Spatial configuration becomes more important with increasing habitat loss: a simulation study of environmentally-transmitted parasites

Context

Landscape changes can be an important modifier of disease. Habitat fragmentation commonly results in reduced connectivity in host populations and increased use of the remaining habitat. For environmentally transmitted parasites, this presents a possible trade-off between transmission potential at the local and global level.

Objectives

We quantify the effects of fragmentation on the transmission of an environmentally transmitted parasite, teasing apart the relative effects of habitat composition and configuration on both host movement behaviour and subsequent infection patterns.

Methods

We use a spatially-explicit epidemiological model to simulate the effects of habitat fragmentation, using, as an example, whipworm (Trichuris sp.) within a red colobus monkey population (Procolobus rufomitratus).

Results

We found that habitat fragmentation did not always lead to a trade-off between population connectivity and concentration of habitat use in host movement behaviour or in final population infection patterns. However, our simulation results suggest the spatial configuration of the remaining habitat became increasingly influential on behavioural and infection outcomes as habitat was removed. Additionally, we found common fragmentation metrics provided little ability to explain variation in propagation of infections.

Conclusions

Our results suggest an interaction between habitat configuration and composition should be considered when assessing disease related impacts of habitat fragmentation on environmentally transmitted parasites, especially in cases where habitat loss is high (≥?30%). We also propose that spatially-explicit simulations that capture a host’s response to fragmentation could aid in the development of novel landscape metrics targeted towards specific host-parasite-landscape systems.

     

Multi-scale feedbacks between tree regeneration traits and herbivore behavior explain the structure of pasture-woodland mosaics

Context

The pasture-woodlands of Central Europe are low-intensity grazing systems in which the structural richness of dynamic forest-grassland mosaics is causal for their high biodiversity. Distinct mosaic patterns in Picea abies- and Fagus sylvatica-dominated pasture-woodlands in the Swiss Jura Mountains suggest a strong influence of tree species regeneration ecology on landscape structural properties. At the landscape scale, however, cause-effect relationships are complicated by habitat selectivity of livestock.

Objectives

We asked which tree species regeneration traits and what kind of feedbacks among local-scale vegetation dynamics and landscape-scale herbivore behavior are causal for the contrasted landscape structural characteristics of Picea- and Fagus-dominated pasture-woodlands.

Methods

We performed simulation experiments of mosaic pattern formation in both pasture-woodland types. The regeneration traits, namely dispersal distance, resistance to browsing and tolerance to shade, and the rules for habitat selection of cattle were modified and the corresponding shifts in landscape structure were analyzed.

Results

Dispersal distance showed a significant, but only local, effect promoting forest fringe formation. Saplings’ resistance to browsing mainly determined overall tree cover, but did not influence landscape structure. At the landscape scale, both shade tolerance of saplings and selective habitat use by cattle were responsible for forest-grassland segregation: high shade tolerance triggered segregation, whereas non-selective habitat use hindered it.

Conclusions

Existing local-scale theory on pasture-woodland dynamics is complemented by an herbivore-vegetation feedback among spatial scales. In low-intensity pastures, where large herbivores are preferentially “grazers” and trees form dense canopies, an intrinsic trend towards forest-grassland segregation at the expense of forest-grassland ecotones is predicted.

     

Are landscapes more than the sum of their patches?

Context

The species–area relationship (SAR) is the most ubiquitous scaling relationship in ecology, yet we still do not know how different aspects of scale affect this relationship. Scale is defined by grain, extent, and focus. Focus here pertains to whether patches or landscapes are used to derive SARs.

Objective

To explore whether altering the focal scale influences the resulting SAR. If the SAR is scale-invariant, patch-based and landscape-based SARs should be congruent.

Methods

I fit a power-law function (S = cA ^z) to arthropod data obtained from an experimental landscape system, in which habitat amount and configuration (clumped vs. fragmented) of red clover (Trifolium pratense) varied among plots (256 m²). The scaling coefficient (z) was compared among patch-based and landscape-based SARs for congruence.

Results

Patches gained species at a faster rate than landscapes (z = 0.37 vs. 0.26, respectively), producing domains of incongruity in the SAR. Landscape richness (S _L) was greater than patch richness (S _P) below 30 % habitat, but S _P > S _L above 60 % habitat. Landscape configuration contributed to this incongruity below 30 % habitat (fragmented S _L > clumped S _L), but landscape context (whether the largest patch was embedded in a fragmented or clumped landscape) was important above 60 % habitat for understanding the SAR in this domain.

Conclusions

Landscape configuration exerts both direct (<30 % habitat) and indirect (>60 % habitat) effects on the SAR. Because patch-based and landscape-based SARs may not be congruent, we should exercise care when extrapolating from patches to landscapes to make inferences about the effects of habitat loss and fragmentation on species richness.

     

Shaken but not stirred: multiscale habitat suitability modeling of sympatric marten species (<Emphasis Type="Italic">Martes martes</Emphasis> and <Emphasis Type="Italic">Martes foina</Emphasis>) in the northern Iberian Peninsula

Context

Multispecies and multiscale habitat suitability models (HSM) are important to identify the environmental variables and scales influencing habitat selection and facilitate the comparison of closely related species with different ecological requirements.

Objectives

This study explores the multiscale relationships of habitat suitability for the pine (Martes martes) and stone marten (M. foina) in northern Spain to evaluate differences in habitat selection and scaling, and to determine if there is habitat niche displacement when both species coexist.

Methods

We combined bivariate scaling and maximum entropy modeling to compare the multiscale habitat selection of the two martens. To optimize the HSM, the performance of three sampling bias correction methods at four spatial scales was explored. HSMs were compared to explore niche differentiation between species through a niche identity test.

Results

The comparison among HSMs resulted in the detection of a significant niche divergence between species. The pine marten was positively associated with cooler mountainous areas, low levels of human disturbance, high proportion of natural forests and well-connected forestry plantations, and medium-extent agroforestry mosaics. The stone marten was positively related to the density of urban areas, the proportion and extensiveness of croplands, the existence of some scrub cover and semi-continuous grasslands.

Conclusions

This study outlines the influence of the spatial scale and the importance of the sampling bias corrections in HSM, and to our knowledge, it is the first comparing multiscale habitat selection and niche divergence of two related marten species. This study provides a useful methodological framework for multispecies and multiscale comparatives.

     

Effect of connectivity and habitat availability on the occurrence of the Chestnut-throated Huet-Huet (<Emphasis Type="Italic">Pteroptochos castaneus,</Emphasis> Rhinocryptidae) in fragmented landscapes of central Chile

Context

Although small isolated habitat patches may not be able to maintain a minimum viable population, small patches that are structurally isolated may be functionally connected if individuals can cross the gaps between them, in which case, their areas could be added to form a larger habitat patch, eventually surpassing the size threshold for holding a viable population.

Objectives

We studied whether models based on the size and isolation of habitat patches could be used to predict the distribution of the Chestnut-throated Huet-Huet (Pteroptochos castaneus) in fragmented landscapes of the coastal range of the Maule region, central Chile.

Methods

We selected seven 10,000-ha landscapes (8.4–70.7% forest cover). For each habitat patch we made 18 predictions of the presence of the species based on the combination of two thresholds: three critical patch sizes for maintaining a viable population (62.5, 125 and 250 ha) and six critical isolation distances between patches (0, 10, 50, 100, 150 and 200 m). We used playbacks in 59 sampling points to estimate the species’ presence/absence. We used logistic regressions to test whether the output of the patch-matrix models could explain part of the variation in the presence of Pteroptochos castaneus.

Results

The best predictions for the presence of P. castaneus were obtained with the most conservative scenarios (125–250 ha to 0–10 m), including a positive effect of the understory cover and a lack of effect of the forest type (native or exotic).

Conclusions

Our findings suggest that the long term persistence of P. castaneus may depend on the existence of large and/or very connected forest tracts.

     

Occupancy pattern of a long-horned beetle in a variegated forest landscape: linkages between tree quality and forest cover across spatial scales

Context

Interactions between landscape-scale processes and fine-grained habitat heterogeneity are usually invoked to explain species occupancy in fragmented landscapes. In variegated landscapes, however, organisms face continuous variation in micro-habitat features, which makes necessary to consider ecologically meaningful estimates of habitat quality at different spatial scales.

Objectives

We evaluated the spatial scales at which forest cover and tree quality make the greatest contribution to the occupancy of the long-horned beetle Microplophorus magellanicus (Coleoptera: Cerambycidae) in a variegated forest landscape.

Methods

We used averaged data of tree quality (as derived from remote sensing estimates of the decay stage of single trees) and spatially independent pheromone-baited traps to model the occurrence probability as a function of multiple cross-scale combinations between forest cover and tree quality (with scales ranging between 50 and 400 m).

Results

Model support and performance increased monotonically with the increasing scale at which tree quality was measured. Forest cover was not significant, and did not exhibit scale-specific effects on the occurrence probability of M. magellanicus. The interactive effect between tree quality and forest cover was stronger than the independent (additive) effects of tree quality and particularly forest cover. Significant interactions included tree quality measured at spatial scales ≥200 m, but cross-scale interactions occurred only in four of the seven best-supported models.

Conclusions

M. magellanicus respond to the high-quality trees available in the landscape rather than to the amount of forest per se. Conservation of viable metapopulations of M. magellanicus should consider the quality of trees at spatial scales >200 m.

     

Spatiotemporal dynamics of the agricultural landscape mosaic drives distribution and abundance of dominant carabid beetles

Context

Agroecosystems are dynamic, with yearly changing proportions of crops. Explicit consideration of this temporal heterogeneity is required to decipher population and community patterns but remains poorly studied.

Objectives

We evaluated the impact on the activity-density of two dominant carabid species (Poecilus cupreus and Anchomenus dorsalis) of (1) local crop, current year landscape composition, and their interaction, and (2) inter-annual changes in landscape composition due to crop rotations.

Methods

Carabids were sampled using pitfall-traps in 188 fields of winter cereals and oilseed rape in three agricultural areas of western France contrasting in their spatial heterogeneity. We summarized landscape composition in the current and previous years in a multi-scale perspective, using buffers of increasing size around sampling locations.

Results

Both species were more abundant in oilseed rape, and in landscapes with a higher proportion of oilseed rape in the previous year. P. cupreus abundance was negatively influenced by oilseed rape proportion in the current year landscape in winter cereals and positively by winter cereal proportion in oilseed rape. A. dorsalis was globally impacted at finer scales than P. cupreus.

Conclusions

Resource concentration and dilution-concentration processes jointly appear to cause transient dynamics of population abundance and distribution among habitat patches. Inter-patch movements across years appear to be key drivers of carabids’ survival and distribution, in response to crop rotation. Therefore, the explicit consideration of the spatiotemporal dynamics of landscape composition can allow future studies to better evidence ecological processes behind observed species patterns and help developing new management strategies.

     

Drones for butterfly conservation: larval habitat assessment with an unmanned aerial vehicle

Context

Evidence-based nature conservation focuses on ecological facts and the incorporation of knowledge on the ecology of species, including its entire life cycle. In butterflies, imagos and its larvae often demand specific and diverging micro-habitat structures and resources. In consequence, ecological requirements of the imaginal and pre-imaginal stage have to be taken into consideration to conduct effective conservation management.

Objective

Here we analyse ecological pre-requisites of imagos and larvae for two lycaenid butterfly species, the common blue Polyommatus icarus and the adonis blue Polyommatus bellargus. Both butterfly species occur in calcareous grasslands and mainly depend on two plant species at our study site, the horseshoe vetch Hippocrepis comosa and bird’s-foot trefoil Lotus corniculatus. These plant species serve as nectar sources and larval host plants for the two butterfly species.

Methods

First, we assessed the occurrence of imagines and larvae of the two butterfly species and recorded various micro-habitat characteristics, like the number of flower buds of the two main host plants, the surrounding vegetation height, percentage of bare soil, availability of shadow, and the distance to and geographic direction of thickets at respective sites. In a second step we took high resolution aerial pictures from our study area using an unmanned aerial vehicle (drone). Based on these aerial pictures and the information on the larvae´s habitat preference from our field observations, we trained a habitat suitability model to identify micro-habitat structures suitable for larvae of the two butterfly species.

Results

We found that abundance of imagos is positively correlated with flower bud density of the two host plants. Low vegetation height and high proportion of bare soil (but not flower bud density) positively influence egg oviposition. The calculated habitat suitability models predict the occurrence of high quality larval habitats with high prediction power (AUC = 0.72).

Conclusions

This combined data set consisting of field observations, high resolution aerial pictures taken from an unmanned aerial vehicle, and models underline that (1) species with complex life cycles may request more than one habitat niche, depending its stage of development, and (2) high resolution aerial pictures taken from drones provide valuable background data to generate habitat suitability models—even on a micro scale but covering larger parts of a landscape.

     

Connectivity analysis as a tool for assessing restoration success

Context

Methods for measuring restoration success that include functional connectivity between species’ populations are rare in landscape ecology and restoration practices. We developed an approach that analyzes connectivity between populations of target species and their dispersal probabilities to assess restoration success based on easily accessible input data. Applying this method to landscape development scenarios can help optimize restoration planning.

Objectives

We developed an assessment for restoration success and restoration planning based on functional connectivity between species’ populations and spatially explicit scenarios. The method was used in a case study to test its applicability.

Methods

Based on data on available habitat, species’ occurrence and dispersal ranges, connectivity metrics and dispersal probabilities for target species are calculated using the software Conefor Sensinode. The metrics are calculated for scenarios that reflect possible changes in the landscape to provide a basis for future restoration planning. We applied this approach to floodplain meadows along the Upper Rhine for four plant species and three future scenarios.

Results

In the case study, habitats of the target species were poorly connected. Peucedanum officinale and Sanguisorba officinalis were more successful in recolonizing new habitats than Iris spuria and Serratula tinctoria. The scenarios showed that restoration of species-rich grassland was beneficial for dispersal of the target species. As expected in the agriculturally dominated study area, restoration of former arable land significantly increased dispersal probabilities.

Conclusions

In the case study, the developed approach was easily applicable and provided reasonable results. Its implementation will be helpful in decision-making for future restoration planning.

     

Empirical evaluation of the strength of interspecific competition in shaping small mammal communities in fragmented landscapes

Context

Theory predicts that habitat loss and fragmentation may have drastic consequences on species’ interactions. To date, however, little empirical evidence exists on the strength of interspecific competition in shaping animal communities in fragmented landscapes.

Objectives

Our aim was to measure the degree of ongoing competitive interference between species in fragmented landscapes. Our model system was the community of ground-dwelling rodents in deciduous woodlands in central Italy, composed of a habitat generalist species (Apodemus sylvaticus) and two forest specialists (Apodemus flavicollis and Myodes glareolus). Our objectives were to test whether species were segregated among forest patches and whether spatial segregation was determined by interspecific competition or habitat and resource availability.

Methods

We surveyed the populations inhabiting 29 woodland patches in a highly fragmented landscape using a capture-mark-recapture protocol, capturing >4500 individuals. First we modelled species’ distribution as a function of habitat, resource availability and landscape variables. The second stage of our analyses involved measuring the response of vital rate parameters (body mass, reproduction, survival, recruitment, population density) to competitor density.

Results

The relative distribution of species reflected a spatial segregation of habitat generalists and specialists according to habitat quality, cover and connectivity. Interspecific competition mainly affected individual level vital rates, whereas we found no substantial effects at the population level.

Conclusions

Competitive exclusion of specialist species by generalist species was occurring. However, when compared to other factors such as habitat connectivity and resource availability, interspecific competition played a relatively minor role in shaping the studied community.

     

Estimating landscape resistance from habitat suitability: effects of data source and nonlinearities

Context

Conservation corridors must facilitate long-distance dispersal movements to promote gene flow, prevent inbreeding, and allow animals to shift ranges with climate change. Least-cost models are used to identify areas that support long-distance movement. These models rely on estimates of landscape resistance, which are typically derived from habitat suitability.

Objectives

We examine two key steps in estimating resistance from habitat suitability: choosing a procedure to estimate habitat suitability, and choosing a transformation function to translate habitat suitability into resistance.

Methods

We used linear and nonlinear functions to convert three types of habitat suitability estimates (from expert opinion, resource selection functions, and step selection functions) into resistances for elk (Cervus canadensis) and desert bighorn sheep (Ovis canadensis nelsoni). We evaluated the resulting resistance maps on an independent set of observed long-distance, prospecting movements.

Results

A negative exponential function best described the relationship between resistance values and habitat suitability for desert bighorn sheep indicating long-distance movers readily travel through moderately-suitable areas and avoid only the least suitable habitat. For desert bighorn sheep, all three suitability estimates performed better than chance, and resource and step selection functions outperformed expert opinion. For elk, all three suitability estimates performed the same as chance.

Conclusions

When designing corridors to facilitate long-distance movements of mobile animals, we recommend transforming habitat suitability into resistance with a negative exponential function. Use of an exponential transformation means that larger fractions of the landscape offer low resistance, allowing greater flexibility in where a corridor is located.

     

Habitat amount and quality,not patch size,determine persistence of a woodland-dependent mammal in an agricultural landscape

Context

The classical theory of island biogeography explains loss of species in fragmented landscapes as an effect of remnant patch size and isolation. Recently this has been challenged by the habitat amount and habitat continuum hypotheses, according to which persistence in modified landscapes is related to total habitat amount rather than habitat configuration or the ability of species to use all habitats to varying degrees. Distinguishing between these theories is essential for effective conservation planning in modified landscapes.

Objective

Identify which factors of habitat type, amount and configuration predict the persistence of a keystone woodland specialist, the eastern bettong Bettongia gaimardi, in a fragmented landscape.

Method

In the Midlands region of Tasmania we carried out camera surveys at 62 sites in summer and winter. We included habitat and landscape features to model whether habitat amount or patch size and isolation influenced the presence of the eastern bettong, and to measure effects of habitat quality.

Results

Habitat amount within a 1 km buffer was a better predictor of occupancy than patch size and isolation. Occupancy was also affected by habitat quality, indicated by density of regenerating stems.

Conclusion

Our results support the habitat amount hypothesis as a better predictor of presence. For a species that is able to cross the matrix between remnant patches and utilise multiple patches, the island biogeography concept does not explain habitat use in fragmented landscapes. Our results emphasize the value of small remnant patches for conservation of the eastern bettong, provided those patches are in good condition.

     

Landscape and local effects on occupancy and densities of an endangered wood-warbler in an urbanizing landscape

Context

Golden-cheeked warblers (Setophaga chrysoparia), an endangered wood-warbler, breed exclusively in woodlands co-dominated by Ashe juniper (Juniperus ashei) in central Texas. Their breeding range is becoming increasingly urbanized and habitat loss and fragmentation are a main threat to the species’ viability.

Objectives

We investigated the effects of remotely sensed local habitat and landscape attributes on point occupancy and density of warblers in an urban preserve and produced a spatially explicit density map for the preserve using model-supported relationships.

Methods

We conducted 1507 point-count surveys during spring 2011–2014 across Balcones Canyonlands Preserve (BCP) to evaluate warbler habitat associations and predict density of males. We used hierarchical Bayesian models to estimate multiple components of detection probability and evaluate covariate effects on detection probability, point occupancy, and density.

Results

Point occupancy was positively related to landscape forest cover and local canopy cover; mean occupancy was 0.83. Density was influenced more by local than landscape factors. Density increased with greater amounts of juniper and mixed forest and decreased with more open edge. There was a weak negative relationship between density and landscape urban land cover.

Conclusions

Landscape composition and habitat structure were important determinants of warbler occupancy and density, and the large intact patches of juniper and mixed forest on BCP (>2100 ha) supported a high density of warblers. Increasing urbanization and fragmentation in the surrounding landscape will likely result in lower breeding density due to loss of juniper and mixed forest and increasing urban land cover and edge.

     

Species absence in developed landscapes: an experimental evaluation

Context

Conversion of landscapes is widely associated with loss of biodiversity. While there are several competing hypotheses for the local extinction of species in developed landscapes, experimental approaches are seldom applied to elucidating mechanisms.

Objectives

In this study, we focus on the habitat degradation hypothesis and predict that poor quality of relictual wetlands in developed landscapes contributes to the absence of wood frogs (Rana sylvatica = Lithobates sylvaticus) by decreasing their performance.

Methods

In a translocation experiment, we reared wood frog larvae within enclosures in seven ponds where they naturally occur and in five ponds in developed landscapes where they are absent. Premature pond drying precluded assessing performance in one present pond and one absent pond.

Results

Absent ponds were surrounded by upland buffers dominated by developed land covers while ponds with wood frog breeding populations were surrounded primarily by intact forest. Ponds were largely similar in their attributes. Survival and growth rate did not differ between pond types. Development tended to be slightly more rapid in some absent ponds perhaps related to higher water temperatures.

Conclusions

Despite the highly altered landscapes surrounding them, we find no evidence that absent wetlands provide inferior habitat for wood frog larval recruitment. Performance in absent ponds matched or exceeded that observed in present ponds implying that absence of this species may stem from influences mediated by the upland landscape. These results provide a caution to the typically unexamined presumption that relictual habitats in developed landscapes are degraded in their utility for wildlife.

     

Scale-specific habitat relationships influence patch occupancy: defining neighborhoods to optimize the effectiveness of landscape-scale grassland bird conservation

Context

Beyond the recognized importance of protecting large areas of contiguous habitat, conservation efforts for many species are complicated by the fact that patch suitability may also be affected by characteristics of the landscape within which the patch is located. Currently, little is known about the spatial scales at which species respond to different aspects of the landscape surrounding an occupied patch.

Objectives

Using grassland bird point count data, we describe an approach to evaluating scale-specific effects of landscape composition on patch occupancy.

Methods

We used data from 793 point count surveys conducted in idle and grazed grasslands across Wisconsin, USA from 2012 to 2014 to evaluate scale-dependencies in the response of grassland birds to landscape composition. Patch occupancy models were used to evaluate the relationship between occupancy and landscape composition at scales from 100 to 3000 m.

Results

Bobolink (Dolichonyx oryzivorus) exhibited a pattern indicating selection for grassland habitats in the surrounding landscape at all spatial scales while selecting against other habitats. Eastern Meadowlark (Sturnella magna) displayed evidence of scale sensitivity for all habitat types. Grasshopper Sparrow (Ammodramus savannarum) showed a strong positive response to pasture and idle grass at all scales and negatively to cropland at large scales. Unlike other species, patch occupancy by Henslow’s Sparrow (A. henslowii) was primarily influenced by patch area.

Conclusions

Our results suggest that both working grasslands (pasture) and idle conservation grasslands can play an important role in grassland bird conservation but also highlight the importance of considering species-specific patch and landscape characteristics for effective conservation.

     

Landscape genetics of the foundational salt marsh plant species black needlerush (<Emphasis Type="Italic">Juncus roemerianus</Emphasis> Scheele) across the northeastern Gulf of Mexico

Context

Common species important for ecosystem restoration stand to lose as much genetic diversity from anthropogenic habitat fragmentation and climate change as rare species, but are rarely studied. Salt marshes, valuable ecosystems in widespread decline due to human development, are dominated by the foundational plant species black needlerush (Juncus roemerianus Scheele) in the northeastern Gulf of Mexico.

Objectives

We assessed genetic patterns in J. roemerianus by measuring genetic and genotypic diversity, and characterizing population structure. We examined population connectivity by delineating possible dispersal corridors, and identified landscape factors influencing population connectivity.

Methods

A panel of 19 microsatellite markers was used to genotype 576 samples from ten sites across the northeastern Gulf of Mexico from the Grand Bay National Estuarine Research Reserve (NERR) to the Apalachicola NERR. Genetic distances (F_ST and D_ch) were used in a least cost transect analysis (LCTA) within a hierarchical model selection framework.

Results

Genetic and genotypic diversity results were higher than expected based on life history literature, and samples structured into two large, admixed genetic clusters across the study area, indicating sexual reproduction may not be as rare as predicted in this clonal macrophyte. Digitized coastal transects buffered by 500 m may represent possible dispersal corridors, and developed land may significantly impede population connectivity in J. roemerianus.

Conclusions

Results have important implications for coastal restoration and management that seek to preserve adaptive potential by sustaining natural levels of genetic diversity and conserving population connectivity. Our methodology could be applied to other common, widespread and understudied species.

     

A network model framework for prioritizing wetland conservation in the Great Plains

Context

Playa wetlands are the primary habitat for numerous wetland-dependent species in the Southern Great Plains of North America. Plant and wildlife populations that inhabit these wetlands are reciprocally linked through the dispersal of individuals, propagules and ultimately genes among local populations.

Objective

To develop and implement a framework using network models for conceptualizing, representing and analyzing potential biological flows among 48,981 spatially discrete playa wetlands in the Southern Great Plains.

Methods

We examined changes in connectivity patterns and assessed the relative importance of wetlands to maintaining these patterns by targeting wetlands for removal based on network centrality metrics weighted by estimates of habitat quality and probability of inundation.

Results

We identified several distinct, broad-scale sub networks and phase transitions among playa wetlands in the Southern Plains. In particular, for organisms that can disperse >2 km a dense and expansive wetland sub network emerges in the Southern High Plains. This network was characterized by localized, densely connected wetland clusters at link distances (h) >2 km but <5 km and was most sensitive to changes in wetland availability (p) and configuration when h = 4 km, and p = 0.2–0.4. It transitioned to a single, large connected wetland system at broader spatial scales even when the proportion of inundated wetland was relatively low (p = 0.2).

Conclusions

Our findings suggest that redundancy in the potential for broad and fine-scale movements insulates this system from damage and facilitates system-wide connectivity among populations with different dispersal capacities.

     

Long-term effects of managing for an endangered songbird on the heterogeneity of a fire-prone landscape

Context

Jack pine (Pinus banksiana)-dominated ecosystems of northern Lower Michigan are the primary breeding habitat for the federally endangered Kirtland’s warbler (Setophaga kirtlandii, KW). Historically, young stands used by KW were produced by stand-replacing wildfires, but fire suppression has necessitated the management of jack pine plantations for KW habitat since the 1970s. Effects of this long-term management on landscape age heterogeneity have previously not been quantified.

Objectives

We hypothesized that forest management has altered the spatial and temporal distribution of jack pine-dominated ecosystems beyond their historic range of variability.

Methods

By developing a diameter-age relationship for jack pine, we estimated ages of pre-European settlement trees found in General Land Office survey notes. We compared pre-European and current landscapes using geostatistical modeling of survey notes, and landscape metrics to quantify changes in pattern.

Results

Three KW management-based age classes (<20, 21–50, >50 years) are now more evenly distributed (31, 39, and 30 %, respectively) compared to the pre-European distribution (5, 19, 76 %) with little variability over time. Landscape metrics suggest the current landscape is younger and more fragmented than the pre-European landscape. These changes indicate restriction of the historic range of age variability, largely due to conversion of older jack pine stands to young KW habitat plantations.

Conclusions

Management has met KW population objectives, but has altered the temporal variability of the landscape’s age structure. Pre-European settlement patterns of stand-ages may provide a foundation for an ecosystem-based management plan for the region that supports both KW and the ecosystems upon which they depend.