Assessment of Olfactory Concealment Related to Habitat Selection by Terrestrial Animals

Animals use habitat selection to mitigate adverse effects environmental factors may have on their fitness. For many prey species, predation by olfactory-sensing predators is an environmental factor that has devastating impacts on their fitness. To minimize risk from olfactory-sensing predators, prey should select cover that reduces their odour cues that predators use to find them. The olfactory concealment theory predicts that this can be accomplished through selection of airflow characterized by high turbulence and/or updrafts. However, few studies have investigated airflow patterns as a dimension of cover. Here, I characterized the olfactory landscape, and assessed how olfaction relates to habitat selection and nest success of grassland-nesting birds. Specifically, I measured olfactory concealment and vegetation characteristics (e.g. visual concealment, grass height, etc.) within grassland, shrubland, and forest vegetation types and at nests in grassland vegetation. At a subset of points, I tested whether visual and/or olfactory concealment influenced depredation rates of simulated prey. Additionally, I modeled the relative importance of visual concealment, as well as airflow and weather conditions associated with olfactory concealment to nest survival. I found that turbulence intensity and airflow slope varied by vegetation type, and in grasslands horizontal concealment, vegetation height and vegetation roughness were positively correlated to turbulence intensity. Additionally, in grasslands turbulence intensity was the best predictor of simulated prey depredation. Together, these findings provide the first approximation of an olfactory landscape, which could potentially be used by animals to make space use decisions and in grasslands may be able to decrease rates of predator detection. However, contrary to expectations, grassland-nesting birds did not select nest sites with significantly higher levels of turbulence intensity (p=0.10), but did select more overhead visual concealment. A finding that I suspect reflects a habitat selection strategy to mitigate thermal conditions. Precipitation and humidity were important predictors of nest survival and were positively related. I hypothesize that moisture-related weather conditions indirectly influences nest survival through predation by olfactory-sensing predators. Findings here support those of others that weather can have a large impact on vital rates and that in some cases, habitat selection can potentially mitigate adverse effects of weather.Natural Resources and Ecology Managemen

Spatial patterns of woody plant encroachment in a temperate grassland

Context Woody encroachment is the process whereby grasslands transition to a woody-dominated state. This process is a global driver of grassland decline and is ultimately the outcome of increased woody plant recruitment in grasslands. Yet, little is known about how recruitment distances structure spatial patterns of encroachment. Objectives Here, we develop a recruitment curve to describe the scatter of woody plant recruitment around seed sources and examine how this structures spatial patterns of encroachment. Methods We developed a recruitment curve for Juniperus virginiana using an encroachment dataset that captures spread from tree plantings into treeless grassland sites in the Nebraska Sandhills (USA). In addition, we used height classes of encroaching J. virginiana as subsequent time steps of an encroachment process to examine how the leading edge of encroachment expanded over time. Results The recruitment curve was characterized by a fat-tailed distribution. Most recruitment occurred locally, within 157 m of seed sources (95th percentile distance), while, sparse long-distance recruitment characterized the curve’s tail. Expansion of the leading edge of encroachment was characterized by two features: (1) a slow moving, high density area near tree plantings and (2) rapid expansion of the distribution’s tail, driven by long-distance recruitment in treeless areas. Conclusion Our results show a high capacity for woody plant invasion of grasslands. Local recruitment drives transitions to woody dominance, while long-distance recruitment generates a rapidly advancing leading edge. Plans to conserve and restore grasslands will require spatially informed strategies that account for local and long-distance recruitment of woody plants

Spot-fire distance increases disproportionately for wildfires compared to prescribed fires as grasslands transition to \u3ci\u3eJuniperus\u3c/i\u3e woodlands

Woody encroachment is one of the greatest threats to grasslands globally, depleting a suite of ecosystem services, including forage production and grassland biodiversity. Recent evidence also suggests that woody encroachment increases wildfire danger, particularly in the Great Plains of North America, where highly volatile Juniperus spp. convert grasslands to an alternative woodland state. Spot-fire distances are a critical component of wildfire danger, describing the distance over which embers from one fire can cause a new fire ignition, potentially far away from fire suppression personnel. We assess changes in spot-fire distances as grasslands experience Juniperus encroachment to an alternative woodland state and how spot-fire distances differ under typical prescribed fire conditions compared to conditions observed during wildfire. We use BehavePlus to calculate spot-fire distances for these scenarios within the Loess Canyons Experimental Landscape, Nebraska, U.S.A., a 73,000-ha ecoregion where private-lands fire management is used to reduce woody encroachment and prevent further expansion of Juniperus fuels. We found prescribed fire used to control woody encroachment had lower maximum spot-fire distances compared to wildfires and, correspondingly, a lower amount of land area at risk to spot-fire occurrence. Under more extreme wildfire scenarios, spot-fire distances were 2 times higher in grasslands, and over 3 times higher in encroached grasslands and Juniperus woodlands compared to fires burned under prescribed fire conditions. Maximum spot-fire distance was 450% greater in Juniperus woodlands compared to grasslands and exposed an additional 14,000 ha of receptive fuels, on average, to spot-fire occurrence within the Loess Canyons Experimental Landscape. This study demonstrates that woody encroachment drastically increases risks associated with wildfire, and that spot fire distances associated with woody encroachment are much lower in prescribed fires used to control woody encroachment compared to wildfires

Influence of olfactory and visual cover on nest site selection and nest success for grassland-nesting birds

Habitat selection by animals is influenced by and mitigates the effects of predation and environmental extremes. For birds, nest site selection is crucial to offspring production because nests are exposed to extreme weather and predation pressure. Predators that forage using olfaction often dominate nest predator communities; therefore, factors that influence olfactory detection (e.g., airflow and weather variables, including turbulence and moisture) should influence nest site selection and survival. However, few studies have assessed the importance of olfactory cover for habitat selection and survival. We assessed whether ground‐nesting birds select nest sites based on visual and/or olfactory cover. Additionally, we assessed the importance of visual cover and airflow and weather variables associated with olfactory cover in influencing nest survival. In managed grasslands in Oklahoma, USA, we monitored nests of Northern Bobwhite (Colinus virginianus), Eastern Meadowlark (Sturnella magna), and Grasshopper Sparrow (Ammodramus savannarum) during 2015 and 2016. To assess nest site selection, we compared cover variables between nests and random points. To assess factors influencing nest survival, we used visual cover and olfactory‐related measurements (i.e., airflow and weather variables) to model daily nest survival. For nest site selection, nest sites had greater overhead visual cover than random points, but no other significant differences were found. Weather variables hypothesized to influence olfactory detection, specifically precipitation and relative humidity, were the best predictors of and were positively related to daily nest survival. Selection for overhead cover likely contributed to mitigation of thermal extremes and possibly reduced detectability of nests. For daily nest survival, we hypothesize that major nest predators focused on prey other than the monitored species’ nests during high moisture conditions, thus increasing nest survival on these days. Our study highlights how mechanistic approaches to studying cover informs which dimensions are perceived and selected by animals and which dimensions confer fitness‐related benefits.Peer reviewedNatural Resource Ecology and Managemen

Heterogeneity

This entry discusses heterogeneity in the context of ecological landscapes and how the heterogeneity impacts the resilience of the system. Heterogeneity is closely linked to the scale of measurement, both spatially and temporally. We will walk through a simple example that highlights how the scale of observation can impact the heterogeneity of the system. The differences between functional and measured heterogeneity will also be explained. Finally, heterogeneity will be discussed in the context of its utility to management and how it can be used to understand the resilience of agro-ecosystems. Overview - What Will You Learn In This Lesson? This lesson discusses what heterogeneity is and how it relates to understanding and interpreting natural phenomena. Objectives This lesson covers the concept of heterogeneity. At the end of this module you should be able to: Define heterogeneity in the context of environmental management Explain the relationship between heterogeneity and ecological resilience Differentiate between functional and measured heterogeneity in ecology Understand the importance and usefulness of heterogeneity in resource management Modules Lesson home Overview and Objectives Introduction - What Is Heterogeneity? Measures of Heterogeneity Heterogeneity in Management - How Does This Concept Impact Real-World Management? Example - Heterogeneity of Zoning in Cities Summary - What Did We Learn? Quiz Questions References and Further Reading Glossar

Rangelands in a fragmented grass‑dominated landscape are vulnerable to tree invasion from roadsides

Roadsides can be vectors for tree invasion within rangelands by bisecting landscapes and facilitating propagule spread to interior habitat. Current invasive tree management in North America’s Great Plains focuses on reducing on-site (i.e., interior habitat) vulnerability through on-site prevention and eradication, but invasive tree management of surrounding areas known to serve as invasion vectors, such as roadsides and public rights-of-ways, is sporadic. We surveyed roadsides for invasive tree propagule sources in a central Great Plains grassland landscape to determine how much of the surrounding landscape is potentially vulnerable to roadside invasion, and by which species, and thereby provide insights into the locations and forms of future landcover change. Invasive tree species were widespread in roadsides. Given modest seed dispersal distances of 100–200 m, our results show that roadsides have potential to serve as major sources of rangeland exposure to tree invasion, compromising up to 44% of rangelands in the study area. Under these dispersal distances, funds spent removing trees on rangeland properties may have little impact on the landscape’s overall vulnerability, due to exposure driven by roadside propagule sources. A key implication from this study is that roadsides, while often neglected from management, represent an important component of integrated management strategies for reducing rangeland vulnerability to tree invasion

Impact of Eastern Redcedar Proliferation on Water Resources in the Great Plains USA—Current State of Knowledge

In the Great Plains of the central United States, water resources for human and aquatic life rely primarily on surface runoff and local recharge from rangelands that are under rapid transformation to woodland by the encroachment of Eastern redcedar (redcedar; Juniperus virginiana) trees. In this synthesis, the current understanding and impact of redcedar encroachment on the water budget and water resources available for non-ecosystem use are reviewed. Existing studies concluded that the conversion from herbaceous-dominated rangeland to redcedar woodland increases precipitation loss to canopy interception and vegetation transpiration. The decrease of soil moisture, particularly for the subsurface soil layer, is widely documented. The depletion of soil moisture is directly related to the observed decrease in surface runoff, and the potential of deep recharge for redcedar encroached watersheds. Model simulations suggest that complete conversion of the rangelands to redcedar woodland at the watershed and basin scale in the South-central Great Plains would lead to reduced streamflow throughout the year, with the reductions of streamflow between 20 to 40% depending on the aridity of the climate of the watershed. Recommended topics for future studies include: (i) The spatial dynamics of redcedar proliferation and its impact on water budget across a regional hydrologic network; (ii) the temporal dynamics of precipitation interception by the herbaceous canopy; (iii) the impact of redcedar infilling into deciduous forests such as the Cross Timbers and its impact on water budget and water availability for non-ecosystem use; (iv) land surface and climate interaction and cross-scale hydrological modeling and forecasting; (v) impact of redcedar encroachment on sediment production and water quality; and (vi) assessment and efficacy of different redcedar control measures in restoring hydrological functions of watershed

Next-generation technologies unlock new possibilities to track rangeland productivity and quantify multi-scale conservation outcomes

Historically, relying on plot-level inventories impeded our ability to quantify large-scale change in plant biomass, a key indicator of conservation practice outcomes in rangeland systems. Recent technological advances enable assessment at scales appropriate to inform management by providing spatially comprehensive estimates of productivity that are partitioned by plant functional group across all contiguous US rangelands. We partnered with the Sage Grouse and Lesser Prairie-Chicken Initiatives and the Nebraska Natural Legacy Project to demonstrate the ability of these new datasets to quantify multi-scale changes and heterogeneity in plant biomass following mechanical tree removal, prescribed fire, and prescribed grazing. In Oregon’s sagebrush steppe, for example, juniper tree removal resulted in a 21% increase in one pasture’s productivity and an 18% decline in another. In Nebraska’s Loess Canyons, perennial grass productivity initially declined 80% at sites invaded by trees that were prescriptively burned, but then fully recovered post-fire, representing a 492% increase from nadir. In Kansas’ Shortgrass Prairie, plant biomass increased 4-fold (966,809 kg/ha) in pastures that were prescriptively grazed, with gains highly dependent upon precipitation as evidenced by sensitivity of remotely sensed estimates (SD ± 951,308 kg/ha). Our results emphasize that next-generation remote sensing datasets empower land managers to move beyond simplistic control versus treatment study designs to explore nuances in plant biomass in unprecedented ways. The products of new remote sensing technologies also accelerate adaptive management and help communicate wildlife and livestock forage benefits from management to diverse stakeholders

A Biome in Transition: Co-Produced Science for Grassland Conservation

Confronting biome-scale threats in the 21st century will require new and adaptive approaches for conservation. The overarching theme of this dissertation is co-produced science for the conservation of grasslands threatened by woody encroachment. Each chapter reflects a research question co-developed by scientists and managers to better understand and manage the threat of woody encroachment. First, I examine the dimensions of grassland risk through a series of field studies. Risk is the outcome of a grassland’s sensitivity and exposure to encroaching woody plants. Sensitivity reflects the rate and ease of grassland transition to a woodland, while, exposure is driven by propagule sources and their dispersal. My findings demonstrate the importance of exposure in driving patterns of encroachment and provide a basis for managing the spatial dimensions of exposure. Second, I assess the potential impacts of plant invasions in grasslands using a participatory ecosystem service assessment. Findings illustrate the potential for severe impacts associated with woodland transitions driven by a native invasive tree compared to non-native invasive weeds. Third, I assess the sustainability of grassland conservation approaches, including the lifespan of restoration treatments. Overall, I find unsustainable trends of grassland loss to encroachment across a network of priority conservation areas. Conservation efforts tended to be outpaced by encroachment of intact grasslands and re-encroachment of sites undergoing restoration, which rapidly transition back to a woodland without follow-up management. Large-scale fire management provided the only example of counteracting regional trends of encroachment and serves as a model for improving conservation efforts in other grasslands threatened by encroachment. However, the viability of this approach will likely depend upon broader acceptance of the role of prescribed fire in grasslands. To this end, I developed fire management scenarios to contrast air-quality outcomes of large-scale fire management versus those of fire exclusion. The scenarios illustrate the inevitable nature of fire in flammable ecosystems and provide a basis for communicating the role of prescribed fire in avoiding long-term consequences associated with wildfire