Exotic Predators Research Articles

Relative strength of top-down effects of an invasive fish and bottom-up effects of nutrient addition in a simple aquatic food web.

Introduction of exotic predators or runoff of fertilizers can alter aquatic food webs, in particular zooplankton communities, through top-down and bottom-up effects. In a mesocosm experiment, we manipulated the density of Western Mosquitofish (Gambusia affinis) and nutrient levels (nitrate and phosphate independently) and observed effects on zooplankton and phytoplankton in a fall, temperate zone system. If top-down regulation were important, we expected mosquitofish predation to reduce zooplankton abundance, which would indirectly benefit phytoplankton. If bottom-up regulation were important, we expected nutrient addition to increase both primary producers and zooplankton. Western Mosquitofish predation significantly decreased the abundance of several zooplankton taxa, resulting in a trophic cascade with increased chlorophyll a (i.e., primary productivity). This effect did not differ between mesocosms with 5 or 10 fish. Nutrient addition had no significant effects on zooplankton; however, chlorophyll a was positively affected by both nitrogen addition and phosphorus addition. Our results suggest weak bottom-up regulation in our experimental community, but strong top-down regulation, emphasizing the potential consequences of introducing non-native Western Mosquitofish to native aquatic ecosystems.

Scrutinizing the enemy release hypothesis: population effects of parasitoids on Harmonia axyridis and local host coccinellids in Brazil

The Enemy Release Hypothesis (ERH) has been a factor influencing the establishment of some exotic species worldwide. We tested if the ERH could be influencing populations of the exotic predator Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in Brazil. During two years, three local predatory coccinellid species and Harmonia axyridis were sampled in Brassica oleracea in six organic farms in the midwest of the country. Parasitoids were detected by rearing (emerged) and qPCR Melting Curve Analysis (unemerged). Host density-dependence and spillovers were used to evaluate coccinellid population effects of parasitism. Six parasitoid species were found, including two new records for Brazil. Although Harmonia axyridis harbored fewer parasitoid species, parasitism was not lower and parasitoid density-dependence was not weaker on it compared to the local species. Spillovers among hosts occurred both onto Harmonia axyridis and from it. The ERH was rejected for these parasitoids and, therefore, it did not contribute to the invasiveness of Harmonia axyridis in Brazil.

Knowledge status of predators of the freshwater prawn Cryphiops caementarius (Decapoda: Palaemonidae) in river systems along the North Western Andean region from Perú and Chile

Introduction: Cryphiops caementarius, is an endemic prawn from river ecosystems in Southern Perú and Northern Chile. In these watersheds, natural populations are threatened by multiple anthropic interventions such as mining activities and fishing pressure, but also, by increasing impacts of invasive exotic predators. Information related with predation on C. caementarius is scarce representing a major knowledge gap to ensure suitable management and conservation practices. Accordingly, the further deepening in relevant aspects such as the estimation of populations losses due to predators has been indicated as critical by relevant agencies as FAO. Objective: To conduct a complete registry and classification of C. caementarius predators, updating the knowledge for the Andean region. Methods: A thorough bibliographic review on existing information on C. caementarius' predators from Perú and Chile was carried out calculating percentage of occurrence, relative frequency of species, zoogeographic origin, trophic structure, phenotypic attributes, river zone that inhabits and life stage of incidence. The registry was complemented using semi-structured interviews from prawn´s fishers in central-Northern Chile. Results: C. caementarius is predated along the entire fluvial network (estuary, potamon and rhithron) by 21 species of opportunists, carnivores, omnivores and herbivores, mostly aquatic vertebrates. In turn, these belong to 15 families and six guilds of native, exotic and cosmopolitan species. Approximately 86 % predate on adult prawns, whilst, 71 % on juveniles and 24 % on larvae. More than 40 % of the predation pressure seems to be exerted by native waterfowls and 24 % by exotic fish. Conclusions: The results emphasize the relevance for conservation of native species of predators in the Andean region and the need of control measures on exotic species in a latitudinal basis. Accordingly, this review may serve as an initial decision-making tool for future conservation efforts both on prawns and native biota, but also supporting restocking actions, fisheries management plans and risk assessment for C. caementariuspopulations across the Andean region.

Female reproductive suppression in an Australian arid zone rodent, the spinifex hopping mouse

AbstractThe spinifex hopping mouse (Notomys alexis) is an Australian arid zone rodent that undergoes boom and bust population cycles in its natural environment. Most populations studied to date have been sympatric with exotic predators and introduced herbivores, likely affecting their population dynamics. Therefore, it is unclear whether high‐density populations of hopping mice are regulated by purely extrinsic factors or whether intrinsic factors are also at play. We hypothesized that reproductive suppression of female N. alexis may occur in high‐density populations as has been observed in some other rodent species. Reproductive condition of adult female N. alexis was compared between a high‐density population within the Arid Recovery reserve, where exotic predators and introduced herbivores are excluded, and a low‐density population on adjacent pastoral properties (no exclusions). Trap success was 10 times higher inside the reserve than at pastoral sites, and no adult females were observed breeding in the reserve population, despite 26 % of females at pastoral sites recorded breeding. Our results indicate that adult female N. alexis in the high‐density reserve population were reproductively suppressed, but the similar sex ratios in both populations and the high female body mass and body condition in the reserve indicated that this was not due to demographic differences between the two populations or food scarcity. Our study indicates that the ‘busts’ observed in arid zone rodent populations may be amplified due to the presence of exotic predators and/or grazing by introduced herbivores. We contend that prior to the introduction of exotic predators and introduced herbivores in Australia, the arid zone rodent N. alexis would likely have been more abundant and intrinsic population regulation through female reproductive suppression may have played a larger role in population regulation.

PERLUNY A EVALUASI KINERJA PARASITOID PADA HAMA DAUN KELAPA : BRONTISPA LONGISSIMA GESTRO (COLEOPTERA: CHRYSOMELIDAE) DI KABUPATEN ENDE-FLORES

Brontispa longissima Gestro (Coleoptera: Chrysomelidae) is ones of the most important pest who attack of many family palms in South East Asia. In Indonesia, Brontispa longissima has. becomes a primer pest on coconut. It was Decreasing yield result up to 30 - 40 % returns and 5% of the attacked crops will die. Ones of the failed reason of control action is a low preventive system on every territory entrance, otherwise, coconut was a needful and fast-moving commodity for people and industry. The second reason is secondary commodity assumes and low cropping system caused pest and disease uncontrolled. Three bio-control usages on-field need to monitored caused farmers incapable. The success indicator for parasitoid release was quick and easy to adapt for the parasitoid. It was related " three-generation three years," theory by Ev Clausen, the expert of integrated pest and management control from California says: a) The perfectly of Effective parasitoid/predator always quick and easy to adapt, b) The failed parasitoid/predator to adapt easily and quickly was an ineffective indicator for bio-control, c) Parasitoid release or exotic predator could be stopped for 3 years if no evidence adapt on fields. According to the experts, the key for the success of system controlling above depends on cropping agroecosystem stability.

Experimental high-density trapping of social wasps: target kairomones for workers or gynes for drones?

ABSTRACT Social wasps are amongst the most loathed exotic predators in New Zealand, with widespread adverse impacts on native ecosystems and fauna. Sustainable alternatives to pesticides are sorely needed in Fuscospora (beech) forests. We tested a new semiochemical evaluation protocol to assess the extent of high-density trap competition as an indicator of mass trapping, in an open landscape adjacent to a beech forest near Cass (Canterbury, New Zealand), for potential worker or drone removal. We tested the kairomone lure using a before-after control-impact design at a 1-ha scale with a grid of 25 bucket traps as a high-density trapping treatment (three replicates). The trial was affected by a major inundation event and catches declined steadily in both treatments for the month following, and treatment effects were not significantly different. Drone captures in sticky traps showed a dose response in catch to 1, 3 or 10 gynes (virgin queens). Sticky traps baited with three gynes in a 5 × 5 array over 1 ha (four replicates), caught a mean of 7.39 (±0.88) drones per trap per day across the high density and control traps (n = 116), but there was no difference in the number of drones caught per central trap in the control and treatment plots (n = 4 per plot), demonstrating the limitations of our methods under extreme population pressure in such a mobile species. It is proposed that the gyne sex pheromone be identified and investigated for potential use in area-wide suppression, as it holds more promise as an attractant than the kairomones tested.http://www.zoobank.org/urn:lsid:zoobank.org:act:C0809A1F-87C2-431C-BA14-548F00D954F9

Global determinants of prey naiveté to exotic predators.

Prey naiveté-the failure of prey to recognize novel predators as threats-is thought to exacerbate the impact that exotic predators exert on prey populations. Prey naiveté varies under the influence of eco-evolutionary mediating factors, such as biogeographic isolation and prey adaptation, although an overall quantification of their influence is lacking. We conducted a global meta-analysis to test the effects of several hypothesized mediating factors on the expression of prey naiveté. Prey were overall naive towards exotic predators in marine and freshwater systems but not in terrestrial systems. Prey naiveté was most pronounced towards exotic predators that did not have native congeneric relatives in the recipient community. Time since introduction was relevant, as prey naiveté declined with the number of generations since introduction; on average, around 200 generations may be required to erode naiveté sufficiently for prey to display antipredator behaviour towards exotic predators. Given that exotic predators are a major cause of extinction, the global predictors and trends of prey naiveté presented here can inform efforts to meet conservation targets.

Multiple-threats analysis for loggerhead sea turtles in the southwest Atlantic Ocean

Priority-setting approaches for widely distributed and long-lived species can be challenging. This is especially true for sea turtles, which are species of conservation concern. The aim of this study was to conduct a detailed analysis of threats to identify, quantify and prioritize the main impacts to the loggerhead Caretta caretta population in the southwest Atlantic (SWA) region. A matrix of relative threats was constructed. Threats were identified and classified for 8 different life stages (nesting females, eggs, hatchlings, swim-frenzy transitional stage, juveniles-neritic, juveniles-oceanic, adults-neritic, adults-oceanic) and for 3 ecosystems inhabited by sea turtles (terrestrial, neritic and oceanic). Results indicated that fisheries bycatch represents a major threat for loggerheads in the SWA. The trawl fishery was identified as the main source of mortality for neritic juvenile and adult turtles, whereas juveniles in oceanic areas are mostly impacted by surface longlines. In terrestrial environments, eggs and hatchlings are mainly affected by habitat alteration and by native and exotic predators. Loggerheads have shown a positive nesting trend at their main nesting beaches in the SWA, probably due to long-term conservation efforts to reduce mortality of the different life stages within the terrestrial zone. However, the high mortality rates of juveniles and sub-adults documented at some known foraging grounds represent a reason for concern, as this may affect the overall population trend in the future. This threat analysis provides a tool to review the goals of national action plans, prioritize actions and optimize the allocation of management resources.

A comparative study of survival, recruitment and population growth in two translocated populations of the threatened greater bilby (Macrotis lagotis)

Abstract Context Translocations have been widely used to re-establish populations of threatened Australian mammalian species. However, they are limited by the availability of sites where key threats can be effectively minimised or eliminated. Outside of ‘safe havens’, threats such as exotic predators, introduced herbivores and habitat degradation are often unable to be completely eliminated. Understanding how different threats affect Australian mammal populations can assist in prioritising threat-management actions outside of safe havens. AimsWe sought to determine whether translocations of the greater bilby to two sites in the temperate zone of South Australia could be successful when human-induced threats, such as prior habitat clearance, historic grazing, the presence of feral cats and European rabbits, could not be completely eliminated. Methods Greater bilbies were regularly cage trapped at two translocation sites and a capture–mark–recapture study was used to determine survival, recruitment and population growth at both sites. Key results Our study showed that bilbies were successfully translocated to an offshore island with a previous history of grazing and habitat clearance, but which was free of exotic predators. At a second site, a mainland exclosure with feral cats and European rabbits present, the bilby population declined over time. Adult bilbies had similar survival rates in both populations; however, the mainland bilby population had low recruitment rates and low numbers of subadults despite high adult female fecundity. ConclusionsThe results indicated that past grazing and habitat clearance did not prevent the bilby population on the offshore island establishing and reaching a high population density. In the mainland exclosure, the low recruitment is probably due to feral cats predating on subadult bilbies following pouch emergence. Implications The results demonstrated that the bilby, an ecologically flexible Australian marsupial, can be successfully translocated to sites with a history of habitat degradation if exotic predators are absent. At the mainland exclosure site, threat mitigation for bilbies should focus on control or eradication of the feral cats. The control of European rabbits without control of feral cats could lead to prey-switching by feral cats, further increasing predation pressure on the small bilby population.

Population decline of the noisy scrub-bird is not correlated with territory size, marginal declines in rainfall or fire impacts

The noisy scrub-bird is endangered and confined to one natural population on Mount Gardner and several translocated populations east of Albany, Western Australia. Annual monitoring of the number of singing males at Mount Gardner since 1966 indicates a steady rise in numbers, peaking at 179 birds in 1994 followed by a less regular decline to 19 by 2017. The Lakes, an adjacent location, had a similar pattern of increase from the early 1970s then irregular decline from the mid-1980s. Broken stick regression models confirmed that both apparent patterns represented significant increase then decline in the number of singing males. Territory size estimates from 1994, 2005 and 2014 suggest an increase in size of territories over time but that pattern was not significant when only common territories were compared. Variance in bird numbers was not correlated with annual rainfall, which has broadly declined over the study period, or with number of rain days. We discuss five possible causes of decline: (1) inbreeding, (2) control of exotic predators and associated impact on non-target, natural predators, (3) resource/food availability (which may interact with rainfall), (4) removal of birds for introduction programs, and (5) the absence of wildfire and associated changes (senescence) in vegetation. None are compelling, single explanations for decline but their collective impact may be high. Survival of the noisy scrub-bird may be increasingly dependent on the introduced, managed populations of this species at Mount Manypeaks and on Bald Island.

Occupancy Modeling Reveals Interspecific Variation in Habitat Use and Negative Effects of Dogs on Lemur Populations

Effective, targeted management and conservation plans for wildlife populations require reliable population sampling and estimation. Unfortunately, robust, comprehensive primate population estimates are often lacking, particularly for rare, elusive species. Historically, population estimates of primates have relied on labor-intensive line-transect sampling and distance estimation techniques. We used occupancy sampling to estimate the probability of occupancy and detection of seven lemur species in Ranomafana National Park, Madagascar, and explore relationships between occupancy and detection and landscape, habitat, and co-occurring species variables. We detected and provide estimates of occupancy and/or detection for seven lemur species in a World Heritage Site: Ranomafana National Park, Madagascar. We found habitat type was an important variable explaining occupancy patterns for detection of golden bamboo lemur (Hapalemur aureus), as well as red bellied lemur (Eulemur rubriventer) and black-and-white ruffed lemur (Varecia variegata). The presence of free-ranging dogs (Canis familiaris) was an important factor in several competing models for red-bellied lemurs and eastern lesser bamboo lemurs (Hapalemur griseus), highlighting the threat posed by this exotic predator to primates. While some estimates had error values overlapping zero, reflecting the rarity and low detection of these species, these results indicate the importance of protecting multiple forest types to maintain lemur biodiversity and the underappreciated conservation threat of invasive species in Madagascar.

Habitat selection and genetic diversity of a reintroduced ‘refugee species’

AbstractA ‘refugee’ species is one with a current distribution that has been restricted to a subset of their former niche by threatening processes. Conservation opportunities for such species can be limited by a poor understanding of habitat requirements, where habitat models are based on current distributions and not the innate capacity of the animal to survive where threats are managed. We examined patterns of habitat selection by a putative refugee species, the threatened New Holland mouse Pseudomys novaehollandiae, following reintroduction into historic habitat (habitat that corresponds to a currently unoccupied component of its former niche). Current New Holland mouse populations exist predominantly in coastal heath habitat of select vegetation and fire history, and these environmental conditions differ greatly to those found across the species historical distribution. Using a novel, non‐invasive method of detection for the species, we investigated patterns of habitat selection following reintroduction into historic habitat, where the species primary threat of exotic predators has been removed. We also assessed the changes in genetic diversity measures across three stages of the reintroduction process (before, during and after) using microsatellite markers, to reflect on past efforts in maintaining genetic diversity. We found that historic habitat can still support New Holland mouse populations and identified more diverse potential habitat for the species. We also identified loss of alleles and an increased inbreeding coefficient at the captive breeding stage, but these findings were not statistically significant. This study expands on our limited understanding of habitat requirements and the fundamental niche of the New Holland mouse, highlighting new potential conservation opportunities.

Deciphering Geographical Affinity and Reconstructing Invasion Scenarios of Boa imperator on the Caribbean Island of Cozumel

Invasive species represent a major threat for biodiversity. The numbers of independent introductions, introduced propagules, and introduction episodes are critical aspects for invasion success. Here, we traced the source(s) of introduction and determined the historical route of invasion in order to understand the main stages of the invasion process. However, we often must rely on indirect information when studying invasive species (i.e., not knowing where the invasive population originated), hence requiring robust analytical methods to solve those questions. The invasive population of the snake Boa constrictor in the Mexican Caribbean (Cozumel Island) has been studied ecologically and genetically, but, despite several lines of evidence suggesting its invasive nature, a full account of its invasive history is lacking. Here, we aimed to reconstruct the boa's invasion history by deciphering the original source(s) of the Cozumel population, routes of invasion, likely number of propagules, and estimation of historical genetic and demographic parameters, based on a comprehensive set of analytical tools including tree topology-based methods and Approximate Bayesian Computational algorithms. The phylogenetic relationship of the Cozumel boa within the Boa constrictor complex was unknown; hence, to identify the source populations, we first needed to clarify its genealogical relationships. We used mitochondrial and nuclear sequences and nuclear microsatellites, together with the widest geographic sampling along the species' entire continental distribution. With our genetic approach, we demonstrate that the Cozumel population was derived from an admixture of individuals from different geographic localities. Moreover, our demography results allowed us to successfully confirm both anecdotal and previous genetic information, concordant with a scenario in which a likely small number of propagules were released on the island about 50 years ago. Notably, national law hinders the possibility of performing any control protocols for the boa, hence our results highlight a rather unique conservation paradox, where the Cozumel boa has a novel endangered protected species status as B. imperator, but it is also an invasive exotic predator threatening the critically endangered endemic and native biota of Cozumel. Therefore, any conservation decisions should consider that boas in Cozumel are invasive, opening the possibility to legally allow implementing control or eradication programs.

A structured analysis of risk to important wildlife elements in three Australian Wildlife Conservancy sanctuaries

SummaryWhere data and information are lacking, structured expert risk assessments can provide a powerful tool to progress natural resource planning. In many situations, practitioners make informal assessments of risk within small groups that typically constitute employees. In this study, we report on three small (in terms of experts) structured expert‐based risk assessment case studies conducted by expert employees of a not‐for‐profit organisation (Australian Wildlife Conservancy) to demonstrate the utility of the approach. The case studies were carried out for three wildlife sanctuaries managed by AWC: Faure Island, Karakamia and Paruna. The likelihood that a set of direct risk factors would cause management failure for sets of important wildlife elements in the three sanctuaries was elicited from the small group of ecological experts. The analysis was couched in terms of a management aim to not lose species from each wildlife element over the management period of 25 years with current management. The experts believed, in particular, that increasing temperature and decreasing water availability associated with climate change were likely to impact significantly upon the vegetation elements and water‐reliant fauna associated with the sanctuaries. Some vegetation elements were also thought likely to be at risk of over‐grazing, unsuitable fire regimes and, in some cases, disease. In addition to predation by exotic predators at one sanctuary, the experts identified additional direct risk factors for various fauna elements associated with expected changes to the vegetation elements, including reduction in food availability, nesting habitat, and generally important life media. From the risk analyses, a preliminary conceptual model was developed to underpin monitoring and to indicate areas for possible management intervention and research. The case studies demonstrate that even in a small workplace team, structured risk assessments can be efficiently accomplished and can provide expedient and transparent information that effectively captures and aggregates the views of the experts.

Digging mammal reintroductions reduce termite biomass and alter assemblage composition along an aridity gradient.

Invasions can trigger cascades in ecological communities by altering species interactions. Following the introduction of cats and foxes into Australia, one tenth of Australia's terrestrial mammal species became extinct, due to predation, while many continue to decline. The broader consequences for Australian ecosystems are poorly understood. Soil-dwelling invertebrates are likely to be affected by the loss of fossorial native mammals, which are predators and disturbance agents. Using reintroductions as a model for ecosystems prior to species loss, we tested the hypothesis that mammal reintroduction leads to reduced vegetation cover and altered termite assemblages, including declines in abundance and biomass and changed species composition. We hypothesised that the magnitude of mammal reintroduction effects would diminish with increasing aridity, which affects resource availability. We compared six paired sites inside and outside three reintroduction sanctuaries across an aridity gradient. We sampled termite assemblages using soil trenches and measured habitat availability. Reintroductions were associated with increased bare ground and reduced vegetation, compared with controls. Aridity also had an underlying influence on vegetation cover by limiting water availability. Termite abundance and biomass were lower where mammals were reintroduced and the magnitude of this effect decreased with increasing aridity. Termite abundance was highest under wood, and soil-nesting wood-feeders were most affected inside sanctuaries. Ecological cascades resulting from exotic predator invasions are thus likely to have increased termite biomass and altered termite assemblages, but impacts may be lower in less-productive habitats. Our findings have implications for reserve carrying capacities and understanding of assemblage reconstruction following ecological cascades.

Predictors of translocation success of captive‐reared lizards: implications for their captive management

AbstractIslands are biodiversity hotspots, but their native inhabitants are vulnerable to predation from exotic predators. Conservation of island endemics has often involved translocating captive‐reared populations to predator‐free refugia. However, the long‐term success of these translocations has rarely been assessed. We investigated the traits that maximize post‐translocation survival in a cohort of captive‐reared Suter's skinks Oligosoma suteri and compared traits normally associated with survival and persistence of lizards (body condition, speed and overall size) to that of wild‐born skinks 6 years after release onto a predator‐free island in the north‐east of New Zealand. Our models showed that larger lizards, and lizards with lower body condition, had improved survival. While sprint speed of captive‐reared lizards did not differ significantly to that of wild skinks, diving ability of captive‐reared skinks was poor, with only female captive‐reared lizards diving during trials. Our results indicate that the traits associated with higher survival after release are not necessarily obvious and may be influenced by adaptation to captive conditions. Long‐term monitoring post‐translocation is therefore vital to determine the success of the translocation.

Habitat use at fire edges: Does animal activity follow temporal patterns of habitat change?

Edges are ecologically important environmental features that have been well researched in agricultural and urban landscapes. However, little work has been conducted in flammable ecosystems where spatially and temporally dynamic fire edges are expected to influence animal activity patterns, particularly for animals reliant on vegetation for cover, foraging or nesting. We quantified the response of ground-dwelling mammals to fire edges and sought to determine whether animal activity mirrored temporal changes in regenerating understorey vegetation. We used a space-for-time substitution sampling design and selected a series of 26 treatment sites burnt by prescribed fire, where time since fire ranged from 0 to 7 years. Ten long-unburnt sites acted as controls. At each treatment site we identified a burnt/unburnt edge and used camera traps and Elliott traps to survey ground-dwelling mammals on either side. Habitat structure was measured at all 36 sites. We used general and generalised linear mixed models to determine the response of both habitat and animals to time since fire on both burnt and unburnt sides of edges. In addition, we used a resource selection index to assess the congruence between changes in understorey complexity and animal activity identified in the first set of analyses. On the unburnt side of the edge understorey complexity remained constant over time. On the burnt side understorey complexity followed a hump-shaped trend, peaking at 3 years post-fire where it exceeded the level of complexity on the unburnt edge. Larger animals with general resource requirements were more active at burnt compared to unburnt edges immediately after fire, but similarly active on both sides of fire edges from three years post-fire. Despite some activity on the burnt side of edges immediately after fire, small mammals were generally less active on burnt edges compared to unburnt edges for up to three years. Native species’ activity did not follow patterns of temporal change in structurally complex understorey vegetation. For all species, selection was strongest at recently burnt edges with little vegetation and substantially lower at 3–7 year old regenerating edges where understorey complexity was higher. In general, patterns of selection on the unburnt side of edges were similar over time. Our findings suggest that vegetation change on the burnt side of fire edges may not be a good predictor of native mammal use. Foxes and cats, exotic predators in our system, were also using the burnt edge more than expected immediately after fire. Immediate post-fire predation may be higher at fire edges than elsewhere, and recently burnt edge zones could be suitable locations for integrated predator and fire management.

Towards recovery of an endangered island endemic: Distributional and behavioral responses of Key Largo woodrats associated with exotic predator removal

Exotic predators create novel ecological contexts for native species, particularly when prey exhibit predator naïve behaviors. Population recovery of island endemic species following predator eradication has been documented broadly, but studies examining mammalian prey behavioral responses to exotic predator removal are less common. The Key Largo woodrat (Neotoma floridana smalli) is an endangered Florida endemic species that exhibited drastic declines, signified by the loss of natural stick-nests, over the past three decades due to habitat loss and effects from exotic predators. We conducted camera trap surveys of woodrats at supplemental nests and used dynamic multistate occupancy models to evaluate changes in woodrat distribution and stick-nest building behavior over a two-year period of exotic predator (domestic cats [Felis catus] and Burmese pythons [Python bivittatus]) removal. The distribution of woodrats using supplemental nests increased from 27% to 39% in the two-year period, while the proportion of occupied supplemental nests with stick-nests increased from 37% in 2013 to 54% in 2015. The probabilities of supplemental nest use and stick-nest building behavior increased over time following a gradient away from the northern extent of Key Largo, an area associated with high cat activity and the only sites of python captures during the surveys. Woodrats that built stick-nests were more detectable than those that did not, which suggests that stick-nest building could make woodrats more susceptible to predation from novel predators when performing the behavior. We documented increasing woodrat occurrence, along with increasing stick-nest building behavior, which supports recovery and management objectives focused on exotic predator removal.

HABITAT USE, MOVEMENT PATTERNS, AND NEST SITE SELECTION BY WESTERN POND TURTLES (ACTINEMYS MARMORATA) IN A MANAGED CENTRAL CALIFORNIA RANGELAND POND

The Western Pond Turtle (Actinemys marmorata) has been declining throughout its range due to several stressors, including habitat degradation and loss, exotic competitors, nonnative predators, and epidemic disease. California's only native turtle is listed as a Species of Special Concern and a candidate species for listing under the federal Endangered Species Act. Few studies have examined their population ecology in lentic environments subject to livestock grazing. From 2011 through 2016, staff and volunteers from the East Bay Regional Park District used radiotelemetry or tracked visually the seasonal movement patterns, habitat use, and nest site selection of Western Pond Turtles (n = 38) in eastern Contra Costa County, California. Statistical analyses of this multiple-year database showed that male and female turtles used the pond environment differently; however, they all overwintered in the same relative location. Gravid females on average moved 24.4 m (s = 17.5 m.) away from the ponds during the first 2 wk of June to oviposit on south-facing slopes (aspect = 134°, s = 31.9°), with mean residual-dry-matter levels of 1345 lbs/ac (1510 kg/ha) and vegetation heights ranging between 26.6 and 39.5 cm. These findings on how Western Pond Turtles used their pond and upland environments may have significant conservation and management implications for rangelands.

Prey Responses to Exotic Predators: Effects of Old Risks and New Cues.

Exotic predators can have major negative impacts on prey. Importantly, prey vary considerably in their behavioral responses to exotic predators. Factors proposed to explain variation in prey response to exotic predators include the similarity of new predators to familiar, native predators, the prevalence and diversity of predators in a prey's past, and variation in a prey's innate ability to discriminate between predators and safety. While these factors have been put forth verbally in the literature, no theory exists that combines these hypotheses in a common conceptual framework using a unified behavioral model. Here, we formalize existing verbal arguments by modeling variation in prey responses to new predators in a state-dependent detection theory framework. We find that while some conventional wisdom is upheld, novel predictions emerge. As expected, prey respond poorly to exotic predators that do not closely resemble familiar predators. Furthermore, a history with more abundant or diverse native predators can lessen effects of some exotic predators on prey; however, under some conditions, the opposite prediction emerges. Also, prey that evolved in situations where they easily discriminate between safe and dangerous situations can be more susceptible to novel predators.