The Ecology, Management and Monitoring of Wildlife Populations in Fragmented Landscapes - a Koala Case Study

Habitat fragmentation may adversely affect the ability of natural enemies to control pest outbreaks in agricultural landscapes by interfering with their search behavior and ability to aggregate in response to prey. We determined how landscape structure affected the ability of two ladybird beetles (Coleoptera: Coccinellidae) to track aphid populations in experimental landscapes that differed in the abundance and degree of fragmentation of red clover (Trifolium pratense). One coccinellid was a native species (Coleomegilla maculata Pallas) and the other (Harmonia axyridis Timberlake) was introduced specifically for the biological control of crop pests such as pea aphids (Acyrthosiphon pisum Harris; Homoptera: Aphididae). Landscape structure exhibited a threshold in lacunarity (a measure of interpatch distances) below 20% habitat, at which point clover patches became significantly more isolated. This threshold in landscape structure was mirrored by a similar threshold in the distribution of pea aphid populations. The distribution of the biocontrol agent, H. axyridis, tracked this threshold in aphid distribution, but the native coccinellid, C. maculata, was unable to do so in fragmented clover landscapes. Although C. maculata was a more active forager within clover cells, overall it was less mobile and moved significantly less among clover cells and between landscapes than H. axyridis, which may have contributed to its inability to track aphid populations in fragmented landscapes. The two coccinellids did not differ in their search success within fragmented landscapes, however, and it was only in clumped landscapes that H. axyridis maximized search success and foraged within clover cells that had 2.5–3 times more aphids than those in which C. maculata occurred. Thus, the potential of predators to control pest populations in fragmented landscapes may ultimately reflect the extent to which thresholds in landscape structure interfere with the aggregative response of predators. In this system, the aggregative response of coccinellids was more closely tied to thresholds in the distribution of clover than aphids. With its greater mobility, H. axyridis was more effective than the indigenous C. maculata at tracking aphids when they occurred at low patch occupancy (below the threshold in landscape structure), which is a requisite for successful biocontrol. If native insect predators are generally more sensitive to habitat fragmentation, greater reliance may be placed on the introduction of exotic species for biocontrol, which is not without economic cost and potential ecological impacts to native insect communities. Our study demonstrates that, in addition to economic thresholds, there are also ecological thresholds that must be surmounted if biocontrol measures are to be successful. In addition to enhancing vegetational diversity within agroecosystems, conservation biological control should also strive to mitigate fragmentation effects on natural enemies, especially if thresholds in landscape structure disrupt predator–prey interactions and compromise the efficacy of biocontrol programs.

Genetic stochasticity is considered an influencing factor in population survival (e.g. Shaffer 1981), hence population genetic theory and analysis are increasingly included in conservation biology (e.g. Hedrick & Miller 1992, Lande & Shannon 1996). Population genetic analyses in conservation biology have two major aims: (i) to demonstrate that genetic variability or single genetic variants are linked to fitness parameters such as viability, fecundity, and mating components (e.g. Richman et al. 1988), and (ii) to analyse the processes that cause the observed pattern of genetic variability. From a more practical point of view, analyses of population genetics may provide data that can be included in simulation models for the estimation of population viability and for the persistence of genetic variability in metapopulations under different environmental scenarios (Poethke et al. in press).KeywordsGene FlowDispersal AbilityConservation BiologyInsect PopulationFragmented LandscapeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

On improving the science and practice of riparian restoration

The 2 howler species that occur in southern Mexico, Alouatta palliata mexicana and Alouatta pigra are endangered, mainly as a result of habitat loss and fragmentation from human activity. Little is known about the gastrointestinal parasite communities affecting their populations, and lack of baseline information for populations of howler species in continuous forest habitats, makes evaluations of gastrointestinal parasite prevalence in populations in fragmented landscapes difficult. We report the results of a one-time broad survey of gastrointestinal parasites in fecal samples of individuals from several demographically stable populations of Alouatta palliata mexicana and A. pigra existing in continuous and/or protected forests. We further report similar data for populations of both species in human-fragmented landscapes. We detected 6 parasites for each howler monkey species, but only 3 of them (Trematode I, Controrchis biliophilus, Trypanoxyuris sp.) were common to both species. While parasitic prevalence in populations of both howler species was, in general, higher in the fragmented habitat than in continuous and/or protected forests. The difference is only marginally significant in Alouatta pigra. Some parasites (Coccidia and Strongylid) only appeared in populations in fragmented landscapes. Preliminary data suggest that adult males tended to have higher parasite prevalence values than those of adult females in both howler species. Parasite prevalence is associated to average group size, but not to population density in Alouatta pigra.

Many of the fungal pathogens that threaten agricultural and natural systems undergo wind-assisted dispersal. During turbulent wind conditions, long-distance dispersal can occur, and airborne spores are carried over distances greater than the mean. The occurrence of long-distance dispersal is an important ecological process, as it can drastically increase the extent to which pathogen epidemics spread across a landscape, result in rapid transmission of disease to previously uninfected areas, and influence the spatial structure of pathogen populations in fragmented landscapes. Since the timing of spore release determines the wind conditions that prevail over a dispersal event, this timing is likely to affect the probability of long-distance dispersal occurring. Using a Lagrangian stochastic model, we test the effect of seasonal and diurnal variation in the release of spores on wind-assisted dispersal. Spores released during the hottest part of the day are shown to be more likely to undergo long-distance dispersal than those released at other times. Furthermore, interactions are shown to occur between seasonal and diurnal patterns of release. These results have important consequences for further modelling of wind-assisted dispersal and the use of models to predict the spread of fungal pathogens and resulting population and epidemic dynamics.

The quality and extent of the ‘matrix’ in terrestrial fragmented landscapes may influence the persistence and behaviour of patch-associated fauna. Butterflies are a popular target group for fragmentation studies and represent an ideal assemblage to explore the impact and role of the matrix in patchy landscapes. To date, there has been no attempt to synthesise available research and assess the extent to which the matrix is included in studies of fragmented butterfly populations. Addressing this issue is important for improved understanding of habitat use in fragmented landscapes, and for the successful management and conservation of butterfly biodiversity. Our systematic review of 100 empirical research papers spans 50 years, and identifies how (and indeed if) the matrix is recognised in studies of butterfly populations in fragmented landscapes. We found that it was significantly more likely for studies not to include the matrix in their experimental design. This is of particular concern given 60 % of papers that excluded the matrix in their research did so in systems where the matrix was expected to contain resources of value for patch-associated species (as it was either a heterogeneous landscape or had similar structure to patches). Of the papers that did consider the matrix, 80 % (n = 24) reported a negative effect of the matrix on butterfly species and/or communities. Matrix effects may influence the survival and persistence of faunal groups in a world increasingly dominated by fragmented habitats. Our review suggests that future research should clearly define the matrix, and incorporate it in appropriate experimental designs.

Adaptive resource management is a learning-by-doing approach to natural resource management. Its effective practice involves the activation, completion, and regeneration of the management cycle while working toward achieving a flexible set of collaboratively identified objectives. This iterative process requires application of single-, double-, and triple-loop learning, to strategically modify inputs, outputs, assumptions, and hypotheses linked to improving policies, management strategies, and actions, along with transforming governance. Obtaining an appropriate balance between these three modes of learning has been difficult to achieve in practice and building capacity in this area can be achieved through an emphasis on reflexive learning, by employing adaptive feedback systems. A heuristic reflexive learning framework for adaptive resource management is presented in this manuscript. It is built on the conceptual pillars of the following: stakeholder driven adaptive feedback systems; strategic adaptive management (SAM); and hierarchy theory. The SAM Reflexive Learning Framework (SRLF) emphasizes the types, roles, and transfer of information within a reflexive learning context. Its adaptive feedback systems enhance the facilitation of single-, double-, and triple-loop learning. Focus on the reflexive learning process is further fostered by streamlining objectives within and across all governance levels; incorporating multiple interlinked adaptive management cycles; having learning as an ongoing, nested process; recognizing when and where to employ the three-modes of learning; distinguishing initiating conditions for this learning; and contemplating practitioner mandates for this learning across governance levels. The SRLF is a key enabler for implementing the management cycle, and thereby translating the theory of adaptive resource management into practice. It promotes the heuristics of adaptive management within a cohesive framework and its deployment guides adaptive resource management within and beyond typical single-loop learning, across all governance levels.

Traditional approaches to the study of fragmented landscapes invoke an island-ocean model and assume that the nonhabitat matrix surrounding remnant patches is uniform. Patch isolation, a crucial parameter to the predictions of island biogeography and metapopulation theories, is measured by distance alone. To test whether the type of interpatch matrix can contribute significantly to patch isolation, I conducted a mark-recapture study on a butterfly community inhabiting meadows in a naturally patchy landscape. I used maximum likelihood to estimate the relative resistances of the two major matrix types (willow thicket and conifer forest) to butterfly movement between meadow patches. For four of the six butterfly taxa (subfamilies or tribes) studied, conifer was 3-12 times more resistant than willow. For the two remaining taxa (the most vagile and least vagile in the community), resistance estimates for willow and conifer were not significantly different, indicating that responses to matrix differ even among closely related species. These results suggest that the surrounding matrix can significantly influence the "effective isolation" of habitat patches, rendering them more or less isolated than simple distance or classic models would indicate. Modification of the matrix may provide opportunities for reducing patch isolation and thus the extinction risk of populations in fragmented landscapes.

Habitat size, habitat isolation and habitat quality are regarded as the main determinants of butterfly occurrence in fragmented landscapes. To analyze the relationship between the occurrence of the butterflyCupido minimusand these factors, patch occupancy of the immature stages in patches of its host plantAnthyllisvulnerariawas studied in the nature reserve Hohe Wann in Bavaria (Germany). In 2001 and 2002, 82A.vulnerariapatches were surveyed for the presence ofC. minimus larvae.The occurrence was largely affected by the size of the food plant patches. In a habitat model that uses multiple logistic regression, the type of management and habitat connectivity are further determinants of species distribution. Internal and temporal validation demonstrate the stability and robustness of the developed habitat models. Additionally, it was proved that the colonization rate ofC. minimuswas significantly influenced by the distance to the next occupiedAnthyllispatch. Concerning long‐term survival of (meta‐) populations in fragmented landscapes, the results show that lower habitat quality may be compensated by higher connectivity between host plant patches.

The jaguar's patches: Viability of jaguar populations in fragmented landscapes

Traditional approaches to the study of fragmented landscapes invoke an island‐ocean model and assume that the nonhabitat matrix surrounding remnant patches is uniform. Patch isolation, a crucial parameter to the predictions of island biogeography and metapopulation theories, is measured by distance alone. To test whether the type of interpatch matrix can contribute significantly to patch isolation, I conducted a mark‐recapture study on a butterfly community inhabiting meadows in a naturally patchy landscape. I used maximum likelihood to estimate the relative resistances of the two major matrix types (willow thicket and conifer forest) to butterfly movement between meadow patches. For four of the six butterfly taxa (subfamilies or tribes) studied, conifer was 3–12 times more resistant than willow. For the two remaining taxa (the most vagile and least vagile in the community), resistance estimates for willow and conifer were not significantly different, indicating that responses to matrix differ even among closely related species. These results suggest that the surrounding matrix can significantly influence the “effective isolation” of habitat patches, rendering them more or less isolated than simple distance or classic models would indicate. Modification of the matrix may provide opportunities for reducing patch isolation and thus the extinction risk of populations in fragmented landscapes.

Abstract: A stochastic computer model was used to examine the effects of varying degrees of habitat fragmentation on the dynamics of a hypothetical population of forest‐interior bid. The primary demographic parameter that influenced the population's dynamics was fecundity, which varied as a function of how far a birds territory was from an ecological edge. As our model landscape became more fragmented the proportion of forest habitat that was near edges increased geometrically, and the population's overall fecundity dropped as a result. The model demonstrates that impaired reproduction in a fragmented landscape is, by itself a sufficient disruption of the population's dynamics to generate population declines and shifts in distribution similar to those observed in the fragmented forests of southern Wisconsin. Without immigration of recruits from other regions where reproduction is better, habitat‐interior populations in a severely fragmented landscape can become locally extinct.

Populations in fragmented landscapes experience reduced gene flow, lose genetic diversity over time and ultimately face greater extinction risk. Improving connectivity in fragmented landscapes is now a major focus of conservation biology. Designing effective wildlife corridors for this purpose, however, requires an accurate understanding of how landscapes shape gene flow. The preponderance of landscape resistance models generated to date, however, is subjectively parameterized based on expert opinion or proxy measures of gene flow. While the relatively few studies that use genetic data are more rigorous, frameworks they employ frequently yield models only weakly related to the observed patterns of genetic isolation. Here, we describe a new framework that uses expert opinion as a starting point. By systematically varying each model parameter, we sought to either validate the assumptions of expert opinion, or identify a peak of support for a new model more highly related to genetic isolation. This approach also accounts for interactions between variables, allows for nonlinear responses and excludes variables that reduce model performance. We demonstrate its utility on a population of mountain goats inhabiting a fragmented landscape in the Cascade Range, Washington.

Non-additive effects of pollen limitation and self-incompatibility reduce plant reproductive success and population viability

Ecosystem fragmentation results in major changes in several environmental and biotic parameters that affect the ability of plant populations to persist. All stages of the plant life cycle may be influenced in either negative or positive ways by the changed biophysical settings caused by fragmentation and associated changes in the surrounding landscape. This may result in plant populations being lost or significantly reduced from patches of native vegetation, leading to the need for active management intervention. This intervention may include management of threatening processes, reversal of ecosystem degradation, or the reintroduction of plants of species that have been lost from an area. These management actions range from preventative management through to active restoration. In the present paper I explore the question of whether there is a limit to the degree of intervention that is desirable in conservation terms, beyond which we are no longer conserving but rather cultivating and gardening, i.e. creating an artificial and potentially unsustainable system. I discuss this question in relation to management of remnant vegetation in urban and agricultural settings and suggest that a careful mix of species-based and process-based management is required for us to succeed in the goal of biodiversity conservation in fragmented landscapes.