Simultaneous modeling of habitat suitability, occupancy, and relative abundance: African elephants in Zimbabwe.
ABSTRACT The recent development of statistical models such as dynamic site occupancy models provides the opportunity to address fairly complex management and conservation problems with relatively simple models. However, surprisingly few empirical studies have simultaneously modeled habitat suitability and occupancy status of organisms over large landscapes for management purposes. Joint modeling of these components is particularly important in the context of management of wild populations, as it provides a more coherent framework to investigate the population dynamics of organisms in space and time for the application of management decision tools. We applied such an approach to the study of water hole use by African elephants in Hwange National Park, Zimbabwe. Here we show how such methodology may be implemented and derive estimates of annual transition probabilities among three dry-season states for water holes: (1) unsuitable state (dry water holes with no elephants); (2) suitable state (water hole with water) with low abundance of elephants; and (3) suitable state with high abundance of elephants. We found that annual rainfall and the number of neighboring water holes influenced the transition probabilities among these three states. Because of an increase in elephant densities in the park during the study period, we also found that transition probabilities from low abundance to high abundance states increased over time. The application of the joint habitat-occupancy models provides a coherent framework to examine how habitat suitability and factors that affect habitat suitability influence the distribution and abundance of organisms. We discuss how these simple models can further be used to apply structured decision-making tools in order to derive decisions that are optimal relative to specified management objectives. The modeling framework presented in this paper should be applicable to a wide range of existing data sets and should help to address important ecological, conservation, and management problems that deal with occupancy, relative abundance, and habitat suitability.
- SourceAvailable from: Julee J. Boan[Show abstract] [Hide abstract]
ABSTRACT: Growing development pressures and expectations that forest managers provide future wildlife habitat require better understanding of species’ habitat needs, particularly food, cover, and space requirements, and an ability to spatially depict these needs. In forest management in Canada, the primary data used to identify and quantify wildlife habitat reside in remotely sensed forest resource inventories (FRI) that were originally developed to assess timber values for merchantable tree species. Although FRI- and field-based sampling do not always show strong agreement, research has shown that FRI can be informative for wildlife habitat assessments. However, much uncertainty remains when investigating forest characteristics that are not visible to the interpreters, such as sub-canopy features. Here, we used 152 plots in northwestern Ontario to compare the ability of field-based and remotely sensed forest inventories to predict Cladonia lichen cover, a primary winter food source for woodland caribou. The best model for field-based data, which included percentage of jack pine and black spruce in the tree canopy, tree height, stand age, soil moisture, and stem density, correctly predicted 92% of cases where Cladonia spp. were absent (n = 107 plots) and 62% of cases where they were present (i.e., cover >1%; n = 45 plots). FRI performed poorly by contrast, with corresponding percentages of 96 and 19%. FRI provide weak data support for differentiating winter forage availability for woodland caribou, an important habitat factor at the stand level. These findings have important implications for predictions of herd productivity, and suggest that improved remote-sensing capabilities are required in order to assess woodland caribou winter habitat. L'augmentation des pressions d’exploitation et des attentes auprès des gestionnaires forestiers pour qu’ils assurent l’avenir des habitats fauniques exige une compréhension des besoins des espèces liés à l’habitat, en particulier pour l'alimentation, l’abri et l’espace nécessaire, ainsi que la capacité de les représenter spatialement. Au Canada, les principales données utilisées en aménagement forestier pour reconnaître et évaluer quantitativement les habitats fauniques proviennent des inventaires des ressources forestières (IRF) réalisés par télédétection et développés à l'origine pour évaluer la valeur marchande des espèces commerciales d’arbres. Bien que les IRF et les données d’échantillonnage sur le terrain ne concordent pas toujours parfaitement, des recherches ont montré que les IRF peuvent fournir des informations utiles pour évaluer les habitats fauniques. Cependant, plusieurs incertitudes demeurent quant aux caractéristiques forestières qui ne sont pas visibles par les personnes qui analysent les images comme les caractéristiques du sous-étage. Dans cette étude, nous avons utilisé 152 parcelles forestières du nord-ouest de l'Ontario pour comparer les capacités des inventaires forestiers terrain et par télédétection à prédire la couverture de lichens Cladonia, une source principale de nourriture hivernale pour le caribou forestier. Le meilleur modèle pour les données de terrain incluait le pourcentage de pin gris et d'épinette noire dans le couvert forestier, la hauteur des arbres, l'âge du peuplement, l'humidité du sol et la densité de tiges. Ce modèle a prédit correctement 92 % des cas où les espèces de Cladonia étaient absentes (n = 107 parcelles) et 62 % des cas où ces lichens étaient presents (c'est-à-dire, couverture >1 %; n = 45 parcelles). À l’opposé, le modèle basé sur les IRF n’a pas bien performé avec des pourcentages correspondants de 96 % et 19 %. Les données des IRF étaient peu utiles pour différencier la disponibilité en fourrage hivernal pour le caribou forestier, un élément important de l’habitat au niveau du peuplement. Ces résultats ont des implications importantes pour prédire la productivité des troupeaux et suggèrent que des compétences de télédétection améliorées sont nécessaires pour évaluer l'habitat d'hiver du caribou forestier.Ecoscience 06/2013; 20(2):101-111. · 1.01 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Global conservation policy is increasingly debating the feasibility of reconciling wildlife conservation and human resource requirements in land uses outside protected areas (PAs). However, there are few quantitative assessments of whether or to what extent these ‘wildlife-friendly’ land uses fulfill a fundamental function of PAs—to separate biodiversity from anthropogenic threats. We distinguish the role of wildlife-friendly land uses as being (a) subsidiary, whereby they augment PAs with secondary habitat, or (b) substitutive, wherein they provide comparable habitat to PAs. We tested our hypotheses by investigating the influence of land use and human presence on space-use intensity of the endangered Asian elephant (Elephas maximus) in a fragmented landscape comprising PAs and wildlife-friendly land uses. We applied multistate occupancy models to spatial data on elephant occurrence to estimate and model the overall probability of elephants using a site, and the conditional probability of high-intensity use given that elephants use a site. The probability of elephants using a site regardless of intensity did not vary between PAs and wildlife-friendly land uses. However, high-intensity use declined with distance to PAs, and this effect was accentuated by an increase in village density. Therefore, while wildlife-friendly land uses did play a subsidiary conservation role, their potential to substitute for PAs was offset by a strong human presence. Our findings demonstrate the need to evaluate the role of wildlife-friendly land uses in landscape-scale conservation; for species that have conflicting resource requirements with people, PAs are likely to provide crucial refuge from growing anthropogenic threats.Biological Conservation 09/2014; 177:74–81. · 4.04 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Primates are a global conservation priority, with half of known species considered threatened with extinction. Monitoring trends in primate populations is important for identifying species in particular need of conservation action, and evaluating the effectiveness of interventions. Most existing primate survey methods aim to measure abundance. However, obtaining estimates of abundance with acceptable precision to detect changes in population is often expensive and time consuming. Evidence from other taxa suggests that estimating occupancy (the proportion of the area used by the species) may be less resource-intensive, yet still provide useful information for monitoring population trends. We investigate the potential of occupancy modelling for monitoring forest primates using a case study of three species of diurnal lemurs in the eastern rainforest of Madagascar. We estimated detectability and occupancy from a survey with three visits to 30 sites. Our estimates suggest that precision in occupancy estimates would be maximized by visiting a larger number of sites (therefore with limited repeat visits) for Indri indri, whereas the optimal monitoring design for Eulemur fulvus and Propithecus diadema, which showed very low detectability in our surveys, involves more frequent visits to fewer sites. Power analyses suggested that a meaningful reduction in occupancy could be detected with reasonable effort for easily detected species, but the method may prove impractical for more cryptic species. Primates pose a number of practical challenges for occupancy modelling, including choosing appropriate survey designs to satisfy closure assumptions. We suggest that if these issues can be overcome, occupancy modelling has the potential to become a valuable addition to the monitoring toolbox for the study of forest primates.Animal Conservation 10/2012; 15(5). · 2.69 Impact Factor