Soil and vegetation differences across ecological boundaries in an arid South African ecosystem

Boundaries are the most reactive nodes in landscapes and may be hypersensitive to global change in climate and land use. Investigations on how soils govern vegetation boundaries are scant, particularly in arid and semiarid ecosystems. The Tankwa Karoo National Park (TKNP) is a unique arid biodiversity hotspot with an unrivalled aridity gradient from < 100 mm MAP to about 700 mm in < 10 km. We investigated the abruptness of four soil‐vegetation boundaries separating eight communities. Two 50 m transects were established across four boundaries for 24 descending point transects, in which the cover‐abundance of each plant encounter at 1 m intervals was recorded. In addition, three soil samples were collected from the top 5 cm in each of the four boundaries and twelve patches. Soil and vegetation parameters altogether indicated three boundary syndromes that were context dependent: (a) a sharp boundary, (b) a gradual boundary or (c) no boundary exists. Soil respiration recorded here, and perhaps other ecosystem processes, was mediated by the soil‐vegetation boundaries. These nodes should be the focus of ecological studies since they reveal much more than the constituent patches themselves.     

Occupancy and detectability of Snowy Plovers in western Utah: an application to a low density population

Occupancy modeling can be used to identify habitat characteristics associated with species occurrence. Additionally, occupancy sampling can provide measures of detection probability, increasing confidence in monitoring efforts. Little is known about the distribution and habitat preferences of a small population of Snowy Plovers (Charadrius nivosus) in western Utah. We conducted a study to estimate occupancy and detection probability of Snowy Plovers in western Utah during 2011 and 2012. We made repeated visits to randomly selected survey plots during the breeding period, sampling 84 64‐ha plots in 2011 and 100 64‐ha plots in 2012 and recording the number of adults and habitat characteristics in each plot. We then modeled the relationship between detection, occupancy, and covariates that included distance to water, distance to roads, land cover types, and characteristics of the vegetation. We also included covariates for observer, Julian date, temperature, cloud cover, and wind speed when modeling detection probability. Detection probability was high (0.74, 95% CI = 0.57–0.86) and positively influenced by temperature. Occupancy of 64‐ha plots was low (0.27, 95% CI = 0.18–0.39) and did not vary by year. Occupancy of Snowy Plovers was negatively associated with distance to water (β = ?0.62 ± 0.31, 95% CI = ?1.23 to ?0.01) and percent shrub cover (β = ?0.28 ± 0.02, 95% CI = ?0.58 to ?0.01). Land cover types also influenced plot occupancy. Management actions that conserve shallow water and adjacent habitats or minimize disturbance in these areas are likely to have conservation benefits for Snowy Plovers where water is scarce. Because our detection probabilities were high, investigators involved in future monitoring efforts can achieve reasonable precision with limited revisits to sample plots.     

Black Bear Movement and Food Conditioning in an Exurban Landscape

Conflicts between humans and wildlife have become increasingly important challenges for resource managers along the urban-wildland interface. Food conditioning (i.e., reliance by an animal on anthropogenic foods) of American black bears (Ursus americanus) is related to conflict behavior (i.e., being bold or aggressive toward humans, consuming human food or garbage, causing property damage) and often occurs in communities adjacent to Great Smoky Mountains National Park (GRSM or Park), USA. The goal of our study was to evaluate black bear space use in GRSM and in exurban areas on surrounding private lands and to identify factors associated with food conditioning and conflict behavior. We radio-collared 53 bears (29 males, 24 females) from 2015 to 2017 to compare space use characteristics and used carbon isotopic signatures (δ¹³C) from bear hair to assess food conditioning. We then performed an integrated step selection function (iSSF) analysis to characterize and compare movement and resource use as related to food conditioning. Based on the stable isotope analyses, 24 bears were classified as food conditioned (FC; 16 males and 8 females) and 37 were not food conditioned (NFC; 14 males and 23 females). Annual 95% kernel density estimate (KDE) home ranges and 50% KDE core area estimates of female and male bears did not differ by level of food conditioning (i.e., mean δ¹³C), but 95% and 50% home ranges of FC females were smaller than NFC females when data from 2015, a year of food scarcity and abnormally large home ranges, were excluded. The mean proportion of exurban development (e.g., roads, buildings, openings) within 95% KDE and 50% KDE home ranges of females increased with mean δ¹³C (i.e., greater food conditioning). The iSSF models indicated that FC bears were more likely to use forest openings associated with higher levels of development than NFC bears. We used those models to demonstrate how landscape modifications can reduce bear use of exurban areas, particularly for NFC bears. Our stable isotope, movement, and resource use data indicate that conflict behaviors displayed by many bears within GRSM were learned in areas outside Park boundaries. © 2020 The Wildlife Society.     

A new cost‐distance model for human accessibility and an evaluation of accessibility bias in permanent vegetation plots in Great Smoky Mountains National Park,USA

Question: Can a new cost‐distance model help us to evaluate the potential for accessibility bias in ecological observations? How much accessibility bias is present in the vegetation monitoring plots accumulated over the last three decades in Great Smoky Mountains National Park? Location: Great Smoky Mountains National Park, North Carolina and Tennessee, USA. Methods: Distance, slope, stream crossings, and vegetation density were incorporated into a least‐cost model of energetic expenditure for human access to locations. Results: Estimated round‐trip energy costs for the park ranged from 0 to 1.62 × 10⁵ J kg^?1. The estimated round‐trip energetic expenditure for the surveys ranged from 53 to 1.51 × 10⁵ J kg^?1. Their distribution was more accessible than the random expectation. Ten (17%) of the vegetation types in the park are significantly under‐sampled relative to their area, and 16 (29%) are over‐sampled. Plots in 18 of the 40 vegetation types exhibited a significant positive correlation with accessibility. Conclusions: The least‐cost model is an improvement over previous attempts to quantify accessibility. The bias in plot locations suggests using a least‐cost model to test for bias in cases in which human accessibility is confounded with other sources of ecosystem variation.     

Effects of changing climate on aquatic habitat and connectivity for remnant populations of a wide‐ranging frog species in an arid landscape

Amphibian species persisting in isolated streams and wetlands in desert environments can be susceptible to low connectivity, genetic isolation, and climate changes. We evaluated the past (1900–1930), recent (1981–2010), and future (2071–2100) climate suitability of the arid Great Basin (USA) for the Columbia spotted frog (Rana luteiventris) and assessed whether changes in surface water may affect connectivity for remaining populations. We developed a predictive model of current climate suitability and used it to predict the historic and future distribution of suitable climates. We then modeled changes in surface water availability at each time period. Finally, we quantified connectivity among existing populations on the basis of hydrology and correlated it with interpopulation genetic distance. We found that the area of the Great Basin with suitable climate conditions has declined by approximately 49% over the last century and will likely continue to decline under future climate scenarios. Climate conditions at currently occupied locations have been relatively stable over the last century, which may explain persistence at these sites. However, future climates at these currently occupied locations are predicted to become warmer throughout the year and drier during the frog's activity period (May – September). Fall and winter precipitation may increase, but as rain instead of snow. Earlier runoff and lower summer base flows may reduce connectivity between neighboring populations, which is already limited. Many of these changes could have negative effects on remaining populations over the next 50–80 years, but milder winters, longer growing seasons, and wetter falls might positively affect survival and dispersal. Collectively, however, seasonal shifts in temperature, precipitation, and stream flow patterns could reduce habitat suitability and connectivity for frogs and possibly other aquatic species inhabiting streams in this arid region.