastern Wyoming, USA (2016–2018). We modeled the influence of treatment (active, reclaimed, and control), and key habitat variables on songbird abundance using a Bayesian hierarchical approach. We also assessed differences in community composition across treatments using the rarity-weighted richness estimate and the Jaccard Similarity Index. Reclamation efforts had a measurable influence on some species abundance. Human-commensal species increased in abundance with increasing disturbance, which may have increased species richness and rarity in our active and reclaimed sites. The community composition in reclaimed areas more closely resembled undeveloped habitat (control), than active development areas. Terrain roughness was the most consistently influential variable on abundance, and we recommend that this often overlooked habitat variable be included in future studies. The habitat variables that represent where we can most easily target reclamation efforts (e.g., herbaceous cover) had minimal influence on abundance.
Understanding species’ responses to temperature via behavior, and the factors affecting the extent of behavioral responses, is a critical and timely endeavor given the rapid pace at which the climate is changing. The young of altricial songbirds are particularly sensitive to temperature, and parents may modulate temperatures at nests via selection of nest sites, albeit to a largely unknown extent. We examined whether sagebrush-obligate songbirds, that reproduce within an open ecosystem with wide temperature fluctuations and span a range of body sizes, selected their nest sites on the basis of temperature. We further investigated whether nest predation risk and ambient conditions modulated temperature-based choices. We placed temperature loggers at nest sites and in unused but available nest niches and nest shrubs along a known predation-risk gradient and used nearby weather stations to determine ambient temperatures. The two smaller-bodied birds, Brewer’s Sparrow (Spizella breweri) and Sagebrush Sparrow (Artemisiospiza nevadensis), selected nest shrubs and niches that were warmer and less variable relative to unused sites whereas the larger bodied species, Sage Thrashers (Oreoscoptes montanus), did not. Brewer’s Sparrows and Sage Thrashers dampened selection for warmer nest sites when temperatures experienced during the nest-site prospecting period were warmer. None of the three species altered nest-site selection with respect to temperature in response to ambient temperature variability or our index of nest predation risk. The microhabitat characteristics that most influenced temperatures at nests varied across species. Our results suggest that songbirds can modulate temperatures at nests to some extent, and such responses can vary depending on the conditions experienced prior to nest initiation. Responses also varied across species, likely reflecting different physiological tolerances. The extent to which breeding birds will be able to continue to proximately influence temperature via nest-site choices likely will depend on the extent and rate of future climatic shifts.
Amphibians and reptiles are vertebrates that are often overlooked in assessments of the importance of sagebrush (Artemisia spp.) ecosystems for wildlife. Given their dependence on water, few amphibians are strongly associated with sagebrush habitats, although several use these uplands for foraging, shelter, or dispersal. Of the 60 amphibian species that are predicted to occur within the sagebrush biome, the Great Basin spadefoot (Spea intermontana) is probably the only species that occupies enough of the biome and lives predominantly in terrestrial habitats (mostly in burrows) to be considered sagebrush associated. Of the 116 reptiles that are predicted to occur within the sagebrush biome, about 5 lizards and 5 snakes were identified as both strongly associated with sagebrush habitats and occupied areas likely to be managed for sage-grouse (Centrocercus spp). However, this list could be lower or higher depending on the specific location within the biome, and there remains considerable uncertainty regarding potential threats to reptiles, as well as basic information on distribution and abundance of most reptile species.
Adaptive management and monitoring efforts focused on vegetation, habitat, and wildlife in the sagebrush (Artemisia spp.) biome help inform management of species and habitats, predict ecological responses to conservation practices, and adapt management to improve conservation outcomes. This chapter emphasizes the adaptive resource management framework with its four stages: (1) problem definition, (2) outcomes, (3) decision analysis, and (4) implementation and monitoring. Adaptive resource management is an evolving process involving a sequential cycle of learning (the accumulation of understanding over time) and adaptation (the adjustment of management over time). This framework operationalizes monitoring a necessary component of decision making in the sagebrush biome. Several national and regional monitoring efforts are underway across the sagebrush biome for both vegetation and wildlife. Sustaining these efforts and using the information effectively is an important step towards realizing the full potential of the adaptive management framework in sagebrush ecosystems. Furthermore, coordinating monitoring efforts and information across stakeholders (for example, Federal, State, nongovernmental organizations) will be necessary given the limited resources, diverse ownership/management, and sagebrush biome size.
Spatial aspects of wildlife responses to human-induced habitat change have been examined frequently, yet the temporal dynamics of responses remain less understood. We tested alternative hypotheses for how the abundance of a suite of declining songbirds in relation to energy development changed over time. We conducted point counts at two natural gas fields during two periods spanning a decade (2008–2009 and 2018–2019), and compared the abundance of sagebrush songbirds across a gradient of surface disturbance between study periods (trend-by-time). We also assessed changes in the abundance of birds between study periods relative to additional development that had occurred (trend-over-time). We predicted that abundance responses to surface disturbance would be more negative during the second period, regardless of additional disturbance that had occurred, because of previously observed inverse relationships between surface disturbance and nest survival at our sites. Contrary to our predictions, abundance responses attenuated by the second time period for two of three species, Brewer's sparrow and sage thrasher (the latter at one energy field only). Sagebrush sparrow abundance, however, consistently decreased with surface disturbance within and between periods. Sage thrasher abundance consistently decreased with surface disturbance at one of the gas fields, and the probability of colonization by thrashers between study periods was lower where additional surface disturbance had occurred. Our results highlight the importance of revisiting wildlife responses to anthropogenic habitat changes over time, to clarify the severity and longevity of effects.
USGS sage-grouse and sagebrush ecosystem research is aligned with priority needs outlined in the “Integrated Rangeland Fire Management Strategy Actionable Science Plan” (Integrated Rangeland Fire Management Strategy Actionable Science Plan Team, 2016). The list of 116 research projects is organized into five thematic areas: fire (16 projects); invasive species (7 projects); restoration (23 projects); sagebrush, sage-grouse, and other sagebrush-associated species (60 projects); and weather and climate (10 projects). Individual projects often overlap multiple themes (for example, effects of wildfire and invasive annual grasses on greater sage-grouse habitat); therefore, project descriptions are organized according to the main focal theme.
Anthropogenic activities are changing landscapes and the context in which predator–prey dynamics evolved, thereby altering key ecological processes and community structure. Yet, the specific mechanisms underlying such changes are rarely understood. We tested whether a mesopredator release explained increased rodent density and concomitant predation of songbird nests near natural gas development. From 2015 to 2016, we surveyed apex predators (coyotes, badgers, raptors, and corvids) and measured apparent survival and perceived predation risk of deer mice (Peromyscus maniculatus; a primary nest predator), at 12 plots spanning a gradient of surface disturbance caused by energy development in Wyoming, USA. Additionally, we measured densities of three nest predators: deer mice, least chipmunks (Tamias minimus), and thirteen‐lined ground squirrels (Ictidomys tridecemlineatus). Contrary to the mesopredator release hypothesis, counts of apex predators and perceived predation risk of deer mice increased with surface disturbance from energy development, whereas apparent survival of mice decreased. Densities of mice and ground squirrels, however, increased with surface disturbance, despite increased predation pressure. We therefore rejected the mesopredator release hypothesis as a potential mechanism underlying altered trophic dynamics near energy development. Our results suggest that apex predator control measures would not benefit declining songbirds on natural gas fields. Rather, apex predator abundance may be regulated from the bottom‐up by rodents in this system. Our results corroborate a pattern showing weakened effects of mesopredator release in habitats modified by humans. Understanding how predator–prey dynamics may be altered in novel environments requires an understanding of how predators and prey alike respond to habitat change under different contexts.
Habitat destruction, characterized by patch loss and fragmentation, is a major driving force of species
extinction, and understanding its mechanisms has become a central issue in biodiversity conservation.
Numerous studies have explored the effect of patch loss on food web dynamics, but ignored the critical
role of patch fragmentation. Here we develop an extended patch-dynamic model for a tri-trophic
omnivory system with trophic-dependent dispersal in fragmented landscapes. We found that species
display different vulnerabilities to both patch loss and fragmentation, depending on their dispersal
range and trophic position. The resulting trophic structure varies depending on the degree of habitat
loss and fragmentation, due to a tradeoff between bottom-up control on omnivores (dominated by
patch loss) and dispersal limitation on intermediate consumers (dominated by patch fragmentation).
Overall, we find that omnivory increases system robustness to habitat destruction relative to a simple
food chain.
Modification of habitat structure due to invasive plants can alter the risk landscape for wildlife by, for example, changing the quality or availability of refuge habitat. Whether perceived risk corresponds with actual fitness outcomes, however, remains an important open question. We simultaneously measured how habitat changes due to a common invasive grass (cheatgrass, Bromus tectorum) affected the perceived risk, habitat selection, and apparent survival of a small mammal, enabling us to assess how well perceived risk influenced important behaviors and reflected actual risk. We measured perceived risk by nocturnal rodents using a giving-up density foraging experiment with paired shrub (safe) and open (risky) foraging trays in cheatgrass and native habitats. We also evaluated microhabitat selection across a cheatgrass gradient as an additional assay of perceived risk and behavioral responses for deer mice (Peromyscus maniculatus) at two spatial scales of habitat availability. Finally, we used mark-recapture analysis to quantify deer mouse apparent survival across a cheatgrass gradient while accounting for detection probability and other habitat features. In the foraging experiment, shrubs were more important as protective cover in cheatgrass-dominated habitats, suggesting that cheatgrass increased perceived predation risk. Additionally, deer mice avoided cheatgrass and selected shrubs, and marginally avoided native grass, at two spatial scales. Deer mouse apparent survival varied with a cheatgrass–shrub interaction, corresponding with our foraging experiment results, and providing a rare example of a native plant mediating the effects of an invasive plant on wildlife. By synthesizing the results of three individual lines of evidence (foraging behavior, habitat selection, and apparent survival), we provide a rare example of linkage between behavioral responses of animals indicative of perceived predation risk and actual fitness outcomes. Moreover, our results suggest that exotic grass invasions can influence wildlife populations by altering risk landscapes and survival.
DOWNLOAD this article in Blog Alex Bager (http://bab.empreendedor-academico.com.br/).
Context
Increased edge density is among the main negative effects of habitat loss and fragmentation. Roads are linear infrastructures that may promote barrier effects due to disturbance and mortality effects. We hypothesized that edges of habitat patches bordered by roads are less permeable than roadless edges.
Objectives
We tested whether edge permeability and avoidance are influenced by the presence of paved and dirt roads bordering habitat patches, relatively to roadless edges.
Methods
We translocated 55 montane akodonts (Akodon montensis) from the interior of vegetation remnants to their edges, and tracked fine-scale movements using spool-and-line devices. Edges were bordered by dirt roads (n = 12 mice), paved roads (n = 21) or were not bordered by roads (n = 22). We assessed edge permeability by comparing the number of tracks with crossings, and by comparing the empirical data to simulated correlated random walks. We also assessed edge avoidance by comparing the net direction travelled and net displacement from edge.
Results
No edge crossings were recorded in roaded edges, whereas 36% of tracks in roadless edges crossed the edge at least once. Simulations indicated a significantly lower permeability of roaded edges, while the observed number of crossings in roadless edges was within the expected range. We found no evidence of higher avoidance of roaded edges, as both net direction travelled and displacement were similar across edge types.
Conclusions
Roads decreased edge permeability for the montane akodont. This is likely to increase population isolation among vegetation remnants by reducing the structural connectivity in the already fragmented landscape.
Vole population cycles are a major force driving boreal ecosystem dynamics in northwestern Eurasia. However, our understanding of the impact of winter on these cycles is increasingly uncertain, especially because climate change is affecting snow predictability , quality, and abundance. We examined the role of winter weather and snow conditions, the lack of suitable habitat structure during freeze-thaw periods, and the lack of sufficient food as potential causes for winter population crashes. We live-trapped bank voles Myodes glareolus on 26 plots (0.36 ha each) at two different elevations (representing different winter conditions) in southeast Norway in the winters 2013/2014 and 2014/2015. We carried out two manipulations: supplementing six plots with food to eliminate food limitation and six plots with straw to improve habitat structure and limit the effect of icing in the subnivean space. In the first winter, all bank voles survived well on all plots, whereas in the second winter voles on almost all plots went extinct except for those receiving supplemental food. Survival was highest on the feeding treatment in both winters, whereas improving habitat structure had no effect. We conclude that food limitation was a key factor in causing winter population crashes. K E Y W O R D S climate, feeding experiment, habitat quality, population dynamics, rodents
In North America, it has been shown that cattle in warmer, drier grasslands have lower quality diets than those cattle grazing cooler, wetter grasslands, which suggests warming will increase nutritional stress and reduce weight gain. Yet, little is known about how the plant species that comprise cattle diets change across these gradients and whether these shifts in dietary quality coincide with shifts in dietary composition, i.e. the relative abundance of different plant species consumed by cattle. To quantify geographic patterns in dietary composition, we analyzed the dietary composition and dietary quality of unsupplemented cattle from 289 sites across the central US by sequence-based analyses of plant DNA isolated from cattle fecal samples. Overall, assuming that the percentage of reads for a species in a sample corresponds to the percentage of protein derived from the species, only 45% of the protein intake for cattle was derived from grasses. Within the Great Plains, northern cattle relied more on grasses than southern cattle, which derived a greater proportion of their protein from herbaceous and woody eudicots. Eastern cattle were also more likely to consume a unique assemblage of plant species than western cattle. High dietary protein was not strongly tied to consumption of any specific plant species, which suggests that efforts to promote individual plant species may not easily remedy protein deficiencies. A few plant species were consistently associated with lower quality diets. For example, the diets of cattle with high amounts of Elymus or Hesperostipa were more likely to have lower crude protein concentrations than diets with less of these grasses. Overall, our analyses suggest that climatic warming will increase the reliance of cattle on eudicots as protein concentrations of grasses decline. Monitoring cattle diet with this DNA-based sequencing approach can be an effective tool for quantifying cattle diet to better increase animal performance and guide mitigation strategies to changing climates.
Plant cover is measured by different methods and it is important to be able to estimate mean cover and to compare estimates of plant cover across different sampling methods in a coherent statistical framework. Here, a framework that incorporates (1) pin-point cover data, (2) visually determined cover data, and (3) ordinal cover classification systems (e.g., Braun-Blanquet cover data) is presented and tested on simulated plant cover data. The effect of measurement error when applying a visual determination of plant cover is considered. Generally, the estimation of the mean plant cover was well-behaved and unbiased for all the three methods, whereas the estimate of the intra-plot correlation tended to be upward biased and especially so if the plant cover data was collected using the Braun-Blanquet method. It was surprising that the Braun-Blanquet sampling procedure provided mean plant cover estimates that were comparable to the other sampling schemes. This method shows promise in the attempt to use the large amount of historic Braun-Blanquet plant cover data in the investigation of the underlying causes for observed vegetation changes.
Shrub-dominated arid and semiarid ecosystems are characterized by spatial patterns in vegetation and bare ground (e.g., resource islands). Modern oil and gas well pad construction entails complete removal of vegetation and upper soil layers, followed by replacement of soils and attempts at revegetation; historically, many pads were merely abandoned. Feedbacks between soil and vegetation are required for the recovery of ecosystem functions in these catastrophically disturbed systems. We measured soil organic carbon (SOC), employing a spatially explicit sampling protocol, on two sites in undisturbed big sagebrush communities and a chronosequence of eight recovering well pads. Sites in undisturbed communities exhibited significant spatial autocorrelation of SOC at the plot level that was absent from all of the well pad sites. Incorporating shrub presence as a covariate revealed three additional cases of SOC spatial autocorrelation on well pads. These results, along with SOC patterns between and under plants, suggest resource island development. These findings support the hypothesis that species identity as well as functional group need to be taken into account in restoration. Restoration of ecosystem functions, including those associated with resistance and resilience to disturbance, may be enhanced when characteristic soil heterogeneity and vegetation spatial patterns recover. [Open Access: http://dx.doi.org/10.1890/13-1698.1]
We investigated the influence of vegetation structure and fire history on the foraging behaviour of small rodents (Notomys mitchellii, Pseudomys hermannsburgensis and Mus musculus) by conducting giving-up density (GUD) experiments in recently burnt (9 to 13 years since last fire) and long unburnt shrublands (>40 years), and open and sheltered microhabitats, in a semi-arid region of Western Australia. We predicted that rodents would spend less time foraging in recently burnt shrublands and in open microhabitat and that the influence of microhabitat would be weaker in long unburnt compared to more recently burnt vegetation. Our findings show that fire history and microhabitat structure influence the foraging behaviour of the study species and that the influence of microhabitat varies between fire histories. GUDs were higher in long unburnt vegetation and in open microhabitats. There was a microhabitat effect in recently burnt vegetation, but not in long unburnt. Rodents foraged more in sheltered microhabitats probably because predator encounters are less likely to occur there and it provides them with greater refuge from predation. The presence of a microhabitat effect in recently burnt, but not long unburnt vegetation suggests that understorey vegetation density is more important in mediating predation risk than canopy density. Future studies of small mammal responses to land management actions should include behavioural, as well as population-level responses to differing fire regimes.
Maximum likelihood or restricted maximum likelihood (REML) estimates of the
parameters in linear mixed-effects models can be determined using the lmer
function in the lme4 package for R. As for most model-fitting functions in R,
the model is described in an lmer call by a formula, in this case including
both fixed- and random-effects terms. The formula and data together determine a
numerical representation of the model from which the profiled deviance or the
profiled REML criterion can be evaluated as a function of some of the model
parameters. The appropriate criterion is optimized, using one of the
constrained optimization functions in R, to provide the parameter estimates. We
describe the structure of the model, the steps in evaluating the profiled
deviance or REML criterion, and the structure of classes or types that
represents such a model. Sufficient detail is included to allow specialization
of these structures by users who wish to write functions to fit specialized
linear mixed models, such as models incorporating pedigrees or smoothing
splines, that are not easily expressible in the formula language used by lmer.
A recurrent challenge in the conservation of wide-ranging, imperiled species is understanding which habitats to protect and whether we are capable of restoring degraded landscapes. For Greater Sage-grouse (Centrocercus urophasianus), a species of conservation concern in the western United States, we approached this problem by developing multi-scale empirical models of occupancy in 211 randomly located plots within a 40 million ha portion of the species' range. We then used these models to predict sage-grouse habitat quality at 826 plots associated with 101 post-wildfire seeding projects implemented from 1990 to 2003. We also compared conditions at restoration sites to published habitat guidelines. Sage-grouse occupancy was positively related to plot- and landscape-level dwarf sagebrush (Artemisia arbuscula, A. nova, A. tripartita) and big sagebrush steppe prevalence, and negatively associated with non-native plants and human development. The predicted probability of sage-grouse occupancy at treated plots was low on average (0.09) and not substantially different from burned areas that had not been treated. Restoration sites with quality habitat tended to occur at higher elevation locations with low annual temperatures, high spring precipitation, and high plant diversity. Of 313 plots seeded after fire, none met all sagebrush guidelines for breeding habitats, but approximately 50% met understory guidelines, particularly for perennial grasses. This pattern was similar for summer habitat. Less than 2% of treated plots met winter habitat guidelines. Restoration actions did not increase the probability of burned areas meeting most guideline criteria. The probability of meeting guidelines was influenced by a latitudinal gradient, climate, and topography. Our results suggest that sage-grouse are relatively unlikely to use many burned areas within 20 years of fire, regardless of treatment. Understory habitat conditions are more likely to be adequate than overstory conditions, but in most climates, establishing forbs and reducing cheatgrass dominance is unlikely. Reestablishing sagebrush cover will require more than 20 years using past restoration methods. Given current fire frequencies and restoration capabilities, protection of landscapes containing a mix of dwarf sagebrush and big sagebrush steppe, minimal human development, and low non-native plant cover may provide the best opportunity for conservation of sage-grouse habitats.
Resource managers and scientists need efficient, reliable methods for quantifying vegetation to conduct basic research, evaluate land management actions, and monitor trends in habitat conditions. We examined three methods for quantifying vegetation in 1-ha plots among different plant communities in the northern Great Basin: photography-based grid-point intercept (GPI), line-point intercept (LPI), and point-quarter (PQ). We also evaluated each method for within-plot subsampling adequacy and effort requirements relative to information gain. We found that, for most functional groups, percent cover measurements collected with the use of LPI, GPI, and PQ methods were strongly correlated. These correlations were even stronger when we used data from the upper canopy only (i.e., top ''hit'' of pin flags) in LPI to estimate cover. PQ was best at quantifying cover of sparse plants such as shrubs in early successional habitats. As cover of a given functional group decreased within plots, the variance of the cover estimate increased substantially, which required more subsamples per plot (i.e., transect lines, quadrats) to achieve reliable precision. For GPI, we found that that six–nine quadrats per hectare were sufficient to characterize the vegetation in most of the plant communities sampled. All three methods reasonably characterized the vegetation in our plots, and each has advantages depending on characteristics of the vegetation, such as cover or heterogeneity, study goals, precision of measurements required, and efficiency needed.
Populations of Henslow's Sparrows (Ammodramus henslowii) arc declining, and loss of habitat is a likely factor. Coal mine reclamation has created grassland habitat in Kentucky and elsewhere, and information is needed concerning the use of these areas by Henslow's Sparrows. We compared the behavior and ecology of populations on reclaimed sites and non-mined sites in west-central Kentucky during the 2000 and 2001 breeding seasons. Territories were smaller on the reclaimed sites than unmined sites, perhaps due to differences in habitat quality. Insect sweeps revealed more prey biomass on reclaimed sites than unmined sites. Twenty-eight of 48 nests (58%) fledged at least one young, and nesting success was similar on reclaimed and unmined sites. Mean clutch size was 3.75, with no difference between reclaimed and unmined sites. Similarly, the mean number of fledglings per nest was similar on reclaimed and unmined sites. Multivariate analysis revealed differences in the characteristics of vegetation on reclaimed areas and unmined areas. Reclaimed areas had more grass cover and greater vegetation density, probably due to differences in management history (i.e., mowing or burning) and species composition. Our results indicate that the nesting success of Henslow's Sparrows on reclaimed surface mines in Kentucky is comparable to that on unmined areas. As such, the thousand of hectares of reclaimed surface mines in Kentucky and elsewhere could play an important role in stabilizing populations of Henslow's Sparrows.
Animals make directional movements toward resources to satisfy nutritional, reproductive, and protection needs. We evaluated resource selection by the spiny rat (Thrichomys fosteri) in a heterogeneous habitat, disentangling the relative importance of habitat structure, escape cover, food availability, and intraspecific competition. The last 2 variables were estimated directly by explicitly incorporating their spatiotemporal variation in the model. We radiotracked 15 males and 5 females for a median of 10 days per month for 17 months. Used and available resources were estimated at the home-range scale by intersecting the radiotracking locations (used) and random points (available) with resource maps that were either temporally static (measured only once; palm density and bromeliad cover) or dynamic (with temporal variation; arthropod biomass and conspecific abundance). We performed a resource selection function analysis using conditional logistic regression stratified by each individual location. Within their home ranges, spiny rats selected areas with high bromeliad cover and arthropod biomass. There was a negative interaction between conspecific abundance and arthropod biomass. We showed that resource selection by individuals takes into account multiple resources that vary in space and time. Individuals tended to select areas with high escape cover and high food availability balanced by low intraspecific competition.
Scientific investigation is of value only insofar as relevant results are obtained and communicated, a task that requires organizing, evaluating, analysing and unambiguously communicating the significance of data. In this context, working with ecological data, reflecting the complexities and interactions of the natural world, can be a challenge. Recent innovations for statistical analysis of multifaceted interrelated data make obtaining more accurate and meaningful results possible, but key decisions of the analyses to use, and which components to present in a scientific paper or report, may be overwhelming. We offer a 10-step protocol to streamline analysis of data that will enhance understanding of the data, the statistical models and the results, and optimize communication with the reader with respect to both the procedure and the outcomes. The protocol takes the investigator from study design and organization of data (formulating relevant questions, visualizing data collection, data exploration, identifying dependency), through conducting analysis (presenting, fitting and validating the model) and presenting output (numerically and visually), to extending the model via simulation. Each step includes procedures to clarify aspects of the data that affect statistical analysis, as well as guidelines for written presentation. Steps are illustrated with examples using data from the literature. Following this protocol will reduce the organization, analysis and presentation of what may be an overwhelming information avalanche into sequential and, more to the point, manageable, steps. It provides guidelines for selecting optimal statistical tools to assess data relevance and significance, for choosing aspects of the analysis to include in a published report and for clearly communicating information. © 2016 The Authors. Methods in Ecology and Evolution
Food subsidies have become a widely available and predictable resource in human-modified landscapes for many vertebrate species. Such resources can alter individual foraging behavior of animals, and induce population-wide changes. Yet, little consensus exists about the relative influence of the availabilities of native and human food subsidies to wildlife foraging throughout altered landscapes. We explored this unresolved question by analyzing the effects of landscape factors on American black bear (Ursus americanus) diet across the state of Colorado, USA. We estimated assimilated diet using stable isotope analysis of harvested black bear tissues to determine the contribution of human-derived foods to bear diets throughout Colorado, as well as how increasing reliance on human-derived food subsidies increases the risk of conflict. We found that bears (n = 296) showed strong regional diet variability, but substantial use of human-derived food subsidies in eastern Colorado (> 30% assimilated diet). The age-sex class of the bear and housing density of its harvest location were the most influential predictors of 13C enrichment (a tracer of human food subsidies). Furthermore, foraging on subsidies increased risk of conflict; the odds of being a nuisance bear increased by 60% for each ~ 1‰ increase in δ13C. Our study confirms the efficacy of δ13C as a proxy for human activity, and indicates that while demographic differences play a clear role in the foraging ecology of bears, availability of subsidies coincident with varying levels of human activity appears to be a major driver in predicting black bear diet throughout the western United States.
In 2013, the price of oil averaged $98 per barrel (West Texas Intermediate spot price), up from $94 per barrel in 2012. Prices remain high in early 2014 (near $100 per barrel) and are projected by the Energy Information Administration (EIA) to average in the mid-$90 per barrel range through 2014. A number of proposals designed to increase domestic energy supply, enhance security, and/or amend the requirements of environmental statutes are before the 113th Congress. A key question in this discussion is how much oil and gas is produced in the United States each year and how much of that comes from federal versus nonfederal areas. Oil production has fluctuated on federal lands over the past five fiscal years but has increased dramatically on nonfederal lands. Nonfederal crude oil production has been rapidly increasing in the past few years partly due to favorable geology and the relative ease of leasing from private parties, rising by 2.1 million barrels per day (mbd) between FY2009-FY2013, causing the federal share of total U.S. crude oil production to fall by nearly 11%. Natural gas prices, on the other hand, have remained low for the past several years, allowing gas to become much more competitive with coal for power generation. The shale gas boom has resulted in rising supplies of natural gas. Overall, annual U.S. natural gas production rose by about four trillion cubic feet (tcf) or 19% since FY2009, while production on federal lands (onshore and offshore) fell by about 28%. Natural gas production on non-federal lands grew by 33% over the same time period. The big shale gas plays are primarily on non-federal lands and are attracting a significant portion of investment for natural gas development. The number of producing acres may or may not be a function of how many acres are leased, and the number of acres leased may or may not correlate to the amount of production, but in recent years, some members of Congress have proposed a $4/acre lease fee for non-producing leases. This proposal grew out of the efforts to open more public land and water (offshore) for oil and gas drilling and development when gasoline prices spiked in 2006-2008. Some in Congress noted that there were many leases they believed were not being developed in a timely fashion, while at the same time, others in Congress were pushing for greater access to areas off-limits (such as the Arctic National Wildlife Refuge (ANWR) and areas under leasing moratoria offshore). Higher rents for offshore leases were imposed by the Secretary of the Interior in 2009 to discourage holding unused leases and to move more leases into production, if possible. Another major issue that Congress may seek to address is streamlining the processing of applications for permits to drill (APDs). Some members contend that this would be one way to help boost energy production on federal lands. After a lease has been obtained, either competitively or non-competitively, an APD must be approved for each oil and gas well. Despite the new timeline for review (under the Energy Policy Act of 2005, P.L. 109-58), it took an average of 307 days for all parties to process (approve or deny) an APD in 2011, up from an average of 218 days in 2006. The difference, however, is that in 2006 it took the Bureau of Land Management (BLM) an average of 127 days to process an APD, while in 2011 it took BLM 71 days. In 2006, the industry took an average of 91 days to complete an APD, but in 2011, industry took 236 days. The BLM stated in its FY2012 and FY2013 budget justifications that overall processing times per APD have increased because of the complexity of the process.
Within a species, home-range size can vary due to factors such as sex, mass, age, and breeding condition of individuals as well as habitat type, food availability, population density, and season. The objectives of this study were to estimate home ranges of deer mice (Peromyscus maniculatus) in sage-steppe habitat and to test the hypothesis that several factors (sex, mass, reproductive status, and seasonality) affect home-range size. We also tested the hypothesis that deer mice exhibit home-range fidelity over time. Passive integrated transponder (PIT) technology was used to estimate home ranges in June and September 2006. Home-range estimates varied from 360 m2 to 5868 m2 (65 individuals, 753 observations). Home-range size increased by approximately 60% from June to September. Besides seasonality, none of the other predictors of home range were informative in explaining the variation in home range. Deer mice recaptured in September (3 months after initial capture) had high fidelity in home-range use (42.1% [SE = 8.4%] overlap with 74.1% [SE = 8.7%] area conserved; n = 9). All animals for which home range was estimated in both seasons retained some fraction of their June home range in September. Results support the use of combined location data collected over long periods, such as weeks or months, to estimate home range for deer mice. The results have implications for deer mouse—pathogen ecology, particularly with respect to modeling transmission of Sin Nombre virus—a pathogen that is directly transmitted by deer mice.
1.Demographic consequences of human-induced rapid environmental change (HIREC) have been widely documented for many populations. The mechanisms underlying such patterns, however, are rarely investigated and yet are critical to understand for effective conservation and management.2.We investigated the mechanisms underlying reduced avian nest survival with intensification of natural gas development, an increasing source of HIREC globally. We tested the hypothesis that energy development increased the local activity of important nest predator species thereby elevating nest predation rates. During 2011–2012, we surveyed predators and monitored 668 nests of Brewer's sparrows Spizella breweri, sagebrush sparrows Artemisiospiza nevadensis and sage thrashers Oreoscoptes montanus breeding at twelve sites spanning a gradient of habitat loss from energy development in western Wyoming, USA.3.Nine species, representing four mammalian and three avian families, were video-recorded depredating eggs and nestlings. Important nest predator species differed across songbird species, despite similar nesting habitats. Approximately 75% of depredation events were by rodents.4.Consistent with our predictions, detections of most rodent nest predators increased with surrounding habitat loss due to natural gas development, which was associated with increased probability of nest predation for our three focal bird species.5.An altered nest predator assemblage was therefore at least partly responsible for elevated avian nest predation risk in areas with more surrounding energy development.6.Synthesis and applications. We demonstrate one mechanism, i.e. the local augmentation of predators, by which human-induced rapid environmental change (HIREC) can influence the demography of local populations. Given the accelerating trajectory of global energy demands, an important next step will be to understand why the activity and/or abundance of rodent predators increased with surrounding habitat loss from energy development activities.This article is protected by copyright. All rights reserved.
Natural gas extraction and field development are pervasive throughout the sagebrush steppe of Wyoming. We conducted this study to determine how roads associated with natural gas extraction affect the distribution of breeding songbirds in sagebrush steppe habitat. The study encompassed dirt and paved roads in the Jonah Field II and Pinedale Anticline Project Area in Sublette County, Wyoming. Sites are dominated by Wyoming big sagebrush (Artemisia tridentata), and common passerines include sagebrush obligates: Brewer's Sparrows (Spizella breweri), Sage Sparrows (Amphispiza belli), and Sage Thrashers (Oreoscoptes montanus); and non-obligates: Horned Larks (Eremophila alpestris) and Vesper Sparrows (Pooecetes gramineus). Species relative density was measured using 50-m-radius point counts during spring 1999 and 2000. Four roads with low traffic volumes (700-10 vehicles per day) were surveyed and point counts were centered at variable distances from the road surface such that relative densities were measured 0-600 m from the road's edge. Density of sagebrush obligates, particularly Brewer's and Sage Sparrow, was reduced by 39%-60% within a 100-m buffer around dirt roads with low traffic volumes (700-10 vehicles per day). While a 39%-60% reduction in sagebrush obligates within 100 m of a single road may not be biologically significant, the density of roads created during natural gas development and extraction compounds the effect, and the area of impact can be substantial. Traffic volume alone may not sufficiently explain observed declines adjacent to roads, and sagebrush obligates may also be responding to edge effects, habitat fragmentation, and increases in other passerine species along road corridors. Therefore, declines may persist after traffic associated with extraction subsides and perhaps until roads are fully reclaimed.
Global energy demands continue to result in new and emerging sources of anthropogenic disturbance to populations and systems. Here, we assessed the influence of natural gas development on a critical component of fitness (nest survival) for Brewer’s sparrow (Spizella breweri), sagebrush sparrow (Artemisiospiza nevadensis), and sage thrasher (Oreoscoptes montanus), three species of sagebrush-obligate songbirds that are of conservation concern, and assessed the efficacy of a commonly used index of oil and gas development intensity (well density) for estimating habitat transformation and predicting species’ responses. During 2008–2009 and 2011–2012 we monitored 926 nests within two natural gas fields in western Wyoming, USA. We calculated landscape metrics (habitat loss, amount of edge, patch shape complexity, and mean patch size) to identify the aspect of landscape transformation most captured by well density. Well density was most positively associated with the amount of sagebrush habitat loss within 1 square kilometer. Nest survival was relatively invariant with respect to well density for all three species. In contrast, nest survival rates of all three species generally decreased with surrounding habitat loss due to energy development. Thus, although well density and habitat loss were strongly correlated, well density resulted in overly conservative estimates of nest survival probability. Our results emphasize the importance of careful evaluation of the appropriateness of particular indices for quantifying the effects of human-induced habitat change. For managers concerned about the effects of natural gas development or similar forms of human land use to co-occurring breeding birds, we recommend minimizing the amount of associated habitat conversion.
Patterns of habitat selection by small mammals reflect variation in availability of resources at a range of spatial and temporal scales. I investigated use of habitat by northern grasshopper mice (Onychomys leucogaster) in shortgrass prairie and related the patterns to distribution of vegetation and substrate and availability of arthropod prey. I used powder tracking to document use of microhabitats and live-trapping to estimate abundance on sites with different soil types and amounts of shrub cover (macrohabitats). At all spatial scales examined, mice used disturbances of soil (primarily pocket gopher mounds) and burrows more than expected based on abundance of these microhabitats, but showed no affinity for large shrubs. Furthermore, movement patterns suggested that mice concentrated activities in areas with high densities of mounds and burrows. Insect prey were more numerous on mounds than in other microhabitats and were generally more abundant in trapping areas where grasshopper mice were captured, especially in spring and early summer. Mounds and burrows provide arthropods with access to subterranean refuges, and the concentration and accessibility of prey, thus, may explain the intensive use of these microhabitats by mice. Microhabitat variables associated with mounds and burrows were better predictors of population density than was macrohabitat, which may reflect the spatial distribution and temporal predictability of insect prey. Although local abundance of grasshopper mice was best explained by availability of suitable foraging microhabitat, the relationship between these microhabitats and edaphic characteristics suggests that it may be difficult to separate the roles of microhabitat and macrohabitat for this wide-ranging species.
(1) Deermice were supplied with extra food between December 1973 and June 1975. (2) Late-winter addition of food to two areas resulted in more male and female deermice. (3) Immigration to areas with extra food was nearly triple that to controls. (4) The size of home ranges of residents became significantly smaller in populations with extra food. (5) Breeding on control areas was delayed in spring 1974, when weather was poor. However, mice on grids with extra food bred early and began to breed in winter. (6) Mice with extra food produced more young and reached sexual maturity at a lower weight. (7) Extra food reversed the normal winter weight loss so that mice maintained high weights and reproduced in spite of temperate winter weather. (8) The annual fluctuations in numbers of deermice may be a consequence of seasonal reproductive behaviour which is proximately limited by food availability.
Seven of nine common shredder species attained significantly higher adult mass, higher densities, or both when food was supplemented. Larval densities of Malenka spp. and Brilla retifinis were significantly higher when additional food was added. Brillia retifinis densities were >10× greater in high food additions. B. retifinis apparently fills a role as a fugitive in this system and is better able to track shifts in resource abundance by virtue of its short generation time. Zapada cinctipes and Z. haysi were more dense in high and intermediate food input treatments during the last half of the summer. Other taxa had nonsignificant trends to higher densities when extra food was provided. Most of the change in benthic densities can be attributed to decreased rates of emigration with increasing food supply. Six of eight taxa for which adult mass at emergence was measured were significantly more massive (4-46%) when food was added. Females gained proportionately more in most species. The biomass of most taxa increased in proportion to the overall increase in biomass of the common coarse-detritus consumers. The main exceptions were a disproportionate increase in the percentage of the biomass represented by B. retifinis and a decrease in the representation of Z. cinctipes. -from Author
(1) Population density and reproduction in the song sparrow (Melospiza melodia, Wilson) on Mandarte Island, B.C. varied widely from 1975 to 1986. Several measures of reproductive success declined as population density increased by six times. At peak density, females produced only one-quarter the number of young produced at low densities. (2) We provided supplemental food to sixteen of seventy-two pairs before and during the breeding period in 1985, a year of peak density, to test the hypothesis that the amount of food available per pair declines as density increases and thus regulates reproduction. (3) Supplemental food (i) advanced laying date; (ii) increased clutch size, the number of breeding attempts, nestling weight and the number of independent young produced; and (iii) reduced brood parasitism and the interval between successful nesting attempts. (4) There was no difference in the subsequent survival or reproduction of fed and control young. (5) Supplemental food was associated with reduced adult survival to the next breeding season, perhaps because of increased competition for territories with feeders after the feeding experiment. (6) We conclude that food supply is important in regulating reproduction, and that food availability in the breeding period could limit population size.
We obtained a complete census of vegetation in a 30- x 1,900-m plot in the Sonoran Desert (Tumamoc Hill, Pima County, Ariz.). We then evaluated the accuracy of 5 sampling techniques commonly used to sample vegetation in deserts: step-point, point-quarter, and 3 line-intercept methods. We compared presence and percent occurrence for each method with the census. The line-intercept (method 3) most closely estimated the census: it was closer for all species occurring on >1% of the site, revealed the least variability relative to sample size for dominant species, and accounted for more (20 of 23) plant species on the study site than the other methods.
The decline of greater sage grouse (Centrocercus urophasianus) over the last 50 years has raised concern over how natural gas development might affect sage grouse populations. We examined the effects of vehicular activity due to gas-well development near Pinedale, Wyoming, on productivity and movements of sage grouse. In 1998-1999, we captured and radiomarked 48 female sage grouse on 6 leks classified as disturbed or undisturbed, based on the presence or absence of natural gas development within 3 km. The mean distance from disturbed leks to selected nest sites was greater (P=0.019 with outliers removed, P=0.004 with outliers included) than distance moved from undisturbed leks. Nest-initiation rate for hens from disturbed leks was 65%, while hens from undisturbed leks initiated nests 89% (P=0.07) of the time. Nest success at both disturbed and undisturbed leks was 50%. Our results suggest that light traffic disturbance (1-12 vehicles/day) during the breeding season might reduce nest-initiation rates and increase distances moved from leks during nest-site selection. We recommend further investigation concentrating on hen behavior (i.e., distance moved from lek to nest site, breeding behavior, lek attendance), reproductive effort, and nest success in relation to natural gas development as development intensifies.
A key issue in animal behaviour is the need to understand variation in behavioural responses to human-induced rapid environmental change (HIREC) such as habitat loss, exotic species, pollution, human harvesting and climate change. Why do some individuals show maladaptive behaviours, while others show adaptive responses to evolutionarily novel situations? At present, we lack a unified conceptual framework for generating predictions and guiding empirical and theoretical work on this critical question. Drawing from the concept of ecological traps, I suggest that a conceptual framework for explaining this variation should include four main points: (1) behavioural responses (adaptive or not) are the result of cueeresponse systems, or behavioural 'rules of thumb'; (2) limited or imprecise, unreliable information often underlies suboptimal behaviour; (3) the organism's behavioural flexibility affects its response to novel situations; and (4) evolution (and development) in past environments has shaped cueeresponse systems, responses to imperfect information and degree of behavioural flexibility to be adaptive in past environments, but not necessarily in novel environments. The degree of match/mismatch between past environments and novel environments altered by HIREC is thus a key to explaining adaptive versus maladaptive behaviours. I suggest several existing frameworks that address these four points, and are thus potentially useful for explaining behavioural responses to HIREC: signal detection theory, adaptive plasticity theory, extended reaction norms and cost-benefit theory on variation in learning. I further discuss more complex aspects of reality that would be useful to add to these existing frameworks. (c) 2013 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
This paper analyzes the impact of small-mammal activity on the standing crop of vegetation on areas reclaimed after coal strip- mining in northeastern Wyoming. The small-mammal community included 2 carnivorous, 2 herbivorous, and 4 omnivorous species. Deer mine (Peromysucs maniculatus ) dominated the population on all areas, constituting 85.4% of small mammals live-trapped. Plant species preferred as food by deer mice included sainfoin (Onobrychis viciaefolia), fireweed summercypress, (Kochia scopa- ria), and fourwing saltbush (Atriplex canescens). Grasses had lower preference rankings than forbs. The deer mouse population consumed 20 g/ha/day of plant matter. They consumed 0.11% of the aboveground peak standing crop (PSC) during the growing season, and the consumption of the total small-mammal commun- ity was less than 1% of PSC. However, the PSC of sainfoin was significantly affected by grazing of small-mammal populations. Large tracts of land in the shortgrass prairie of the Northern Great Plains have been strip-mined for coal and require reclama- tion to levels of productivity that existed before the disturbance. Understanding the role of plant-animal interactions in the reestab- lishment of vegetation after reclamation is essential to designing successful reclamation procedures for strip-mined land. Small Mammals can limit the effectiveness of seedings on rangeland (Nelson et al. 1970), burned brushlands (Howard 1950), and dis- rupted forest habitat (Radvanyi 1980. Grazing by small mammals specifically has been found to decrease primary production in arctic tundra (Batzli 1975) and desert scrub (Soholt 1973) and the
Anti-predator behavior can affect prey growth, reproduction, survival, and generate emergent effects in food webs. Small mammals often lower the cost of predation by altering their behavior in response to shrubs,but the importance of other microhabitat features, such as downed woody debris, for anti-predator behavior is unknown. We used givingup densities to quantify the degree to which downed woody debris alters perceived predation risk by small mammals in southeastern pineforests. We placed 14 foraging trays next to large downed woody debris,shrubs, and in open areas for 12 consecutive nights. Moon illumination, a common indicator of predation risk, led to a similar reduction in small mammal foraging in all three microhabitats (open, downed woody debris,and shrub). Small mammals perceived open microhabitats as riskier than shrub microhabitats, with downed woody debris habitats perceived as being of intermediate risk between shrub and open microhabitats. Despite the presumed benefits of the protective cover of downed woody debris, small mammals may perceive downed woody debris as a relatively risky foraging site in southeastern pine forests where the high diversity and abundance of rodent-eating snakes may provide a primary predatory threat.
Human-induced rapid environmental change (HIREC; e.g., climate change or exotic species) has caused global species declines. Although behavioral plasticity has buffered some species against HIREC, maladaptive behavioral scenarios called 'evolutionary traps' are increasingly common, threatening the persistence of affected species. Here, we review examples of evolutionary traps to identify their anthropogenic causes, behavioral mechanisms, and evolutionary bases, and to better forecast forms of HIREC liable to trigger traps. We summarize a conceptual framework for explaining the susceptibility of animals to traps that integrates the cost-benefit approach of standard behavioral ecology with an evolutionary approach (reaction norms) to understanding cue-response systems (signal detection). Finally, we suggest that a significant revision of conceptual thinking in wildlife conservation and management is needed to effectively eliminate and mitigate evolutionary traps.
Try out several plant-herbivore models and find one that seems to fit the oscillations shown by Alaskan lemmings
Control of mid-sized mammalian predators (hereafter, mesopredators) is sometimes advocated in an attempt to reduce their impact on wildlife populations, particularly economically important (i.e., game) or endangered species. However, mesopredators may play a role in regulating small mammal populations; thus, lethal control of mesopredators may have unintended consequences. The hispid cotton rat (Sigmodon hispidus; hereafter, cotton rat) is one of the most common small mammals in the southeastern United States and is an important prey species for several of the region's predators. Within fire-maintained communities, such as the longleaf pine (Pinus palustris) forests of the Coastal Plain, cotton rat populations dramatically, yet temporarily, decline following prescribed fire. To evaluate the effects of mesopredator removal on cotton rat survival and cause-specific mortality, we conducted a large-scale mesopredator exclusion experiment that incorporated a prescribed fire during the winter of study. Between 18 May 2006 and 20 June 2007, we used radio-telemetry to monitor 252 cotton rats (131 in exclosures and 121 in controls) and documented 184 mortalities. During the 37-week period of monitoring prior to the prescribed fire event, weekly survival of cotton rats was greater in mesopredator exclusion plots. During the 19 weeks following the prescribed fire, there were no differences in weekly survival relative to mesopredator treatment, but fire caused a short-term reduction in weekly survival within both exclosures and controls. Of 36 cotton rats monitored on the date of prescribed fire, 18 were depredated within 1 month, 4 emigrated, and 5 were killed by the fire event. Overall, raptors preyed on cotton rats more in exclosures than in controls, but evidence for compensatory predation (raptor-caused morality greater in exclosures than in controls although survival rates were similar between treatments) only occurred following the prescribed fire event. Our results suggest that managing mesopredators may result in a temporary increase in cotton rat survival, but dormant season prescribed fire removes this effect until well into the following growing season. © 2011 The Wildlife Society.
Oil and natural gas development in the Intermountain West region of North America has expanded over the last 2 decades, primarily within sagebrush dominated landscapes. Although the effects of energy development on high-profile game species such as the greater sage-grouse (Centrocercus urophasianus) have been documented, studies examining responses of non-game birds are lacking. Simultaneously, many songbirds that breed within sagebrush steppe habitats have shown range-wide population declines that are likely due to widespread habitat loss and alteration. We evaluated songbird abundance and species richness across gradients of oil and natural gas development intensity, as indexed by well density, at 3 energy fields (2 natural gas and 1 oil) in the Upper Green River Basin, Wyoming, USA during 2008–2009. While simultaneously accounting for important habitat attributes, increased well density was associated with significant decreases in Brewer's sparrow (Spizella breweri) and sage sparrow (Amphispiza belli) abundance, particularly in the Jonah natural gas field. Vesper sparrows (Pooecetes gramineus) were also negatively influenced by increased well density. Horned larks (Eremophila alpestris) increased with well density in the Pinedale Anticline natural gas field, and sage thrashers (Oreoscoptes montanus) showed no response to energy development. Species richness was not significantly affected by well density. Results suggest that regional declines of some songbird species, especially sagebrush-obligates, may be exacerbated by increased energy development. Understanding the specific mechanisms underlying responses to energy development is an important next step and will aid land managers in the development of effective mitigation and management strategies for the maintenance of stable bird communities in sagebrush habitat. © 2011 The Wildlife Society.
Millions of ducks, geese, and sandhill cranes (Grus canadensis; hereafter cranes) stop in the Central Platte River Valley (CPRV) of Nebraska to store nutrients for migration and reproduction by consuming corn remaining in fields after harvest. We examined factors that influence use of cornfields by cranes and geese (all mid-continent species combined; e.g., Anser, Chen, and Branta spp.) because it is a key step to efficient conservation planning aimed at ensuring that adequate food resources are available to migratory birds stopping in the CPRV. Distance to night-time roost site, segment of the CPRV (west to east), and agricultural practices (post-harvest treatment of cornfields: idle, grazed, mulched, mulched and grazed, and tilled) were the most important and influential variables in our models for geese and cranes. Probability of cornfield use by geese and cranes decreased with increasing distance from the closest potential roosting site. The use of cornfields by geese increased with the density of corn present there during the early migration period, but field use by cranes appeared not to be influenced by early migration corn density. However, probability of cornfield use by cranes did increase with the amount of wet grassland habitat within 4.8 km of the field. Geese were most likely to use fields that were tilled and least likely to use fields that were mulched and grazed. Cranes were most likely to use fields that were mulched and least likely to use fields that were tilled, but grazing appeared not to influence the likelihood of field use by cranes. Geese were more likely to use cornfields in western segments of the CPRV, but cranes were more likely to use cornfields in eastern segments. Our data suggest that managers could favor crane use of fields and reduce direct competition with geese by reducing fall and spring tilling and increasing mulching. Moreover, crane conservation efforts would be most beneficial if they were focused in the eastern portions of the CPRV and in fields as close as possible to both known roosting and large amounts of wet grassland habitats. © 2011 The Wildlife Society.