Deer Abundance Research Articles

Assessing precision and requirements of three methods to estimate roe deer density.

Roe deer (Capreolus capreolus) is the most abundant cervid in Europe and, as such, has a considerable impact over several human activities. Accurate roe deer population size estimates are useful to ensure their proper management. We tested 3 methods for estimating roe deer abundance (drive counts, pellet-group counts, and camera trapping) during two consecutive years (2012 and 2013) in the Apennines (Italy) in order to assess their precision and applicability. During the study period, population density estimates were: drive counts 21.89±12.74 roe deer/km2 and pellet-group counts 18.74±2.31 roe deer/km2 in 2012; drive counts 19.32±11.12 roe deer/km2 and camera trapping 29.05±7.48 roe deer/km2 in 2013. Precision of the density estimates differed widely among the 3 methods, with coefficients of variation ranging from 12% (pellet-group counts) to 58% (drive counts). Drive counts represented the most demanding method on account of the higher number of operators involved. Pellet-group counts yielded the most precise results and required a smaller number of operators, though the sampling effort was considerable. When compared to the other two methods, camera trapping resulted in an intermediate level of precision and required the lowest sampling effort. We also discussed field protocols of each method, considering that volunteers, rather than technicians, will more likely be appointed for these tasks in the near future. For this reason, we strongly suggest that for each method managers of population density monitoring projects take into account ease of use as well as the quality of the results obtained and the resources required.

HABITAT USE AND DIET OF DESERT BIGHORN SHEEP (OVIS CANADENSIS MEXICANA) AND ENDEMIC MULE DEER (ODOCOILEUS HEMIONUS NELSONII) ON TIBURÓN ISLAND, MEXICO

In 1975, wildlife managers reintroduced desert bighorn sheep (Ovis canadensis mexicana) to Tiburon Island, Mexico, where endemic mule deer (Odocoileus hemionus sheldoni) occur. We predicted that these species would use both mountain and plains habitats, but would have different diets, minimizing negative interspecific effects. By censusing pellet groups, we found that both ungulates occurred in both habitats, but bighorn sheep were more abundant in mountains and mule deer were more abundant in plains. Microhistological analyses determined that diets of both species consisted of the same 39 plant species, of which 13 plant species each composed ≥4% of the diet and together composed 70–80% of the total diet. Plants in low abundance represented 26–32% of diets in the mountains and 45–56% of diets in the plains. Overall diet overlap was 68% and overlap did not differ between mountains or plains, but did differ among seasons. Overlap in habitat agreed with predictions, but diet overlap was contrary to our predictions. Our results differ from studies on the mainland, which found overlap in habitat use, but not in diet. Overlap in resource use coupled with the rapid increase in abundance of bighorn sheep since their reintroduction to Tiburon may have an impact on mule deer. Additional research is needed to determine whether abundance of mule deer has changed in response to the reintroduction of bighorn sheep.

Climate, competition and weather conditions drive vertical displacement and habitat use of an alpine ungulate in a highly topographic landscape

Many species experience ecosystem changes due to alterations in climate or interspecific interactions. Animals’ optimal use of landscapes involves adjusting spatial displacement and habitat use according to weather or climate, however, competitive interactions may affect such behavioural responses. Species in alpine landscapes are already at their upper altitudinal range, which can limit behavioural response to ecosystem changes. We investigated how ibex’s use of habitat and altitude was affected by weather, climate, and intra- and interspecific competition in an alpine landscape in Switzerland. We combined data from GPS-collared ibex with data on temperature and precipitation, habitat and altitude, and abundance estimates of ibex, chamois, and red deer within the study area. We modelled how the temporal dynamics of habitat and altitude use by ibex was modified by weather, ungulate abundance, and their interactions. Short- and long-term weather conditions affected ibex’s use of landscape throughout the year as expected based on its ecology, with particularly strong effects of temperature during spring and summer. During spring and autumn, ibex used higher altitudes and less grassland when red deer abundance was high and ibex abundance low. The influence of weather and climate on how ibex used the landscape was only weakly affected by interspecific competition. Our results suggest that the way that ibex use the landscape is affected by environmental conditions and intra- and interspecific interactions. These factors seem to have additive effects on ibex behaviour.

Effects of white-tailed deer (Odocoileus virginianus) exclusion on plant recovery in overwash fans after a severe coastal storm.

We documented the impacts of an abundant deer population on dune vegetation recovering from severe storm surge on a barrier island through use of permanent plots and a repeated measures analysis. Three years after landfall of the storm, vegetation cover was dominated by American beachgrass, Ammophila breviligulata, though we observed 12 plant species among plots surveyed. We documented significantly greater vegetation cover in fenced than unfenced plots in overwash fans in two consecutive years. The difference in species richness between fenced and unfenced plots was significant, though richness was consistently low (≤4 species per plot) and we did not detect a statistically significant difference between years. Both deer trampling and foraging effects were captured in this study, though separation between these effects was not possible. Because trampling effects are often exacerbated on sandy soils, trampling and foraging effects should be isolated and investigated in future assessments of deer impacts on coastal vegetation. Managing deer to lower abundance may enhance coastal resilience if vegetation is allowed to recover unimpeded by foraging and trampling, though a better understanding of the precise nature of deer impacts on dune vegetation is necessary.

Conservation Reserve Program is a key element for managing white-tailed deer populations at multiple spatial scales

Understanding the underlying mechanisms driving population demographics such as species-habitat relationships and the spatial scale in which these relationships occur is essential for developing optimal management strategies. Here we evaluated how landscape characteristics and winter severity measured at three spatial scales (1 km2, 9 km2, and hunting unit) influenced white-tailed deer occurrence and abundance across North Dakota by using 10 years of winter aerial survey data and generalized linear mixed effects models. In general, forest, wetland, and Conservation Reserve Program (CRP) lands were the main drivers of deer occurrence and abundance in most of the spatial scales analyzed. However, the effects of habitat features vary between the home-range scale (9 km2) and the finer spatial scale (1 km2; i.e., within home ranges). While escape cover was the main factor driving white-tailed deer occurrence and abundance at broad spatial scales, at a fine spatial scale deer also selected for food (mainly residual winter cropland). With CRP appearing in nearly all top models, here we had strong evidence that this type of program will be fundamental to sustaining populations of white-tailed deer that can meet recreational demands. In addition, land managers should focus on ways to protect other escape covers (e.g., forest and wetland) on a broad spatial scale while encouraging landowners to supply winter resources at finer spatial scales. We therefore suggest a spatial multi-scale approach that involves partnerships among landowners and government agencies for effectively managing white-tailed deer.

Using spotlight observations to predict resource selection and abundance for white‐tailed deer

ABSTRACTSpotlight surveys for white‐tailed deer (Odocoileus virginianus) can yield large presence‐only datasets applicable to a variety of resource selection modeling procedures. By understanding how populations distribute according to a given resource for a reference area, density and abundance can be predicted across new areas assuming the relationship between habitat quality (measured by an index of selection) and species distribution are equivalent. Habitat‐based density estimators have been applied to wildlife species and are useful for addressing conservation and management concerns. Although achieving reliable population estimates is a primary goal for spotlighting studies, presence‐only models have yet to be applied to spotlight data for estimating habitat selection and abundance for deer. From 2012 to 2017, we conducted spring spotlight surveys in each of 99 counties in Iowa, USA, and collected spatial locations for 20,149 groups of deer (n = 71,323 individuals). We used a resource selection function (RSF) based on deer locations to predict the relative probability of use for deer at the population level and to estimate statewide abundance. The number of deer observed statewide increased significantly with increasing RSF value for all years and the mean RSF value along survey transects explained 59% of the variability in county‐level deer counts, indicating that a functional response between habitat quality and deer distribution existed at landscape scales. We applied our RSF to a habitat‐based density estimator (extrapolation) and zero‐inflated Poisson (ZIP) and negative binomial (ZINB) count models to predict statewide abundance from spotlight counts. Population estimates for 2012 were variable, indicating that atypical weather conditions may affect spotlight counts and population estimates in some years. For 2013–2017, we predicted a mean population of 439,129 (95% CI ∼ ± 55,926), 440,360 (∼ ± 43,676), and 465,959 (∼ ± 51,242) deer across years for extrapolation, ZIP, and ZINB models, respectively. Estimates from all models were not significantly different than estimates from an existing deer population accounting model in Iowa for 2013 and 2016, and differed by <76,000 deer for all models from 2013–2017. Extrapolation and ZIP models performed similarly and differed by <2,897 deer across all years, whereas ZINB models showed inconsistencies in model convergence and precision of estimates. Our results indicate that presence‐only models are capable of producing reliable and precise estimates of resource selection and abundance for deer at broad landscape scales in Iowa and provide a tool for estimating deer abundance in a spatially explicit manner. © 2019 The Wildlife Society.

Changes in host densities and co-feeding pattern efficiently predict tick-borne encephalitis hazard in an endemic focus in northern Italy

Tick-borne encephalitis is an important zoonosis in many parts of north-western, central and eastern Europe, Russia and the Far East, with considerable altitudinal and latitudinal shifts described during recent decades. The reported routes of transmission for TBE virus include the saliva-activated non-viraemic transmission between co-feeding ticks taking place on rodent hosts. During the period 2001–2014, a population of the yellow-necked mouse (Apodemus flavicollis), which is considered among the most efficient TBE competent host, especially in central and western Europe, was intensively live-trapped in a known TBE focus in the Province of Trento, Italy. Individual live-trapped mice were checked for the number and position of feeding ticks and serologically screened for TBEv antibodies. A combined effect of climatic conditions and density of both roe deer and mice on the number of co-feeding tick groups was observed. Specifically, the occurrence of co-feeding ticks on mice during the questing season was affected by autumnal cooling in the previous season. On the other hand, co-feeding occurrence was also positively associated with roe deer abundance, while mouse density showed a hump-shaped pattern. Individual features of A. flavicollis such as weight and sex also affected co-feeding occurrence with the heaviest (breeding adult) males carrying more co-feeding ticks. We also found that the overall number of co-feeding ticks on mice positively affected TBEv antibody detection in this species the following year. In conclusion, a specific combination of climatic conditions in conjunction with certain rodent and roe deer densities are the principal determinants of the number of co-feeding ticks on A. flavicollis and, consequently, TBEv circulation. These variables can be used to provide an early warning signal for a TBE hazard, thus representing a useful tool for Public Health authorities to prepare action for prevention and control within TBEv circulation areas.

Abundance and Density of a Columbian Black-Tailed Deer Population on an Urban Island

Methods to estimate abundance and density of Columbian black-tailed deer (Odocoileus hemionus columbianus) are limited. Regional wildlife managers are concerned that Columbian black-tailed deer on Whidbey Island, Washington, USA, exceed carrying capacity. Research on small islands in the Pacific Northwest reports high deer densities; however, these islands are smaller and less complex than Whidbey Island, and have fewer mortality sources. Our objective was to estimate the abundance and density of Columbian black-tailed deer on Whidbey Island by using road-based spotlight surveys in a distance sampling framework. We conducted spotlight surveys from 12 January 2015 to 23 January 2015 starting ≤1 h after sunset and continuing to 23:00. The deer population of Whidbey Island is estimated to be 2744.5 individuals (6.2 deer/km2), lower than estimated densities of deer on smaller islands in the region. Density varied across the different sections of Whidbey Island. Road-based spotlight surveys in a distance sampling framework are a useful tool for estimating deer populations in regions where traditional monitoring methods are not practical. This research offers baseline estimates for the deer on Whidbey Island and provides a repeatable procedure to estimate abundance and density.

Long‐term dynamics of Alpine ungulates suggest interspecific competition

AbstractStudies identifying interspecific competition require the investigation of negative long‐term effects between sympatric species showing overlap in resource use. A potential for competition exists between red deer Cervus elaphus and chamois Rupicapra spp., as revealed by the high dietary overlap observed throughout the range where the species co‐occur. Furthermore, some studies have recently reported negative demographic consequences on chamois populations living in sympatry with red deer. Using time series of counts spanning 35 years between 1984 and 2018 in the Stelvio National Park (Central Italian Alps), we tested for density dependence using state‐space models and explored the evidence of competitive interaction through Ricker‐like models on the growth rate of both species. We contrasted alternative hypotheses for the processes explaining the trends of (decreasing) chamois and (increasing) red deer populations. We expected chamois dynamics to be negatively affected by increasing deer abundance, while deer dynamics should be primarily affected by climate forcing and density dependence. We found evidence that resources were limiting for both species. In particular, growth rates were negatively affected by the synergistic effect of winter weather conditions and density dependence. The most important variable limiting the chamois population, however, was the increase in red deer numbers. The dynamics of this species was unaffected by chamois numbers. While causality cannot be inferred from the data, these results are consistent with the hypothesis of a negative effect of red deer on chamois dynamics, thus supporting the occurrence of interference or exploitation competition between sympatric mountain‐dwelling ungulates. Understanding the processes underlying temporal dynamics is pivotal for informed management of wildlife. Consequences of interspecific competition should be carefully evaluated where the populations of the weaker competitor are of conservation concern, especially in the light of the negative effects of anthropogenic environmental change on animal populations.

Modelling white-tailed deer impacts on forest regeneration to inform deer management options at landscape scales

Long-term continuity of forest cover in eastern North America may be threatened in part by white-tailed deer (Odocoileus virginianus), but effectively managing that threat requires greater understanding of the multi-scale nature of deer browsing pressure and other forces affecting forest regeneration. We isolated the effects of white-tailed deer on the regeneration of ten ecologically and commercially important tree species across the state of New York by fitting forest regeneration models with variables representing fine-scale plant competition, stand-scale seed dispersal, and region-wide patterns of climate, land-use, and deer abundance. Deer effects were not consistent across species or space. Increasing deer abundance was associated with declining seedling abundance for six species (Acer rubrum, Picea rubens, Pinus strobus, Tsuga canadensis, Prunus serotina, and Abies balsamea), and nonlinear changes (peaking at intermediate deer abundance) for four species (Acer saccharum, Betula alleghaniensis, Fagus grandifolia, Fraxinus americana). Models further indicated: (1) in many areas, meaningful increases in tree seedling abundance may not be achievable by reducing deer abundance alone; (2) in some areas, modest reductions in deer abundance may improve forest regeneration—these would be of high deer management priority; and (3) in some areas, the magnitude of deer population reductions required to achieve meaningful improvement in forest regeneration may be too large to be practical. Predicting forest regeneration across heterogeneous landscapes is complex, and isolating the effects of deer requires greater understanding of multiple potentially limiting and interacting factors (e.g., land-use, climate, forest characteristics). Our approach, based on readily available spatial data, may help prioritize areas, define management goals, and lay a foundation for adaptive management of deer to improve forest regeneration.

Risk Factors for Bites and Diseases Associated With Black-Legged Ticks: A Meta-Analysis.

The emergence and spread of Lyme disease and other infections associated with black-legged ticks is causing a public health crisis. No human vaccines are currently available, and both diagnosis and treatment are sometimes ineffectual, leading to advocacy for self-directed preventative measures. These recommendations are widely communicated to the public, but there is limited evidence for their efficacy. We undertook a systematic review and mixed-effects meta-regression analysis of factors purported to increase or decrease risk of black-legged tick bites and tick-borne disease. Published articles used in the study spanned the years 1984–2018. Variables associated with increased probability of tick-borne disease, with odds ratios significantly greater than 1, included deer abundance, high density of nymph-stage black-legged ticks, landscapes with interspersed herbaceous and forested habitat, low human population density, gardens, cat ownership, and race. Contrary to recommendations, use of landscape-related tick control measures, such as clearing brush, trimming branches, and having a dry barrier between lawn and woods, tended to increase risk. Pet ownership increased bite risk. Bite risk was highest for children aged 5 years or less, with a secondary peak in persons aged 50–70 years. Although some widely disseminated recommendations are supported by the research analyzed, others require further evaluation. Additional research is also needed to understand the mechanisms underlying significant relationships.

Integrating data from different survey types for population monitoring of an endangered species: the case of the Eld\u2019s deer

Despite its value for conservation decision-making, we lack information on population abundances for most species. Because establishing large-scale monitoring schemes is rarely feasible, statistical methods that combine multiple data sources are promising approaches to maximize use of available information. We built a Bayesian hierarchical model that combined different survey data of the endangered Eld’s deer in Shwesettaw Wildlife Sanctuary (SWS) in Myanmar and tested our approach in simulation experiments. We combined spatially-restricted line-transect abundance data with more spatially-extensive camera-trap occupancy data to enable estimation of the total deer abundance. The integrated model comprised an ecological model (common to both survey types, based on the equivalence between cloglog-transformed occurrence probability and log-transformed expected abundance) and separate observation models for each survey type. We estimated that the population size of Eld’s deer in SWS is c. 1519 (1061–2114), suggesting it is the world’s largest wild population. The simulations indicated that the potential benefits of combining data include increased precision and better sampling of the spatial variation in the environment, compared to separate analysis of each survey. Our analytical approach, which integrates the strengths of different survey methods, has widespread application for estimating species’ abundances, especially in information-poor regions of the world.

DISTRIBUTION AND STATUS OF MULE DEER (ODOCOILEUS HEMIONUS) IN OKLAHOMA: AN UPDATED ANALYSIS OF HARVEST DATA

Although the species is not actively managed in the state, the Oklahoma Department of Wildlife Conservation does collect and archive mule deer (Odocoileus hemionus) annual harvest data through mandatory hunter self-reporting of killed deer. We analyzed harvest records in an attempt to update the distribution and abundance of mule deer in the state and to infer population trends for years 2009–2016. In total, we recorded 1,585 mule deer over this time, and abundance of mule deer harvests consistently followed a northwest-to-southeast gradient, with the highest abundance occurring in the Oklahoma Panhandle. However, mule deer abundance in the state is low (<1 individual/km2). Results here suggest Oklahoma's mule deer population is stable, especially in the panhandle. In addition, we detected a significant, although weak, correlation with precipitation, with harvests decreasing with decreased precipitation.

Changing land use and increasing abundance of deer cause natural regeneration failure of oaks: Six decades of landscape-scale evidence

Many tree species worldwide are suffering from slow or failed natural regeneration with dramatic consequences for biodiversity and ecosystem services. However, it is difficult to disentangle the complex effects of factors influencing regeneration processes on long-lived tree species at large scales. In this study, we use long-term data from the Swedish National Forest Inventory (1953–2015) combined with deer hunting data (1960–2015) to reveal experimentally-intractable processes impeding oak (Quercus spp.) regeneration in southern Sweden. Oak-dominated ecosystems are widespread in northern temperate regions, where oaks are foundation species with disproportionate importance for biodiversity and ecosystem functions. Our study reveals that during the last six decades, oak tree numbers and standing volume have continuously increased, while natural regeneration of oak declined steeply after the early 1980s. We connect this decline to denser and darker forests, combined with increased abundance of deer. Land use changes during the six decades, such as abandonment of traditional practices and large-scale introduction of forest management oriented towards high volume production, led to continuously denser forests and thereby reduced the oak regeneration niche. In addition, the impact of changed game management was evident. This was particularly clear from a natural experiment on Gotland, a large island free of deer until roe deer were introduced in the late 20th century, at which point oak regeneration began a steep decline. At the stand level, natural oak regeneration could be expected to mainly occur in pulses after disturbance events, followed by a period of low regeneration success as the cohort ages. However, at a landscape scale one would expect a mix of successional stages that would even out such demographic patterns. A prolonged period of low regeneration at a landscape scale will eventually lead to a large gap in the oak size distribution as was observed in this study. This could eventually hurt the many species dependent on old and large oak trees. Active management to restore the oak regeneration niche, i.e. forest habitats with more light and less browsing pressure, therefore seems essential. The latter includes developing strategies that manage both deer populations and their available food across landscapes. Our study is the first to link oak regeneration failure to long-term changes in land use and increased deer populations at a landscape scale in this region. Furthermore, our study show how historical data can clarify confounded processes impacting long-lived forest species.

Validation of Body Condition Indicators for Monitoring Changes in Populations of Sika Deer (Cervus nippon) at a Landscape Scale

The estimated number of sika deer within the Tanzawa Mountains has decreased since the Kanagawa Prefecture sika deer management plan commenced. Meanwhile, unit-specific culling has resulted in various trends in deer density across small monitoring units. Deer abundance is usually surveyed within small monitoring units; therefore, the evaluation of deer abundance changes across the entire management area comprising individual units is difficult. We examined the relationship between deer body condition indicators and densities estimated at both individual unit and entire management scales in the Tanzawa Mountains during 2004–2015. Winter fawn body mass in the study area increased at least until 2011, irrespective of the increase/decrease in deer density in each unit. Observed variations in body mass were related to the estimated number of deer within the entire management area. Winter fawn hind foot length was not related to any density estimates. Inconsistencies between deer density changes in each unit and body mass might derive from the deer movement between units and mitigation of density-dependent food limitations caused by a reduction in the number of deer within the entire management area. We suggest that winter fawn body mass can provide additional evidence of deer abundance changes within management areas.

Pregled metod za določanje številčnosti prostoživečih parkljarjev

The information on absolute and/or relative abundance of wild ungulates is one of the key parameters for sustainable and efficient management. Wild ungulates are the most important and abundant group of game species in Slovenia; however, there are currently no standard census methods, which would be performed on the annual basis. There are various methods for estimating wild ungulate abundance and several criteria have to be met, when selecting the most suitable one. The most important criteria that have to be taken into account are studied species, habitat characteristics, size of the studied area, population density and cost efficiency. Besides the faecal pellet group method, which has already been used in Slovenia to estimate the abundance of roe deer and red deer, a suitable method is also the kilometre index. The reliable methods for wild boar are camera traps, drive counts and distance sampling with thermovision and, for chamois, ground counts and aerial counts.

Landscape structure affects the prevalence and distribution of a tick-borne zoonotic pathogen

BackgroundLandscape structure can affect pathogen prevalence and persistence with consequences for human and animal health. Few studies have examined how reservoir host species traits may interact with landscape structure to alter pathogen communities and dynamics. Using a landscape of islands and mainland sites we investigated how natural landscape fragmentation affects the prevalence and persistence of the zoonotic tick-borne pathogen complex Borrelia burgdorferi (sensu lato), which causes Lyme borreliosis. We hypothesized that the prevalence of B. burgdorferi (s.l.) would be lower on islands compared to the mainland and B. afzelii, a small mammal specialist genospecies, would be more affected by isolation than bird-associated B. garinii and B. valaisiana and the generalist B. burgdorferi (sensu stricto).MethodsQuesting (host-seeking) nymphal I. ricinus ticks (n = 6567) were collected from 12 island and 6 mainland sites in 2011, 2013 and 2015 and tested for B. burgdorferi (s.l.). Deer abundance was estimated using dung transects.ResultsThe prevalence of B. burgdorferi (s.l.) was significantly higher on the mainland (2.5%, 47/1891) compared to island sites (0.9%, 44/4673) (P < 0.01). While all four genospecies of B. burgdorferi (s.l.) were detected on the mainland, bird-associated species B. garinii and B. valaisiana and the generalist genospecies B. burgdorferi (s.s.) predominated on islands.ConclusionWe found that landscape structure influenced the prevalence of a zoonotic pathogen, with a lower prevalence detected among island sites compared to the mainland. This was mainly due to the significantly lower prevalence of small mammal-associated B. afzelii. Deer abundance was not related to pathogen prevalence, suggesting that the structure and dynamics of the reservoir host community underpins the observed prevalence patterns, with the higher mobility of bird hosts compared to small mammal hosts leading to a relative predominance of the bird-associated genospecies B. garinii and generalist genospecies B. burgdorferi (s.s.) on islands. In contrast, the lower prevalence of B. afzelii on islands may be due to small mammal populations there exhibiting lower densities, less immigration and stronger population fluctuations. This study suggests that landscape fragmentation can influence the prevalence of a zoonotic pathogen, dependent on the biology of the reservoir host.

Ecological factors influencing winter field sign abundance of Korean water deer Hydropotes inermis argyropus in a temperate forest in South Korea

The objective of this study was to clarify ecological factors influencing winter field sign abundance of Korean water deer Hydropotes inermis argyropus in a temperate forest on Mt. Maehwa, Hongcheon, South Korea. There were significant differences in four variables of cover and three variables of forage between the different topographic features, part from the midstory vegetation coverage. Most of the winter field signs of Korean water deer were observed on the ridge. The abundance of feces and total field signs of Korean water deer varied considerably between the topographical features. The understory vegetation, midstory vegetation, forb and shrub coverage, topography, understory vegetation × topography, midstory vegetation × topography, and shrub × topography were higher value of relative variable importance among habitat variables. Understory and midstory vegetation coverage, forage and topography were important ecological factors for affecting winter field sign abundance of Korean water deer.

High burdens of Ixodes scapularis larval ticks on white-tailed deer may limit Lyme disease risk in a low biodiversity setting

An inverse relationship between biodiversity and human health has been termed the ‘dilution effect’ paradigm. In the case of tick-borne infections such as Lyme disease, the key assumption is that Borrelia burgdorferi sensu lato abundance is increased by the loss of less competent (dilution) hosts as biodiversity declines. White-tailed deer play a dual role in the pathogen cycle, as key reproductive hosts for adult ticks and incompetent hosts for the pathogen. While the role of deer as hosts of adult ticks is well established, the extent to which deer also feed immature ticks and reduce the proportion infected is unknown because of logistic constraints in measuring this empirically. We estimated the proportion of larvae that fed on deer in an extremely species-poor community on Block Island, RI, where tick nymphal infection prevalence was found to be lower than expected. In 2014, we measured the density, larval tick burdens, and realized reservoir competence of small mammal and bird hosts on Block Island, RI. In 2015, we measured the infection prevalence of host-seeking Ixodes scapularis nymphs resulting from larvae fed on available hosts in 2014. We back-estimated the proportion of larvae expected to have fed on deer in 2014 (the only unknown parameter) to result in the nymphal infection prevalence observed in 2015. Back-estimation predicted that 29% of larval ticks must have fed on deer to yield the observed 30% nymphal infection prevalence. In comparison, the proportion of larvae feeding on mice was 44% and 27% on birds. Our study identified an influential role of deer in reducing nymphal tick infection prevalence and a potential role as dilution hosts if the reduction in nymphal infection prevalence outweighs the role of deer as tick population amplifiers. Because both deer and competent hosts may increase in anthropogenic, fragmented habitats, the links between fragmentation, biodiversity, and Lyme disease risk may be complex and difficult to predict. Furthermore, a nonlinear relationship between deer abundance and Lyme disease risk would reduce the efficacy of deer population reduction efforts to control Lyme disease.

Deer Browsing Influences Population Dynamics of the Ozark Baltimore Checkerspot (Euphydryas Phaeton Ozarkae: Nymphalidae)

White-tailed Deer (Odocoileus virginianus) have been shown to be detrimental to a number of Lepidoptera. Potential host plants for specialist butterfly species can be reduced and removed from native areas through deer browsing. The Ozark Baltimore Checkerspot (Euphydryas phaeton ozarkae) is a univoltine nymphalid butterfly endemic to the Ozark regions of Arkansas, Kansas, Missouri, and Oklahoma. In the area around the Buffalo River in Arkansas, the larval host for this butterfly is Smooth Yellow False Foxglove (Aureolaria flava). We examined the timing and quantified the effect that deer foraging had on A. flava in four E. p. ozarkae populations. Browsing occurred in late spring and reduced plant availability by as much as 87% over a two-month period. Browsed plants lost an average of 44 cm in height; data show taller plants were more likely to be browsed than shorter ones. Extensive herbivory caused early-fall-active and late-spring-active larvae to contend with reduced host plant availability, which likely resulted in increased mortality. We also found that browsed plants were less likely to be selected for oviposition. The amount of plant loss appeared to be associated with deer abundance and area attributes (i.e., slope, human activity, plant density, etc.). We found that browsing by White-tailed Deer that is too intense or prolonged can have important consequences for the Ozark Baltimore Checkerspot.