Browsing by Subject "MaxEnt"
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Item Open Access Estimating the population size of lemurs based on their mutualistic food trees(Journal of Biogeography, 2018-11-01) Herrera, JP; Borgerson, C; Tongasoa, L; Andriamahazoarivosoa, P; Rasolofoniaina, BJR; Rakotondrafarasata, ER; Randrianasolo, JLRR; Johnson, SE; Wright, PC; Golden, CDAim: Species’ distributions and abundances are primarily determined by the suitability of environmental conditions, including climate and interactions with sympatric species, but also increasingly by human activities. Modelling tools can help in assessing the extinction risk of affected species. By combining species distribution modelling of abiotic and biotic niches with population size modelling, we estimated the abundance of 19 lemur taxa in three regions, especially focusing on 10 species that are considered Endangered or Critically Endangered. Location: Madagascar. Taxa: Lemurs (Primates) and angiosperm trees. Methods: We used climate data, field samples, and published occurrence data on trees to construct species distribution models (SDM) for lemur food tree species. We then inferred the SDMs for lemurs based on the probability of occurrence of their food trees as well as climate. Finally, we used tree SDMs, topography, distance to the forest edge, and field estimates of lemur population density to predict lemur abundance in general linear models. Results: The SDMs of lemur food trees were stronger predictors of the occurrence of lemurs than climate. The predicted probability of presence of food trees, slope, elevation, and distance from the forest edge were significant correlates of lemur density. We found that sixteen species had minimum estimated abundances greater than 10,000 individuals over >1,000km2. Three lemur species are especially threatened, with less than 2,500 individuals predicted for Cheirogaleus sibreei, and heavy hunting pressure for the relatively small populations of Indri indri and Hapalemur occidentalis. Main conclusions: Biotic interactors were important variables in SDMs for lemurs, allowing refined estimates of ranges and abundances. This paper provides an analytical workflow that can be applied to other taxonomic groups to substantiate estimates of species’ vulnerability to extinction.Item Open Access Exploring Past and Future Distributions of the Rare Appalachian Oak Fern Using MaxEnt Modeling(American Fern Journal, 2023-06-16) Hay, NM; Akinwuntan, JV; Cai, V; Windham, MD; Pryer, KMAbstract . Anthropogenic climate change is projected to have an especially negative impact on the survival of plants that are dependent on limited microclimatic refugia or that already reside at their climatic extreme. Gymnocarpium appalachianum is a narrowly endemic fern restricted to cold mountaintops and algific vents in the central and southern Appalachian region of eastern North America. It is the much rarer of the two documented diploid parents of the circumboreal allotetraploid G. dryopteris - one of the most widespread fern species on the planet. Gymnocarpium appalachianum is a good case study for forecasting how evolutionarily significant, but rare, species might survive on a warming planet. We utilize an ecological niche modeling approach (MaxEnt) to explore the projected distribution of G. appalachianum under past (Last Glacial Maximum) and future climate models. All known verified herbarium records of G. appalachianum were georeferenced, for a total of 70 occurrence points. Nineteen standard bioclimatic variables extracted from WorldClim were used to model near-current climate projections; representative concentration pathways (RCPs 2.6 and 8.5) were used for future climate projections (2070). The temperature annual range, mean temperature of warmest quarter, precipitation of driest month, precipitation of coldest quarter, and mean diurnal range were identified as the key variables for shaping the distribution of G. appalachianum. An unanticipated result from our analyses is that G. appalachianum has past and current projected habitat suitability in Alaska. Because this overlaps with the current range of G. disjunctum, the other diploid parent of G. dryopteris, it suggests a possible region of origin for this circumboreal tetraploid descendent of G. appalachianum - a research avenue to be pursued in the future. Our study envisions a dire fate for G. appalachianum; its survival will likely require an urgent contingency plan that includes human-mediated population relocation to cooler, northern locations. Understanding the long-term sustainability of narrowly endemic plants such as G. appalachianum is critical in decisions about their management and conservation.Item Open Access Hunting for Hidden Wetlands: An Exploratory Geospatial Analysis to Identify Depressional Wetlands in the Sandhills Game Lands in North Carolina(2023-04-27) Paparone, Natalie AIn the Sandhills Game Lands of North Carolina, non-floodplain depressional wetlands are vital habitat for amphibian populations in conservation need. As such, it is imperative these landscape features be identified to ensure appropriate conservation and management. Non-floodplain depressional wetlands are ephemeral bowl-shaped wetlands that lack surface water connectivity to other bodies of water. These wetlands have been historically difficult to detect due to their small size and short periods of inundation. Recent research has shown that successful identification of these wetlands can be done using remote sensing and geospatial analysis. This project used a rule-based model and a maximum entropy (MaxEnt) model developed in ESRI ArcGIS Pro to create maps of potential non-floodplain depressional wetlands within the Sandhills Game Lands. Both models used topographic, vegetation, and wetness indices combined with known locations of existing wetlands to identify roughly 211 distinct non-floodplain depressional wetlands within the study area. Knowledge of these wetland locations can inform local land management, though predicted wetland locations should be validated in the field for accuracy.Item Open Access INVASIVE WEEDS IN GLACIER NATIONAL PARK: HABITAT, VECTORS OF SPREAD, AND AREAS AT GREATEST RISK OF INVASION(2009-04-24T18:03:26Z) Adams, AshleyNon-native invasive species have significantly changed the composition and ecosystem function of many North American landscapes. Currently, invasive species are recognized as the second greatest destroyer of biological diversity, superseded only by direct habitat destruction and consequent fragmentation from human development. Glacier National Park, an international Biosphere Reserve and World Heritage Site, is threatened by the encroachment of numerous noxious non-native invasive plant species. Prevention, early detection, and immediate action against invasive weed species in their initial establishment phases are paramount in reducing this threat. To facilitate strategic management actions, this study developed two maximum entropy invasive species distribution models for Glacier National Park. The first model was based entirely on environment variables associated with habitat, while the second model added environmental variables associated with vectors of spread to the environmental variables associated with habitat. The rationale behind the nested model approach was to determine invasion potential based on high quality invasive species habitat followed by invasion potential based on vectors of spread (keeping the relative influence of habitat constant). The two model results were then overlain to evaluate which areas were most susceptible to establishment of invasive species, the spatial distribution of these areas, and the locations with maximum potential for tactical management to prevent further invasive species spread. The analysis produced 10 nested species distribution model sets: a set for each of the 9 virulent priority invasive species individually and a set for all invasive species combined. For all invasive plant species combined, it was found that 30,928 acres (7.6%) of Glacier National Park had high quality invasive species habitat but lower invasion potential, 6,071 acres (1.5%) had high invasion potential but lower quality habitat, and 20,648 hectares (5.1%) had both high potential for invasion and high quality habitat. The latter was considered the area at greatest risk of invasion. The most influential vectors of spread were roads and trails, and the most important environmental factors were elevation, alluvial soils, slope, and forest land cover. Together, these findings and their spatial distributions allow Glacier National Park to prioritize invasive species monitoring, prevention and treatment.Item Open Access Searching for Eastern Old Growth: Modeling Primary Forest in Western North Carolina Using Terrain Attributes and Multispectral Satellite Imagery(2010-12-10) Hushaw, JenniferAfter centuries of timber harvest and conversion of forest to farmland and development, only small pockets of old growth forest remain in the eastern United States. These remnant portions of older forest have intrinsic value as a rare forest type and they play an important ecological function on the landscape. However, old growth forests in the eastern U.S. are less well-studied and documented than their counterparts in the Pacific Northwest. This study was undertaken to predict the geographic location, ecological and spectral characteristics of existing old growth, specifically in the southern Appalachian forests of western North Carolina. Stands of old growth previously field validated by the Southern Appalachian Forest Coalition were used as the response variable. Predictor variables included a range of landscape, topographic, and satellite indices derived from Landsat TM 7 satellite imagery and terrain analysis. Predictions were made using Classification and Regression Tree (CART) and Maximum Entropy (MaxEnt) modeling techniques. Model results were successful based on validation with existing field data. However, the MaxEnt model produced the most realistic estimate of potential old growth area given the inherent rarity of this forest type and suitability of the MaxEnt modeling technique for predicting the distribution of rare species. Results highlight over 54,000 hectares of potential old growth to be investigated by researchers on the ground. This analysis will contribute to the relatively limited body of knowledge about old growth in the eastern U.S. and is unique in terms of its broad geographic extent. Continued research on these remnant eastern old growth stands must be done to increase our understanding of this rare forest stage and to better inform related management decisions on both public and private land in the eastern U.S.