Adam Duarte

Global forest loss disproportionately erodes biodiversity in intact landscapes

Global biodiversity loss is a critical environmental crisis, yet the lack of spatial data on biodiversity threats has hindered conservation strategies. Theory predicts that abrupt biodiversity declines are most likely to occur when habitat availability is reduced to very low levels in the landscape (10–30%). Alternatively, recent evidence indicates that biodiversity is best conserved by minimizing human intrusion into intact and relatively unfragmented landscapes. Here we use recently available forest loss data to test deforestation effects on International Union for Conservation of Nature Red List categories of extinction risk for 19,432 vertebrate species worldwide. As expected, deforestation substantially increased the odds of a species being listed as threatened, undergoing recent upgrading to a higher threat category and exhibiting declining populations. More importantly, we show that these risks were disproportionately high in relatively intact landscapes; even minimal deforestation has had severe consequences for vertebrate biodiversity. We found little support for the alternative hypothesis that forest loss is most detrimental in already fragmented landscapes. Spatial analysis revealed high-risk hot spots in Borneo, the central Amazon and the Congo Basin. In these regions, our model predicts that 121–219 species will become threatened under current rates of forest loss over the next 30 years. Given that only 17.9% of these high-risk areas are formally protected and only 8.9% have strict protection, new large-scale conservation efforts to protect intact forests are necessary to slow deforestation rates and to avert a new wave of global extinctions.

Spatiotemporal variation in range‐wide Golden‐cheeked Warbler breeding habitat

Habitat availability ultimately limits the distribution and abundance of wildlife species. Consequently, it is paramount to identify where wildlife habitat is and understand how it changes over time in order to implement large-scale wildlife conservation plans. Yet, no work has quantified the degree of change in range-wide breeding habitat for the Golden-cheeked Warbler (Setophaga chrysoparia), despite the species being listed as endangered by the U.S. Federal Government. Thus, using available GIS data and Landsat imagery we quantified range-wide warbler breeding habitat change from 1999-2001 to 2010-2011. We detected a 29% reduction in total warbler breeding habitat and found that warbler breeding habitat was removed and became more fragmented at uneven rates across the warblers breeding range during this time period. This information will assist researchers and managers in prioritizing breeding habitat conservation efforts for the species and provides a foundation for more realistic carrying capacity scenarios when modeling Golden-cheeked Warbler populations over time. Additionally, this study highlights the need for future work centered on quantifying Golden-cheeked Warbler movement rates and distances in order to assess the degree of connectivity between increasingly fragmented habitat patches.

Estimating Abundance of the Endangered Houston Toad on a Primary Recovery Site

Abstract The Griffith League Ranch is one of the primary recovery sites for the endangered Houston toad Bufo (Anaxyrus) houstonensis. New recovery initiatives have recently been implemented to increase Houston toad abundance; however, no robust estimate of population size has been conducted in the last decade of study, nor from this recovery site. To assist with inferences regarding efficacy of current and future management actions, we estimated adult Houston toad abundance on the Griffith League Ranch. Houston toads were sampled at breeding ponds during the 2010 breeding season using a mark–recapture methodology. We analyzed the data using a modified Jolly–Seber open population model in Program MARK. Models were built whereby the probability of capture remained constant, the apparent survival varied with time or was constant, and the probability of entry varied with time. Model averaging was used to account for uncertainty and the derived adult male Houston toad abundance ranged from 201 to 307 individua...

Range expansion of nonindigenous caribou in the Aleutian archipelago of Alaska

Caribou (Rangifer tarandus) are nonindigenous to all but the eastern-most island of the Aleutian archipelago of Alaska. In 1958–1959, caribou were intentionally introduced to Adak Island in the central archipelago, and the population has at least tripled in recent years subsequent to the closure of a naval air facility. Although dispersal of caribou to adjacent islands has been suspected, no historical documentation has occurred to date. Herein, we report consistent detections of caribou sign on the adjacent island of Kagalaska over 2 summer field seasons (2010–2011), and visual detection of caribou on that island during the summer of 2011. Ecological impacts of caribou on Kagalaska are not strongly apparent at the present time and we do not know how many animals permanently occupy the island. However, establishment of a reproductively viable resident population on Kagalaska is worrisome and could set the stage for a step-wise invasion of additional nearby islands.

Does rumen–reticulum capacity correlate with body size or age in black-tailed deer?

To accommodate an increased food intake with greater body size, rumen–reticulum capacity must become larger to allow heavier digesta loads. Recently, digesta load was found to correlate with age more strongly than body size. It was suggested that older animals had compromised mastication efficiency due to tooth wear and compensated for larger particles by increasing rumen–reticulum capacity to extend retention time. Herein, we constructed models and used Akaike Information Criteria corrected for small sample size to determine if digesta load was related with age or body weight in 80 female and 105 male black-tailed deer (Odocoileus hemionus columbianus). We also assessed if the presence of fetuses influenced relationships in females. Females were collected in spring, 1985–1988, and males were collected in autumn, 1980, 1982–1984, and 1988, from Hopland Research and Extension Center, Mendocino County, California. Digesta loads, fetuses, and carcasses were weighed, and animal ages were estimated. Digesta load was related to age in females and body weight in males. Our study shows that body size and age-related factors may both influence rumen–reticulum capacity.

Vegetation changes associated with a population irruption by Roosevelt elk

Interactions between large herbivores and their food supply are central to the study of population dynamics. We assessed temporal and spatial patterns in meadow plant biomass over a 23-year period for meadow complexes that were spatially linked to three distinct populations of Roosevelt elk (Cervus elaphus roosevelti) in northwestern California. Our objectives were to determine whether the plant community exhibited a tolerant or resistant response when elk population growth became irruptive. Plant biomass for the three meadow complexes inhabited by the elk populations was measured using Normalized Difference Vegetation Index (NDVI), which was derived from Landsat 5 Thematic Mapper imagery. Elk populations exhibited different patterns of growth through the time series, whereby one population underwent a complete four-stage irruptive growth pattern while the other two did not. Temporal changes in NDVI for the meadow complex used by the irruptive population suggested a decline in forage biomass during the end of the dry season and a temporal decline in spatial variation of NDVI at the peak of plant biomass in May. Conversely, no such patterns were detected in the meadow complexes inhabited by the nonirruptive populations. Our findings suggest that the meadow complex used by the irruptive elk population may have undergone changes in plant community composition favoring plants that were resistant to elk grazing.

Climatic and density influences on recruitment in an irruptive population of Roosevelt elk

Abstract Current paradigms of ungulate population ecology recognize that density-dependent and independent mechanisms are not always mutually exclusive. Long-term data sets are necessary to assess the relative strength of each mechanism, especially when populations display irruptive dynamics. Using an 18-year time series of population abundances of Roosevelt elk (Cervus elaphus roosevelti) inhabiting Redwood National Park in northwestern California we assessed the influence of population size and climatic variation on elk recruitment and whether irruptive dynamics occurred. An information-theoretic model selection analysis indicated that abundance lagged 2 years and neither climatic factors nor a mix of abundance and climatic factors influenced elk recruitment. However, density-dependent recruitment differed between when the population was declining and when the population increased and then stabilized at an abundance lower than at the start of the decline. The population displayed irruptive dynamics.

Age-specific survival of male golden-cheeked warblers on the Fort Hood Military Reservation, Texas

Population models are essential components of large-scale conservation and management plans for the federally endangered Golden-cheeked Warbler (Setophaga chrysoparia; hereafter GCWA). However, existing models are based on vital rate estimates calculated using relatively small data sets that are now more than a decade old. We estimated more current, precise adult and juvenile apparent survival (Φ) probabilities and their associated variances for male GCWAs. In addition to providing estimates for use in population modeling, we tested hypotheses about spatial and temporal variation in Φ. We assessed whether a linear trend in Φ or a change in the overall mean Φ corresponded to an observed increase in GCWA abundance during 1992-2000 and if Φ varied among study plots. To accomplish these objectives, we analyzed long-term GCWA capture-resight data from 1992 through 2011, collected across seven study plots on the Fort Hood Military Reservation using a Cormack-Jolly-Seber model structure within program MARK. We also estimated Φ process and sampling variances using a variance-components approach. Our results did not provide evidence of site-specific variation in adult Φ on the installation. Because of a lack of data, we could not assess whether juvenile Φ varied spatially. We did not detect a strong temporal association between GCWA abundance and Φ. Mean estimates of Φ for adult and juvenile male GCWAs for all years analyzed were 0.47 with a process variance of 0.0120 and a sampling variance of 0.0113 and 0.28 with a process variance of 0.0076 and a sampling variance of 0.0149, respectively. Although juvenile Φ did not differ greatly from previous estimates, our adult Φ estimate suggests previous GCWA population models were overly optimistic with respect to adult survival. These updated Φ probabilities and their associated variances will be incorporated into new population models to assist with GCWA conservation decision making. Survie en fonction de l’âge des Parulines a dos noir mâles sur la reserve militaire de Fort Hood, Texas RESUME. Les modeles de population sont des elements essentiels des plans de gestion et de conservation a grande echelle pour la Paruline a dos noir (Setophaga chrysoparia; abregee PADN ci-dessous), designee « menacee » par le gouvernement federal etatsunien. Toutefois, les modeles existants sont fondes sur des estimations de taux vitaux calculees a partir d’echantillons relativement petits qui datent maintenant de plus d’une decennie. Nous avons actualise et precise la probabilite de survie apparente (Φ) adulte et juvenile et calcule les variances associees pour les mâles PADN. En plus de ces estimations destinees a la modelisation des populations, nous avons teste les hypotheses de variations spatiale et temporelle de Φ. Nous avons evalue si une tendance lineaire de Φ ou un changement de Φ moyen correspondait a une augmentation reelle du nombre de PADN de 1992 a 2000, et si Φ avait varie entre les parcelles echantillonnees. Pour atteindre nos objectifs, nous avons analyse les donnees de capture-reobservation de PADN de 1992 a 2011, recoltees dans sept parcelles situees sur la reserve militaire de Fort Hood, Texas, au moyen d’une structure de modele de Cormack-Jolly-Seber avec le programme MARK. Nous avons aussi estime les composantes de la variance de Φ associees au processus et a l’echantillonnage en les partitionnant. Nos resultats n’ont pas confirme qu’il existait une variation du Φ adulte propre au site. A cause du petit echantillon de donnees, nous n’avons pas pu determiner si le Φ juvenile avait varie spatialement. Nous n’avons pas detecte d’association temporelle forte entre le nombre de PADN et Φ. L’estimation moyenne de Φ s’elevait a 0,47 pour les mâles adultes, avec une variance relative au processus de 0,0120 et une variance relative a l’echantillonnage de 0,0113, et atteignait 0,28 pour les mâles juveniles, avec une variance relative au processus de 0,0076 et une variance relative a l’echantillonnage de 0,0149. Alors que notre estimation de Φ juvenile ne differe pas grandement des estimations anterieures, notre estimation de Φ adulte indique que les modeles precedents de population pour la PADN etaient trop optimistes quant a la survie des adultes. Ces probabilites actualisees de Φ et leurs variances seront incluses dans de nouveaux modeles de population afin de contribuer a la prise de decision touchant la conservation de la PADN.

Intraspecific Scaling of Rumen-reticulum Fill Might Depend on Dietary Fiber

Abstract Body mass – gut fill scaling relationships affect rate of digestion, foraging behavior, niche differentiation, and trophic interactions. On an intraspecific level, the scalar of this relationship has been reported to be both iso- and allometric (<1.0). We hypothesized the scalar of rumen-reticulum fill depends on diet. When the diet has low concentrations of indigestible fiber the scalar should be allometric to fulfill metabolic demands and isometric when the diet has high concentrations of indigestible fiber as both small and large animals have difficulties processing forage. We collected 50 male and 50 female white-tailed deer (Odocoileus virginianus) over a 30 h period from a site in south Texas in Oct. Animals ranged in body mass from 32 to 106 kg. We also recorded collection time, sex, lactation status of females, back fat thickness, and tooth wear. These covariates affected the body mass – rumen-reticulum fill relationship. Acid detergent fiber, our surrogate of indigestible fiber, in the rumen contents of our study animals was lower in concentration than in another study of white-tailed deer that estimated an isometric scalar for rumen-reticulum fill. The estimated scalar between body mass and rumen-reticulum fill in our study was 0.74 and allometric. Rumen-reticulum fill probably was influenced by chemostatic feedback and mechanisms were governed by metabolic demands. Rumen-reticulum fill scalars for white-tailed deer are not static but dynamic.

Response of lizards to high-severity wildfires in a southern United States mixed pine/hardwood forest

High-severity forest fires are increasing in large areas of the southern and western United States as the climate becomes warmer and drier. Natural resource managers need a better understanding of the short- and long-term effects of wildfires on lizard populations, but there is a paucity of studies focused on lizard-wildfire relationships. We used a before-after, control-impact (BACI) sample design to assess the response of three lizard species—Six-lined Racerunner (Aspidoscelis sexlineata), Prairie Lizard (Sceloporus consobrinus), and Little Brown Skink (Scincella lateralis)—to high-severity wildfires that occurred in the Lost Pines Ecoregion, Texas, USA. Specifically, we analyzed monitoring data collected across 17 trapping sessions from spring 2008 to spring 2013 using stratified N-mixture models to estimate trends in lizard abundances, while accounting for environmental parameters that might influence lizard detectability. We found no evidence of a fire-induced change in abundance for any of the lizard species we studied, but there was an increase in detectability of A. sexlineata following the wildfires. Detectability of A. sexlineata and S. lateralis increased with air temperature, detectability of S. consobrinus decreased with precipitation, and detectability was related to Julian day for all three species. Mean detection probabilities were low (<0.1), suggesting capture-mark-recapture methods at a subset of sample units should be implemented to derive more accurate estimates in future monitoring efforts. Our results provide quantitative evidence of the short-term effects of high-severity wildfires on three widely distributed lizard species. Given the wildfires did not result in decreased lizard abundances, managers should minimize their vehicle footprints off of roads during post-wildfire habitat restoration to avoid soil compaction and the potential for direct mortality.