Shawn M. Crimmins

Changes in Climatic Water Balance Drive Downhill Shifts in Plant Species' Optimum Elevations

Many mountain plant species in California shifted downhill, tracking regional changes in water balance. Uphill shifts of species’ distributions in response to historical warming are well documented, which leads to widespread expectations of continued uphill shifts under future warming. Conversely, downhill shifts are often considered anomalous and unrelated to climate change. By comparing the altitudinal distributions of 64 plant species between the 1930s and the present day within California, we show that climate changes have resulted in a significant downward shift in species’ optimum elevations. This downhill shift is counter to what would be expected given 20th-century warming but is readily explained by species’ niche tracking of regional changes in climatic water balance rather than temperature. Similar downhill shifts can be expected to occur where future climate change scenarios project increases in water availability that outpace evaporative demand.

Modeling plant ranges over 75 years of climate change in California, USA: temporal transferability and species traits

Species distribution model (SDM) projections under future climate scenarios are increasingly being used to inform resource management and conservation strategies. A critical assumption for projecting climate change responses is that SDMs are transferable through time, an assumption that is largely untested because investigators often lack temporally independent data for assessing transferability. Further, understanding how the ecology of species influences temporal transferability is critical yet almost wholly lacking. This raises two questions. (1) Are SDM projections transferable in time? (2) Does temporal transferability relate to species ecological traits? To address these questions we developed SDMs for 133 vascular plant species using data from the mountain ranges of California (USA) from two time periods: the 1930s and the present day. We forecast historical models over 75 years of measured climate change and assessed their projections against current distributions. Similarly, we hindcast contemporary models and compared their projections to historical data. We quantified transferability and related it to species ecological traits including physiognomy, endemism, dispersal capacity, fire adaptation, and commonness. We found that non-endemic species with greater dispersal capacity, intermediate levels of prevalence, and little fire adaptation had higher transferability than endemic species with limited dispersal capacity that rely on fire for reproduction. We demonstrate that variability in model performance was driven principally by differences among species as compared to model algorithms or time period of model calibration. Further, our results suggest that the traits correlated with prediction accuracy in a single time period may not be related to transferability between time periods. Our findings provide a priori guidance for the suitability of SDM as an approach for forecasting climate change responses for certain taxa.

Bobcat Population Status and Management in North America: Evidence of Large-Scale Population Increase

Abstract Bobcat Lynx rufus populations are thought to be increasing in North America; however, little information exists on their current population status. In the United States, management and mon...

Browsing Patterns of White-Tailed Deer Following Increased Timber Harvest and a Decline in Population Density

We examined browsing patterns of white-tailed deer (Odocoileus virginianus) on a site in the central Appalachians that experienced a substantial (>50%) reduction in deer population density and an increase in the amount of timber harvest since 2001. We sampled woody browse in and immediately adjacent to 12 clearcuts ranging in age from 0–5 years postharvest in summer 2007. Clearcut-interior areas had higher woody browse abundance and browsing rates than clearcut-edge or mature forest areas. Woody browse abundance was slightly higher within individual clearcuts than in 2001 at higher population densities and lower timber harvest rates. Overall browsing rates declined from approximately 17% in 2001 to less than 5% during our study, suggesting that the combination of deer population control, and increasing the amount of timber harvest across the landscape can reduce herbivory to levels that may not impede growth and survival of forest vegetation.

Canis latrans (Coyote) Habitat Use and Feeding Habits in Central West Virginia

Abstract Canis latrans (Coyote) populations are expanding throughout the eastern United States, making them the apex predator in many systems. Despite abundant research in the western United States, relatively little information exists on the space use or feeding patterns of Coyotes in the forested landscapes of the Appalachians. We used radio-telemetry and scat analysis to describe seasonal habitat use and feeding patterns of Coyotes in central West Virginia during 2006–2008. Odocoileus virginianus (White-tailed Deer) was the most common prey, occurring in 76% of scats collected in winter and 45% of scats collected in summer. Rodents were the most common prey item in summer, occurring in 48% of scats; other prey items occurred in <20% of scats. Coyotes selected for recently harvested forest stands while avoiding intact stands in both summer and winter. Despite exhibiting seasonal prey-switching behavior, Coyotes in this region do not alter habitat-use patterns with respect to season. Coyotes in our study seem to be opportunistic feeders that prefer areas with abundant cover. Their opportunistic feeding patterns may contribute to their rapid population expansion in this region.

Effects of Prey Size on Scat Analysis to Determine River Otter Lontra canadensis Diet

We conducted a controlled feeding trial using two captive river otters Lontra canadensis to determine how prey size may introduce bias into frequency of occurrence analysis using otter scats. Otters were fed specific prey across a range of sizes. We then collected all scats deposited by the otters to determine how many defecation events occurred to remove the prey item from the digestive system. We found a strong, positive relationship between prey item size and the number of scats required to excrete the item. We then examined how the results, of an actual river otter feeding habits study using frequency of occurrence analysis of scats, could be biased towards an over-representation of larger prey items by using a correction factor for prey item size developed from our feeding trials. Frequency of occurrence suggested a strong preference for mid-range size of prey items and a strong avoidance of smaller prey items. Our corrected results indicated that otters exhibit little preferential feeding based on prey item size in the Missouri Ozarks. Our results suggest that bias associated with frequency of occurrence analyses may severely limit the robustness of inferences that can be made from such analyses.

An Evaluation of Bridge-Sign Surveys to Monitor River Otter (Lontra Canadensis) Populations

ABSTRACT Monitoring animal populations is critical for the development of successful management strategies. This is especially important for populations that have been reintroduced to historic habitats, such as river otters (Lontra canadensis), which were reintroduced to Missouri during the 1980s and 1990s. We measured river otter relative abundance in southern Missouri using seasonal bridge-sign surveys on 15 study areas from 1996 to 1999. Otter sign was detected at 63% of the bridges during fall surveys and 82% of the bridges during spring surveys. Relative abundance during the fall 1996 survey (the only pre-harvest survey) was significantly higher (P  =  0.0014) than during the fall 1997 and fall 1998 surveys that followed the institution of a legal trapping season. Relative abundance based on spring surveys were not significantly different (P  =  0.196) over the 3 y. Repeat surveys conducted in the same year did not result in significantly different relative abundance in either fall 1997 (P  =  0.13) or spring 1997 (P  =  0.27). These results were similar to catch per unit effort (CPUE) estimates, but not entirely consistent. We recommend that managers conduct bridge-sign surveys during the same season and employ at least one other direct measure of the relative abundance (CPUE or mark-recapture) in order to monitor long-term relative abundance of otters.

Do Trends in Muskrat Harvest Indicate Widespread Population Declines

Abstract Ondatra zibethicus (Muskrat) is one of the most widely distributed furbearers in eastern North America. Anecdotal evidence suggests that Muskrats are experiencing a regional decline in numbers, although little empirical evidence exists to support this claim. Our objectives were to document temporal trends in Muskrat harvest in eastern North America, and to use the relationship between harvest and pelt price to infer potential trends in regional Muskrat populations. Muskrat harvest has declined by approximately 75% since 1986 in eastern North America, despite a recent resurgence in pelt prices. Recent harvest rates showed little correlation (r2 = 0.355-0.559) with current or time-lagged pelt prices, despite large correlations (r2= 0.785-0.823) between pelt price and harvest from historic data (1948–1968). These results suggest that, at low harvest levels, there is only a weak correlation between harvest and pelt price. These results may be indicative of regional declines in Muskrat abundance, although future research is needed to substantiate this hypothesis.

Age-Specific Reproductive Rates of River Otters in Southern Missouri

Abstract Sustained reproduction is critical for successful restoration of extirpated populations. Evaluating success of restoration efforts requires an understanding of reproductive capacity in such populations. We examined age-specific reproductive capacity of a Lontra canadensis (River Otter) population in southern Missouri that was the focus of intense restoration efforts in the 1980s and early 1990s. We collected carcasses of 387 legally harvested female Otters from 1996–1999. Otters ranged in age from 1–11 years, with juveniles (<1 yr) the dominant (41.1%) age class. Mean annual corpora lutea counts were high ( = 2.48 ± 0.12) and present in 72.8% of adult (>1 yr) Otters. Our results indicate that the southern Missouri River Otter population has one of the greatest recorded potential reproductive capacities for that species.

Responses of Female White-tailed Deer Home-Ranges to Increased Resource Availability

Abstract Management strategies designed to reduce the negative impacts of overabundant Odocoileus virginianus (White-tailed Deer) populations on forest regeneration may be influenced by changes in both population density and timber harvest. However, there is conflicting evidence as to how such changes in per capita resource availability influence home-range patterns. We compared home-range patterns of 33 female White-tailed Deer from a low-density population at a site with abundant browse to patterns of a sample of >100 females prior to a 75% reduction in population density and a doubling in timber harvest area. Home-range and core-area sizes were approximately 3 times larger than were found prior to population decline and timber harvest increase, consistent with predictions related to intraspecific competition. We also observed greater site fidelity than previously exhibited, although this may be an artifact of increased home-range sizes. Our results support previous research suggesting that White-tailed Deer home-range size is inversely related to population density and is driven, in part, by intraspecific competition for resources. Relationships among population density, resource availability, and home-range patterns among female White-tailed Deer appear to be complex and context specific.