Individual-based modeling highlights the importance of mortality and landscape structure in measures of functional connectivity

Landscape Ecology - Functional landscape connectivity is vital for the conservation of wildlife species. Landscape connectivity models often overlook factors such as mortality and asymmetry in...     

Sustainable management of wildlife habitat and risk of extinction

Whether land management planning provides for sufficient habitat to sustain viable populations of indigenous wildlife is one of the greatest challenges confronting resource managers. Analyses of the effects of land management on natural resources often rely on qualitative assessments that focus on single species to reflect the risk of wildlife extinction across a planning area. We propose a conceptual framework for sustainable management of wildlife habitat that explicitly acknowledges the greater risk of an extinction event when considering the viability of multiple species, e.g., an indigenous vertebrate fauna. This concept is based on the principle that the likelihood of at least one event (i.e., species extinction) is the joint probability of the extinction probabilities of individual species, assuming independence among species’ responses to disturbance. We present an ecological rationale to support the view that, at a spatial scale of 10⁴-10⁶ ha (i.e., planning area) and a temporal scale of 10² years (i.e., planning horizon), wildlife species operating at varying ecological scales respond relatively independently to disturbances typically associated with land management. We use a hypothetical scenario of a wildlife viability assessment and Monte Carlo simulation to demonstrate that the probability of ‘any extinction’ is consistently higher than the probability of the ‘single most likely’ extinction, and that the difference between these values increases as more disturbance-sensitive species (i.e., species at risk) are analyzed. We conclude that risk assessments that rely upon the most sensitive single species may substantially underestimate the risk of wildlife extinction across a planning area. Furthermore, the selection of a planning alternative based on relative threat of local extinction of wildlife populations can vary depending on which paradigm is used to estimate risk to viability across the planning area.     

Human influence on the abundance and connectivity of high-risk fuels in mixed forests of northern Wisconsin,USA

Though fire is considered a natural disturbance, humans heavily influence modern wildfire regimes. Humans influence fires both directly, by igniting and suppressing fires, and indirectly, by either altering vegetation, climate, or both. We used the LANDIS disturbance and succession model to compare the relative importance of a direct human influence (suppression of low intensity surface fires) with an indirect human influence (timber harvest) on the long-term abundance and connectivity of high-risk fuel in a 2791 km² landscape characterized by a mixture of northern hardwood and boreal tree species in northern Wisconsin. High risk fuels were defined as a combination of sites recently disturbed by wind and sites containing conifer species/cohorts that might serve as ladder fuel to carry a surface fire into the canopy. Two levels of surface fire suppression (high/current and low) and three harvest alternatives (no harvest, hardwood emphasis, and pine emphasis) were compared in a 2×3 factorial design using 5 replicated simulations per treatment combination over a 250-year period. Multivariate analysis of variance indicated that the landscape pattern of high-risk fuel (proportion of landscape, mean patch size, nearest neighbor distance, and juxtaposition with non fuel sites) was significantly influenced by both surface fire suppression and by forest harvest (p > 0.0001). However, the two human influences also interacted with each other (p < 0.001), because fire suppression was less likely to influence fuel connectivity when harvest disturbance was simultaneously applied. Temporal patterns observed for each of seven conifer species indicated that disturbances by either fire or harvest encouraged the establishment of moderately shade-tolerant conifer species by disturbing the dominant shade tolerant competitor, sugar maple. Our results conflict with commonly reported relationships between fire suppression and fire risk observed within the interior west of the United States, and illustrate the importance of understanding key interactions between natural disturbance, human disturbance, and successional responses to these disturbance types that will eventually dictate future fire risk.This revised version was published online in May 2005 with corrections to the Cover Date.     

Influence of forest planning alternatives on landscape pattern and ecosystem processes in northern Wisconsin,USA

Incorporating an ecosystem management perspective into forest planning requires consideration of the impacts of timber management on a suite of landscape characteristics at broad spatial and long temporal scales. We used the LANDIS forest landscape simulation model to predict forest composition and landscape pattern under seven alternative forest management plans drafted for the Chequamegon-Nicolet National Forest in Wisconsin. We analyzed 20 response variables representing changes in landscape characteristics that relate to eight timber and wildlife management objectives. A MANOVA showed significant variation in the response variables among the alternative management plans. For most (16 out of 20) response variables, plans ranked either directly or inversely to the extent of even-aged management. The amount of hemlock on the landscape had a surprising positive relationship with even-aged management because hemlock is never cut, even in a clear cut. Our results also show that multiple management objectives can create conflicts related to the amount and arrangement of management activities. For example, American marten and ruffed grouse habitat are maintained by mutually exclusive activities. Our approach demonstrates a way to evaluate alternative management plans and assess if they are likely to meet their stated, multiple objectives.     

Influence of forest management alternatives and land type on susceptibility to fire in northern Wisconsin,USA

We used the LANDIS disturbance and succession model to study the effects of six alternative vegetation management scenarios on forest succession and the subsequent risk of canopy fire on a 2791 km² landscape in northern Wisconsin, USA. The study area is a mix of fire-prone and fire-resistant land types. The alternatives vary the spatial distribution of vegetation management activities to meet objectives primarily related to forest composition and recreation. The model simulates the spatial dynamics of differential reproduction, dispersal, and succession patterns using the vital attributes of species as they are influenced by the abiotic environment and disturbance. We simulated 50 replicates of each management alternative and recorded the presence of species age cohorts capable of sustaining canopy fire and the occurrence of fire over 250 years. We combined these maps of fuel and fire to map the probability of canopy fires across replicates for each alternative. Canopy fire probability varied considerably by land type. There was also a subtle, but significant effect of management alternative, and there was a significant interaction between land type and management alternative. The species associated with high-risk fuels (conifers) tend to be favored by management alternatives with more disturbances, whereas low disturbance levels favor low-risk northern hardwood systems dominated by sugar maple. The effect of management alternative on fire risk to individual human communities was not consistent across the landscape. Our results highlight the value of the LANDIS model for identifying specific locations where interacting factors of land type and management strategy increase fire risk.This revised version was published online in May 2005 with corrections to the Cover Date.     

Comparing the landscape level perceptual abilities of forest sciurids in fragmented agricultural landscapes*

Perceptual range is the maximum distance from which an animal can perceive the presence of remote landscape elements such as patches of habitat. Such perceptual abilities are of interest because they influence the probability that an animal will successfully disperse to a new patch in a landscape. Furthermore, understanding how perceptual range differs between species may help to explain differential species sensitivity to patch isolation. The objective of this research was to assess the perceptual range of eastern chipmunks (Tamias striatus), gray squirrels (Sciurus carolinensis), and fox squirrels (Sciurus niger) in fragmented agricultural landscapes. Animals were captured in remote woodlots and translocated to unfamiliar agricultural fields. There they were released at different distances from a woodlot and their movements towards or away from the woodlot were used to assess their ability to perceive forested habitat. Observed perceptual ranges of approximately 120 m for chipmunks, 300 m for gray squirrels, and 400 m for fox squirrels, suggest that differences in landscape-level perceptual abilities may influence the occurrence of these species in isolated habitat patches.     

Modeling the indirect effects of road networks on the foraging activities of bats

Negative impacts of road networks on wildlife are of global concern. While direct mortality of wildlife via roads has been well-documented, we know little about indirect effects of roads. Using a simulation model parameterized from empirical data, we explored how roads in proximity to maternity roosts influenced foraging activities of the endangered Indiana bat. First, we conducted manipulated landscape simulations to identify characteristics (such as traffic volume, foraging habitat availability, etc.) that influenced landscape permeability. We used a classification and regression tree procedure to assess which landscape and road-related variables, alone or in combination, influenced bat movement. We determined that roads did act as filters (>10 vehicles/5 min) or barriers (>200 vehicles/5 min) to movement. However, it is a combination of the proportion of foraging habitat accessible without crossing a road, and roost-to-road distance that dictated whether the barrier and filter effects of roads hindered the bats’ foraging abilities. We then simulated movement patterns and foraging success of Indiana bats at 32 existing maternity roosts to identify conditions under which colonies currently persist. We established a foraging success threshold, above which Indiana bats currently persist. The value represents the time virtual bats spend in foraging habitat during the simulation period. Finally, simulations from these landscapes around known maternity roosts demonstrate that the road network and landscape configuration are critical to foraging success. This modeling approach and threshold value are beneficial to road developers and represent an invaluable tool in the ecological design of transportation infrastructures.     

Ivory-billed woodpecker (Campephilus principalis) persists in continental North America

The ivory-billed woodpecker (Campephilus principalis), long suspected to be extinct, has been rediscovered in the Big Woods region of eastern Arkansas. Visual encounters during 2004 and 2005, and analysis of a video clip from April 2004, confirm the existence of at least one male. Acoustic signatures consistent with Campephilus display drums also have been heard from the region. Extensive efforts to find birds away from the primary encounter site remain unsuccessful, but potential habitat for a thinly distributed source population is vast (over 220,000 hectares).     

Modeling relative habitat suitability of southern Florida for invasive Burmese pythons (<Emphasis Type="Italic">Python molurus bivittatus</Emphasis>)

Context

Invasive Burmese pythons are altering the ecology of southern Florida and their distribution is expanding northward. Understanding their habitat use is an important step in understanding the pathways of the invasion.

Objectives

This study identifies key landscape variables in predicting relative habitat suitability for pythons at the present stage of invasion through presence-only ecological niche modeling using geographical sampling bias correction.

Methods

We used 2014 presence-only observations from the EDDMapS database and three landscape variables to model habitat suitability: fine-scale land cover, home range-level land cover, and distance to open freshwater or wetland. Ten geographical sampling bias correction scenarios based on road presence and sampling effort were evaluated to improve the efficacy of modeling.

Results

The best performing models treated road presence as a binary factor rather than a continuous decrease in sampling effort with distance from roads. Home range-level cover contributed the most to the final prediction, followed by proximity to water and fine-scale land cover. Estuarine habitat and freshwater wetlands were the most important variables to contribute to python habitat suitability at both the home range-level and fine-scale. Suitability was highest within 30 m of open freshwater and wetlands.

Conclusions

This study provides quantifiable, predictive relationships between habitat types and python presence at the current stage of invasion. This knowledge can elucidate future targeted studies of python habitat use and behavior and help inform management efforts. Furthermore, it illustrates how estimates of relative habitat suitability derived from MaxEnt can be improved by both multi-scale perspectives on habitat and consideration of a variety of bias correction scenarios for selecting background points.