Predation Risk, Elk, and Aspen: Comment

With the exception of humans, gray wolves (Canis lupus) are perhaps the most significant predator of cervids in the northern hemisphere, mainly due to the group-hunting, year-round activity, and widespread geographic distribution (Peterson et al. 2003). Thus, interactions between wolves and large herbivore prey, such as elk (Cervus elaphus) and moose (Alces alces), have long been of interest to biologists (Peterson 1995, Jęodrzejewska et al. 2000, Mech and Boitani 2003). The potential ecological role this apex predator may have, via trophic cascades, has also received attention in recent years by researchers (e.g., Callan et al. 2013, Kuijper et al. 2013, 2014), wildlife management agencies (e.g., state wolf management plans), as well as the general public. Perhaps nowhere in the western United States has a heightened examination of this large predator been more focused than in Yellowstone National Park (YNP; Laundré et al. 2001, Smith et al. 2003, 2013, Fortin et al. 2005). Here, wolves were reintroduced in the mid-1990s, again completing the park\u27s large predator guild after approximately seven decades of absence, thus providing a long-term, landscape-scale, natural experiment (Diamond 1983). The Gallatin winter range is one of two that occur along the northern portion of YNP, the other is the northern ungulate winter range, or “northern range,” located some 25 km or more to the east. Of these, the Gallatin has been less studied. Nevertheless, the Gallatin winter range, like the northern range, experienced high levels of elk herbivory following the extirpation of wolves in the early 1900s. Over a period of approximately seven decades, intensive herbivory by elk led to the long-term decline in aspen (Populus tremuloides) and willow (Salix spp.) recruitment (i.e., growth of young plants above the browse level of elk) in the Gallatin winter range, leaving these plant communities in an impoverished condition (Lovaas 1967, Patten 1968, Kay 2001, Ripple and Beschta 2004, Halofsky and Ripple 2008). Accelerated soil and channel erosion also occurred (Lovaas 1967, Beschta and Ripple 2006). Thus, when wolves were reintroduced into Yellowstone in the mid-1990s, aspen recruitment within the Gallatin elk winter range, had been largely absent for several decades (Kay 2001, Halofsky and Ripple 2008). In 2010, Winnie (2012) sampled 65 aspen stands in the northwestern corner of YNP, within the Gallatin elk winter range, to determine if a behaviorally mediated trophic cascade (BMTC) was occurring. As background information Winnie (2012:2600) included only a single sentence about wolves in the Greater Yellowstone Ecosystem and the remainder of the paragraph briefly discussed elk numbers, with most of the emphasis on elk in YNP\u27s northern range where there has been a pronounced redistribution of elk since the reintroduction of wolves (White et al. 2012). A more complete summary regarding the status and dynamics of wolves and elk over the last 15 years (i.e., 1995–2010) in the Gallatin elk winter range, as well as in the Daly Creek sub-drainage where Winnie\u27s study occurred, would have helped readers better understand the context of his study. Furthermore, information regarding human harvest of elk in the Gallatin winter range since the return of wolves, or whether such hunting has been affecting elk numbers or distribution in recent years was not provided. As part of his 2010 field study, Winnie (2012) characterized the presence or absence of several hypothesized risk factors (independent variables) for each aspen stand, including escape impediments, visual impediments, distance to conifer forest edge, and presence of deadfall trees. For dependent variables, Winnie (2012) recorded the presence or absence of browsing on aspen suckers (ramets \u3c2 m in height) and the number of aspen juveniles (plants \u3e2 m in height but \u3c6 cm in diameter at breast height). A height of 2 m generally represents the upper browse level of elk, and young aspen exceeding this height are considered to have successfully recruited. Such recruitment would represent a major departure from the browsing suppression that occurred in his study area over recent decades (Kay 2001, Halofsky and Ripple 2008) and an indication that a tri-trophic cascade involving wolves, elk, and aspen may be underway. From the results of his analyses, Winnie (2012:2600) concluded that “aspen were not responding to hypothesized fine-scale risk factors in ways consistent with the current BMTC hypothesis.” We respectfully submit that the design and analysis used to support such a conclusion may be deficient for two reasons, the first based on conceptual concerns and the second on statistical concerns. (1) Unfortunately, some aspen stands Winnie (2012) sampled contained juveniles associated with “physical barriers,” barriers that could prevent elk from browsing young aspen. To be scientifically valid, a risk assessment using young aspen as the dependent variable must inherently assure that all evaluated plants were accessible to elk browsing. (2) The inclusion of 10 aspen stands containing some physically protected aspen likely confounded results from his predation risk analyses (i.e., Figs. 5, 6, and 7 in Winnie 2012). While the inclusion of stands with protected aspen may increase the variance associated with his dependent variables (i.e., browsing rate, number of juveniles), the fallacy of doing so is revealed by inspecting these variables for the 85% of his stands (n = 55 stands) that did not have physically protected aspen. Here, a browsing rate of ∼99% and an average of \u3c1 juvenile per stand occurred (back-transformed means from Fig. 8b and a, respectively [Winnie 2012:2609]), indicating a general lack of variance in the dependent variables associated with these stands and little likelihood of a statistically significant outcome. Thus, we suspect that the “statistically significant” results Winnie (2012) found in Figs. 5, 6, and 7, whether contrary to or in support of a BMTC hypothesis, are primarily influenced by the occurrence of risk factors associated with those stands where some of the young aspen were physically protected. A reanalysis by Winnie of browsing rate and number of juveniles vs. his risk factors, using just the 55 stands accessible to elk, could clarify this issue. Because of the above concerns, we would offer that results of Winnie\u27s (2012) analyses of “proportion of sprouts browsed” or “number of juveniles per stand” relative to his hypothesized risk factors may well be spurious. If so, any discussions and conclusions based on those results are in question. A 2004 field study of aspen stands in the Gallatin winter range found aspen recruitment had declined precipitously following the extirpation of wolves in the 1920s and remained essentially absent through the late 1990s (Halofsky and Ripple 2008). Thus, when Winnie (2012) undertook his field study in 2010, a wolf–elk–aspen trophic cascade had not yet been confirmed. While the occurrence of juvenile aspen would be important to the long-term survival of aspen stands, the data for elk-accessible stands continue to show exceptionally high browse rates and little or no recruitment (Winnie 2012). This situation contrasts with YNP\u27s northern range where decreased browsing and increased heights of young aspen in portions of that range have been observed some 6–10 years after the occurrence of increased willow growth, although this recruitment has been spatially patchy (e.g., Ripple and Beschta 2012, Painter 2013; also see northern range photos of aspen recruitment available online).5 It should be noted that decreased browsing and increased heights of willows in the Gallatin winter range (at the base of the Daly Creek watershed) following the return of wolves, and consistent with the occurrence of a trophic cascade, were documented as early as 1999–2000 (Ripple and Beschta 2004), with heights continuing to increase in more recent years (Beschta and Ripple 2010). Also consistent with a trophic cascade, various northern range studies have found increased willow growth/canopy cover, sometimes interacting with climatic fluctuations, following wolf reintroduction (e.g., Groshong 2004, Beschta and Ripple 2007, Beyer et al. 2007, Baril 2009, Tercek et al. 2010, Marshall 2012). The occurrence of 192 juvenile aspen within Winnie\u27s (2012) study area would seem to indicate the beginnings of a tri-trophic cascade, particularly when compared to the lack of juvenile production in the decades immediately before wolf reintroduction (Halofsky and Ripple 2008). However, most of the 192 juveniles were associated with aspen stands characterized as having some degree of physical protection from elk (Fig. 8a in Winnie 2012), making it difficult to confirm if they represent a wolf–elk–aspen trophic cascade involving density and/or behavioral mediation. A trophic cascade involving aspen can be complex and context dependent (e.g., linked to bottom-up factors such as fire [Eisenberg et al. 2013]). Furthermore, undertaking risk assessments associated with large mammalian predators and ungulates in mountainous terrain, where human hunting is also occurring across part of the landscape, can be especially challenging. While we commend Winnie (2012) for attempting such an assessment, without a reanalysis of only those young aspen accessible to elk it would appear that his evaluation may not have been sufficiently rigorous to evaluate the presence or absence of a potential BMTC in the Gallatin winter range

Foraging Decisions in Risk-Uniform Landscapes

Behaviour is shaped by evolution as to maximise fitness by balancing gains and risks. Models on decision making in biology, psychology or economy have investigated choices among options which differ in gain and/or risk. Meanwhile, there are decision contexts with uniform risk distributions where options are not differing in risk while the overall risk level may be high. Adequate predictions for the emerging investment patterns in risk uniformity are missing. Here we use foraging behaviour as a model for decision making. While foraging, animals often titrate food and safety from predation and prefer safer foraging options over riskier ones. Risk uniformity can occur when habitat structures are uniform, when predators are omnipresent or when predators are ideal-free distributed in relation to prey availability. However, models and empirical investigations on optimal foraging have mainly investigated choices among options with different predation risks. Based on the existing models on local decision making in risk-heterogeneity we test predictions extrapolated to a landscape level with uniform risk distribution. We compare among landscapes with different risk levels. If the uniform risk is low, local decisions on the marginal value of an option should lead to an equal distribution of foraging effort. If the uniform risk is high, foraging should be concentrated on few options, due to a landscape-wide reduction of the value of missed opportunity costs of activities other than foraging. We provide experimental support for these predictions using foraging small mammals in artificial, risk uniform landscapes. In high risk uniform landscapes animals invested their foraging time in fewer options and accepted lower total returns, compared to their behaviour in low risk-uniform landscapes. The observed trade off between gain and risk, demonstrated here for food reduction and safety increase, may possibly apply also to other contexts of economic decision making

Multi‐dimensional biodiversity hotspots and the future of taxonomic, ecological and phylogenetic diversity: A case study of North American rodents

AimWe investigate geographic patterns across taxonomic, ecological and phylogenetic diversity to test for spatial (in)congruency and identify aggregate diversity hotspots in relationship to present land use and future climate. Simulating extinctions of imperilled species, we demonstrate where losses across diversity dimensions and geography are predicted.LocationNorth America.Time periodPresent day, future.Major taxa studiedRodentia.MethodsUsing geographic range maps for rodent species, we quantified spatial patterns for 11 dimensions of diversity: taxonomic (species, range weighted), ecological (body size, diet and habitat), phylogenetic (mean, variance, and nearest‐neighbour patristic distances, phylogenetic distance and genus‐to‐species ratio) and phyloendemism. We tested for correlations across dimensions and used spatial residual analyses to illustrate regions of pronounced diversity. We aggregated diversity hotspots in relationship to predictions of land‐use and climate change and recalculated metrics following extinctions of IUCN‐listed imperilled species.ResultsTopographically complex western North America hosts high diversity across multiple dimensions: phyloendemism and ecological diversity exceed predictions based on taxonomic richness, and phylogenetic variance patterns indicate steep gradients in phylogenetic turnover. An aggregate diversity hotspot emerges in the west, whereas spatial incongruence exists across diversity dimensions at the continental scale. Notably, phylogenetic metrics are uncorrelated with ecological diversity. Diversity hotspots overlap with land‐use and climate change, and extinctions predicted by IUCN status are unevenly distributed across space, phylogeny or ecological groups.Main conclusionsComparison of taxonomic, ecological and phylogenetic diversity patterns for North American rodents clearly shows the multifaceted nature of biodiversity. Testing for geographic patterns and (in)congruency across dimensions of diversity facilitates investigation into underlying ecological and evolutionary processes. The geographic scope of this analysis suggests that several explicit regional challenges face North American rodent fauna in the future. Simultaneous consideration of multi‐dimensional biodiversity allows us to assess what critical functions or evolutionary history we might lose with future extinctions and maximize the potential of our conservation efforts.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154236/1/geb13050.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154236/2/geb13050_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154236/3/geb13050-sup-0001-Supinfo1.pd

A comparison of the seasonal movements of tiger sharks and green turtles provides insight into their predator-prey relationship

During the reproductive season, sea turtles use a restricted area in the vicinity of their nesting beaches, making them vulnerable to predation. At Raine Island (Australia), the highest density green turtle Chelonia mydas rookery in the world, tiger sharks Galeocerdo cuvier have been observed to feed on green turtles, and it has been suggested that they may specialise on such air-breathing prey. However there is little information with which to examine this hypothesis. We compared the spatial and temporal components of movement behaviour of these two potentially interacting species in order to provide insight into the predator-prey relationship. Specifically, we tested the hypothesis that tiger shark movements are more concentrated at Raine Island during the green turtle nesting season than outside the turtle nesting season when turtles are not concentrated at Raine Island. Turtles showed area-restricted search behaviour around Raine Island for ~3–4 months during the nesting period (November–February). This was followed by direct movement (transit) to putative foraging grounds mostly in the Torres Straight where they switched to area-restricted search mode again, and remained resident for the remainder of the deployment (53–304 days). In contrast, tiger sharks displayed high spatial and temporal variation in movement behaviour which was not closely linked to the movement behaviour of green turtles or recognised turtle foraging grounds. On average, tiger sharks were concentrated around Raine Island throughout the year. While information on diet is required to determine whether tiger sharks are turtle specialists our results support the hypothesis that they target this predictable and plentiful prey during turtle nesting season, but they might not focus on this less predictable food source outside the nesting season

Shallow soils are warmer under trees and tall shrubs across Arctic and Boreal ecosystems

Soils are warming as air temperatures rise across the Arctic and Boreal region concurrent with the expansion of tall-statured shrubs and trees in the tundra. Changes in vegetation structure and function are expected to alter soil thermal regimes, thereby modifying climate feedbacks related to permafrost thaw and carbon cycling. However, current understanding of vegetation impacts on soil temperature is limited to local or regional scales and lacks the generality necessary to predict soil warming and permafrost stability on a pan-Arctic scale. Here we synthesize shallow soil and air temperature observations with broad spatial and temporal coverage collected across 106 sites representing nine different vegetation types in the permafrost region. We showed ecosystems with tall-statured shrubs and trees (>40 cm) have warmer shallow soils than those with short-statured tundra vegetation when normalized to a constant air temperature. In tree and tall shrub vegetation types, cooler temperatures in the warm season do not lead to cooler mean annual soil temperature indicating that ground thermal regimes in the cold-season rather than the warm-season are most critical for predicting soil warming in ecosystems underlain by permafrost. Our results suggest that the expansion of tall shrubs and trees into tundra regions can amplify shallow soil warming, and could increase the potential for increased seasonal thaw depth and increase soil carbon cycling rates and lead to increased carbon dioxide loss and further permafrost thaw

Inter-individual variability of stone marten behavioral responses to a highway

Efforts to reduce the negative impacts of roads on wildlife may be hindered if individuals within the population vary widely in their responses to roads and mitigation strategies ignore this variability. This knowledge is particularly important for medium-sized carnivores as they are vulnerable to road mortality, while also known to use available road passages (e.g., drainage culverts) for safely crossing highways. Our goal in this study was to assess whether this apparently contradictory pattern of high road-kill numbers associated with a regular use of road passages is attributable to the variation in behavioral responses toward the highway between individuals. We investigated the responses of seven radio-tracked stone martens (Martes foina) to a highway by measuring their utilization distribution, response turning angles and highway crossing patterns. We compared the observed responses to simulated movement parameterized by the observed space use and movement characteristics of each individual, but naı¨ve to the presence of the highway. Our results suggested that martens demonstrate a diversity of responses to the highway, including attraction, indifference, or avoidance. Martens also varied in their highway crossing patterns, with some crossing repeatedly at the same location (often coincident with highway passages). We suspect that the response variability derives from the individual’s familiarity of the landscape, including their awareness of highway passage locations. Because of these variable yet potentially attributable responses, we support the use of exclusionary fencing to guide transient (e.g., dispersers) individuals to existing passages to reduce the road-kill risk

Effect of ground squirrel burrows on plant productivity in a cool desert environment

Previous work demonstrated that burrows of Townsend's ground squirrels (Spermophilus townsendii Merriam) in cool deserts increased the amount of spring recharge of soil moisture compared to areas without burrows. The objective of this study was to test the hypothesis that this additional soil moisture would enhance plant productivity. I compared productivity of western wheatgrass (Agropyron smithii Rydb.) and big sagebrush (Artemisia tridentata Nutt.) plants adjacent to burrows to plants in areas lacking burrows. Grass productivity was estimated within an experimental grid containing cells of either 0, 2, 4, or 6 artificial burrows and was based on measures of annual above ground biomass production and number of seed heads produced. For sagebrush, productivity was estimated from bushes without burrows (controls) and ones having a natural burrow near their base. Sagebrush productivity was based on average length of new annual terminal growth of vegetative stems. The mean annual estimates of grass biomass (50.0 g m-2 year-1, SE = 11.8) was significantly higher in test grid cells with the highest number of artificial burrows than controls (42.6 g m-2 year-1, SE = 11.4). The mean of annual estimates of sagebrush stem growth for bushes adjacent to burrows was a significant 0.6 cm (SE = 0.11) longer than bushes without burrows. I conclude that the added moisture from spring recharge at ground squirrel burrows can increase plant productivity in a cool desert environment.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202