[Show abstract][Hide abstract] ABSTRACT: Many highly diverse island ecosystems across the globe are threatened by invasive species. Eradications of invasive mammals from islands are being attempted with increasing frequency, with their success aided by geographical isolation and increasing knowledge of eradication techniques. There have been many attempts to prioritize islands for invasive species eradication; however, these coarse methods all assume managers are unrealistically limited to a single action on each island: either eradicate all invasive mammals, or do nothing. We define a prioritization method that broadens the suite of actions considered, more accurately representing the complex decisions facing managers. We allow the opportunity to only eradicate a subset of invasive mammals from each island, intentionally leaving some invasive mammals on islands. We consider elements often omitted in previous prioritization methods, including feasibility, cost, and complex ecological responses (i.e. trophic cascades). Using a case study of Australian islands, we show that for a fixed budget this method can provide a higher conservation benefit across the whole group of islands. Our prioritization method outperforms simpler methods for almost 80% of the budgets considered. On average, by relaxing the restrictive assumption that an eradication attempt must be made for all invasives on an island, ecological benefit can be improved by 27%. Synthesis and applications. Substantially higher ecological benefits for threatened species can be achieved for no extra cost if conservation planners relax the assumption that eradication projects must target all invasives on an island. It is more efficient to prioritize portfolios of eradication actions, rather than islands. This article is protected by copyright. All rights reserved.
Full-text · Article · Dec 2015 · Journal of Applied Ecology
[Show abstract][Hide abstract] ABSTRACT: Ecological systems are dynamic and policies to manage them need to respond to
that variation. However, policy adjustments will sometimes be costly, which
means that fine-tuning a policy to track variability in the environment very
tightly will only sometimes be worthwhile. We use a classic fisheries
management question -- how to manage a stochastically varying population using
annually varying quotas in order to maximize profit -- to examine how costs of
policy adjustment change optimal management recommendations. Costs of policy
adjustment (here changes in fishing quotas through time) could take different
forms. For example, these costs may respond to the size of the change being
implemented, or there could be a fixed cost any time a quota change is made. We
show how different forms of policy costs have contrasting implications for
optimal policies. Though it is frequently assumed that costs to adjusting
policies will dampen variation in the policy, we show that certain cost
structures can actually increase variation through time. We further show that
failing to account for adjustment costs has a consistently worse economic
impact than would assuming these costs are present when they are not.
[Show abstract][Hide abstract] ABSTRACT: Management strategies to reduce the risks to human life and property from wildfire commonly involve burning native vegetation. However, planned burning can conflict with other societal objectives such as human health and biodiversity conservation. These conflicts are likely to intensify as fire regimes change under future climates and as growing human populations encroach further into fire-prone ecosystems. Decisions about managing fire risks are therefore complex and warrant more sophisticated approaches than are usually applied. We demonstrate a multi-criteria decision making approach (MCDA) with potential to improve fire management outcomes. For a case study from a highly populated, biodiverse and flammable wildland-urban interface, we considered the effects of 22 planned burning options on eight objectives: house protection, water quality, carbon emissions/human health, and five distinct species types. MCDA identified a small number of management options (burning forest adjacent to houses) that performed well for most objectives, but not for one species-type (arboreal mammal) and water-quality. While MCDA made this conflict explicit, resolution of the problem depended on the weighting assigned to each objective. Additive weighting of criteria sacrificed the arboreal mammal and water quality for gains in other objectives. Multiplicative weighting identified scenarios that avoided poor outcomes for any objective; important for avoiding potentially irreversible biodiversity losses. To distinguish reliably among management options, future work should focus on reducing uncertainty in outcomes across a range of objectives. Considering management actions that have more predictable outcomes than landscape fuel management will be important. Our study demonstrates that, where data are adequate, MCDA can support decision-making in the complex and often conflicted area of fire management. This article is protected by copyright. All rights reserved
No preview · Article · Jul 2015 · Conservation Biology
[Show abstract][Hide abstract] ABSTRACT: When protected areas reduce threats within their boundaries, they often displace a portion of these threats into adjacent areas through a process known as 'leakage', undermining conservation objectives. Using theoretical models and a case study of terrestrial mammals in Indonesia, we develop the first theoretical explanation of how leakage impacts conservation actions, and highlight conservation strategies that mitigate these impacts. Although leakage is a socio-economic process, we demonstrate that its negative impacts are also affected by the distribution of species, with leakage having larger impacts in landscapes with homogeneous distribution of species richness. Moreover, leakage has a greater negative effect when conservation strategies are implemented opportunistically, even creating the potential for perversely negative consequences from protected area establishment. Leakage thereby increases the relative benefits of systematic conservation planning over opportunism, especially in areas with high leakage and heterogeneously distributed species. Although leakage has the potential to undermine conservation actions, conservation planning can minimize this risk.
[Show abstract][Hide abstract] ABSTRACT: Islands are global hotspots of both biodiversity and extinction. Invasive species are a primary threat, and the majority of islands have been invaded by more than one. Multispecies eradications are essential for conserving the biodiversity of these islands, but experience has shown that eradicating species at the wrong time can be disastrous for endemic species.Managers not only have to decide how to eradicate each invasive species, they need to determine when to target each species, and how to control multiple species with a limited budget. We use dynamic control theory to show that, when resources are limited, species should be eradicated in a particular order (an eradication schedule). We focus on a common invaded island ecosystem motif, where one invasive predator consumes two prey species (one endemic, one invasive), and managers wish to eradicate both invasives while ensuring the persistence of the endemic species. We identify the optimal eradication schedule for this entire class of problem. To illustrate the application of our solution, we also analyse a particular case study from California's Channel Islands.For any island ecosystem that shares this motif, managers should begin by allocating all of their resources towards invasive predator control. Only later should resources be shifted towards controlling the invasive prey. This shift should ideally be gradual, but an abrupt shift is very close to optimal. The Channel Islands case study confirms these findings. Targeting both species simultaneously is substantially suboptimal.We reach the robust conclusion that the same eradication schedule should be applied to any island with this ecosystem motif, even if the ecosystem contains different species to the Channel Islands case study.Synthesis and applications: Although very numerous, the world's invaded island ecosystems could be described by a limited range of invaded ecosystem motifs. By calculating robust optimal eradication schedules for each motif, the approach defined in this study could offer rapid decision-support for a large number of future conservation projects where specific data are scarce.This article is protected by copyright. All rights reserved.
Full-text · Article · Mar 2015 · Journal of Applied Ecology
[Show abstract][Hide abstract] ABSTRACT: Conservation outcomes are principally achieved through the protection of intact habitat or the restoration of degraded habitat. Restoration is generally considered a lower priority action than protection because protection is thought to provide superior outcomes, at lower costs, without the time delay required for restoration. Yet while it is broadly accepted that protected intact habitat safeguards more biodiversity and generates greater ecosystem services per unit area than restored habitat, conservation lacks a theory that can coherently compare the relative outcomes of the two actions. We use a dynamic landscape model to integrate these two actions into a unified conservation theory of protection and restoration. Using nonlinear benefit functions, we show that both actions are crucial components of a conservation strategy that seeks to optimise either biodiversity conservation or ecosystem services provision. In contrast to conservation orthodoxy, in some circumstances, restoration should be strongly preferred to protection. The relative priority of protection and restoration depends on their costs and also on the different time lags that are inherent to both protection and restoration. We derive a simple and easy-to-interpret heuristic that integrates these factors into a single equation that applies equally to biodiversity conservation and ecosystem service objectives. We use two examples to illustrate the theory: bird conservation in tropical rainforests and coastal defence provided by mangrove forests.
[Show abstract][Hide abstract] ABSTRACT: Protected area networks are designed to restrict anthropogenic pressures in areas of high biodiversity. Resource users respond by seeking to replace some or all of the lost resources from locations elsewhere in the landscape. Protected area networks thereby perturb the pattern of human pressures by displacing extractive effort from within protected areas into the broader landscape, a process known as leakage. The negative effects of leakage on conservation outcomes have been empirically documented and modeled using homogeneous descriptions of conservation landscapes. Human resource use and biodiversity vary greatly in space, however, and a theory of leakage must describe how this heterogeneity affects the magnitude, pattern, and biodiversity impacts of leakage. We combined models of household utility, adaptive human foraging, and biodiversity conservation to provide a bioeconomic model of leakage that accounts for spatial heterogeneity. Leakage had strong and divergent impacts on the performance of protected area networks, undermining biodiversity benefits but mitigating the negative impacts on local resource users. When leakage was present, our model showed that poorly designed protected area networks resulted in a substantial net loss of biodiversity. However, the effects of leakage can be mitigated if they are incorporated ex-ante into the conservation planning process. If protected areas are coupled with nonreserve policy instruments such as market subsidies, our model shows that the trade-offs between biodiversity and human well-being can be further and more directly reduced.
Full-text · Article · Dec 2014 · Conservation Biology
[Show abstract][Hide abstract] ABSTRACT: Fences that exclude alien invasive species are used to reduce predation pressure on reintroduced threatened wildlife. Planning these continuously managed systems of reserves raises an important extension of the Single Large or Several Small (SLOSS) reserve planning framework: the added complexity of ongoing management. We investigate the long-term cost-efficiency of a single large or two small predator exclusion fences in the arid Australian context of reintroducing bilbies Macrotis lagotis, and we highlight the broader significance of our results with sensitivity analysis. A single fence more frequently results in a much larger net cost than two smaller fences. We find that the cost-efficiency of two fences is robust to strong demographic and environmental uncertainty, which can help managers to mitigate the risk of incurring high costs over the entire life of the project.
Full-text · Article · Oct 2014 · Ecological Applications
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Choosing effective management strategies for invasive species is a global challenge. The invasive species problem comprises a huge number of species, and modelling every invasive species to determine appropriate management strategies is impractical. There is a pressing need to provide general guidelines for invasive species managers that can easily be applied in a range of locations and scenarios. We use a reaction-diffusion model and optimal control theory to determine optimal management strategies in a range of invasive species scenarios. We demonstrate how to adjust control effort through time for an island eradication; how control efforts should vary through space around high-value conservation assets; and how to vary control efforts through space and time to eradicate a new invasion. By estimating relatively few parameters, our solutions give managers a strong platform on which to base strategic decisions. Our methods can also be applied to specific situations, and we demonstrate this with a case study of a tropical fire ant (Solenopsis geminata) eradication on Ashmore Reef.
Our results show a very clear relationship between population spread rate, population growth rate and the diminishing returns of control effectiveness. For island eradications we find that it is optimal to start with a relatively small amount of control and increase through time. The optimal eradication time depends on growth rate and the diminishing returns parameter. If a population grows quickly or large control efforts can be applied effectively, then it is best to eradicate it quickly. Otherwise, longer eradications result in lower overall costs. For spatial suppression around high conservation assets, the most important quantity is the ratio of the spread and growth rates. If the ratio is large, then it is optimal to target a large section of the surrounding landscape, while if the ratio is small it is best to focus control efforts near the conservation asset. Controlling a spreading invasion incorporates principles from both temporal eradication and spatial control problems. Control efforts should initially be focussed at the main infestation and then increased in the surrounding region through time.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
The eradication of invasive species from uninhabited islands presents an immense opportunity for conservation. Islands hold a disproportionate percent of global biodiversity, there has been historically less human intervention on island ecosystems, and the native species of islands have unique, divergent evolutionary histories. Despite this, a high proportion of animal extinctions have occurred on islands due to invasive vertebrates. Unfortunately, island conservation actions are unusually expensive, so it is imperative that the limited finances available are spent on eradications that maximise conservation benefits. Therefore to ensure investments in invasive eradication are spent wisely, the cost-efficiency and feasibility of actions must be considered transparently and defensibly, with a rational treatment of uncertainties.
We propose a general method for prioritizing the eradication of multiple invasive species across multiple islands for a fixed budget. Rather than focusing on islands as management units, this method prioritises portfolios of eradication actions targeting different subsets of invasive species. This better reflects the variety of options available to managers, and the range of ecological dynamics that can result from perturbing an insular system.
We present a case study prioritization of 23 potential action packages on four Australian islands: Macquarie, Tasman, Faure and Hermite Islands. By including the possibility to only eradicate a subset of invasive species on each island, we find that there are measurable increases in the total expected conservation benefit. The optimal prioritization action for some budgets is to leave some invasive species present on one of the islands (often mice due to the high cost and low feasibility of eradication) in favour of eradicating a more ecologically harmful invasive species on another island.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Unsustainable exploitation of the oceans has led to widespread degradation of marine ecosystems. In order to maintain the primary benefits humans derive from the sea, namely food supply and biodiversity that generates other ecosystem services, the ocean is divided into three general management regimes: open–access areas with no restrictions, managed areas that control aspects of gear and fishing effort that damage habitat, and reserved or protected areas that prohibit all extractive uses. Using a theoretical example of a fish stock that depends on habitat type, we explore the conditions under which is it better to spare the sea, by investing more in no take marine reserves, to share the sea by investing in gear management to maintain habitat quality over a larger area, or a mixed strategy. We model the fraction of the seascape in each management regime given a fixed budget and a minimum food supply. Our objective is to create a plausible model with a simple analytic answer for the purpose of allowing people to choose broad policy options.
We explored the range of parameters where no-take marine reserves may be favoured over habitat protection with fishing and vice versa. The relative costs of no-take reserves vs. habitat protection, the growth rate of the fish population, the effectiveness of habitat protection and the amount of self-recruitment all influence this decision. For example, preliminary results suggest that intermediate levels of self-recruitment favour a mixed strategy of some no-take reserves and habitat management areas. Obviously, when the cost of reserving area increases in relation to managing an area to reduce habitat loss, we prefer a management regime that protects habitat. We are working on a simple rule of thumb that determines the optimal management strategy given our constraints.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Much ecological theory underpinning studies in ecosystem management and life history evolution draws on a body of mathematics known as optimal control. In one set of applications, ecosystems managers are assumed to be seeking ‘optimal’ decisions over how to allocate and manage natural resources; in the other, an ‘optimal’ behavior or phenotype is predicted given the particular ecological conditions that an organism will face. In both situations, the underlying ecological systems involved can be noisy, high dimensional and nonlinear; they also vary over multiple space and time scales and are only ever observed imperfectly. However, much of this richness is assumed away in theoretical ecology in a quest to identify optimal solutions. Instead, what is needed is a theoretical approach that embraces the messy complexity of ecological questions without giving up on the optimizers’ drive to find effective management or life history strategies.
We will present a series of such approaches that together offer an alternative to traditional optimal control. When taken together, we refer to these alternatives as ‘pretty darn good’ control. We will illustrate pretty darn good control through a series of applications in marine ecology and marine ecosystem management.
Some recurring lessons from our efforts to apply pretty darn good control to ecological questions include that
i) behaviors that can seem suboptimal when compared to simplified problem formulations might instead be rational and effective once a fuller representation of the relevant optimization problem is considered.
ii) the detailing of how you represent constraints and limitations on the choice sets that individuals face is very important for obtaining sensible predictions from your model.
iii) only some sources of ecological variation need to be reflected in a pretty darn good life history or management strategy and only some entry-points of uncertainty need to be resolved to deliver effective performance.
iv) and finally, when developing a strategy that can respond to ecological variation, a small amount of responsiveness earns big pay-offs, but finessing further offers comparatively little gain.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Ecological systems are dynamic and policies to manage them need to respond to that variation. However, policy adjustments will sometimes be costly, which means that fine-tuning a policy to track variability in the environment very tightly will only sometimes be worthwhile. We use a classic fisheries management question – how to manage a stochastically varying population using annually varying quotas in order to maximize profit - to examine how costs of policy adjustment change optimal
management recommendations. Costs of policy adjustment (here changes in fishing quotas through time) could take different forms. For example, these costs may respond to the size of the change being implemented or there could be a fixed cost any time a quota change is made.
We show how different forms of policy costs have contrasting implications for optimal policies. While some types of cost act to smooth out variation in quotas and stock sizes, as one might have expected, others can actually increase variation in stock sizes and quotas through time. We also show that the potential economic impact on the fishery of managers assuming policy adjustment costs are present when in fact they are absent is much smaller than the impact of managers assuming such costs are absent if they are present.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods:
Conservation management decisions are often implemented to reflect human scales, rather than the scale of the relevant ecological dynamics. Research frequently points out the loss in efficiency that results from this scale mismatch. However, the scale of management is influenced by social, economic and political constraints on management actors; by the higher implementation costs of spatially-variable management plans; and by the divergent objectives of the actors in different regions. The critical question is not whether conservation benefits would increase if management were planned at ecological scales, but whether such benefits are sufficient to justify the cost of alignment.
Fishery management often has strong spatial components, with harvest quotas, gear restrictions, and marine protected areas applying to specific locations. Such spatial management decisions are generally implemented at spatial scales that have a coarser resolution than the underlying population dynamics. We use a spatially-explicit bioeconomic metapopulation model of a line fishery within the Great Barrier Reef Marine Park to explore the relationship between scale mismatches and management efficiency, and to quantify the benefits that result from an increased alignment between management actions and key ecological scales. In this system, the management scales are defined by the boundaries of total allowable catch regions, while the important ecological scales are defined by complex biophysical connectivity between reef populations.
Given a particular scale of management (defined by the number of separate catch quotas), our approach identifies (1) the distribution of harvest efforts, and (2) the location of management boundaries, that maximise the profitability of the fished metapopulation. Assessing a range of management scales allows us to characterise the relationship between the size of the mismatch between ecological and management scales, and the magnitude of the resulting inefficiency. We further contrast the locations of the resulting boundaries with natural ecological boundaries created by the dispersal network that connects the reef populations.
Decreasing the mismatch between management and ecological scales yields only diminishing efficiency returns, while incurring accelerating transaction costs. The result is that management efficiency is maximised by a management scale (or alternatively, a management resolution) that is much larger than the underlying ecological process: effectively, an optimal scale mismatch.
[Show abstract][Hide abstract] ABSTRACT: Growing threats and limited resources have always been the financial realities of biodiversity conservation. As the conservation sector has matured, however, the accountability of conservation investments has become an increasingly debated topic, with two key topics being driven to the forefront of the discourse: understanding how to manage the risks associated with our conservation investments and demonstrating that our investments are making a difference through evidence-based analyses. A better understanding of the uncertainties associated with conservation decisions is a central component of managing risks to investments that is often neglected. This focus issue presents both theoretical and applied approaches to quantifying and managing risks. Furthermore, transparent and replicable approaches to measuring impacts of conservation investments are noticeably absent in many conservation programs globally. This focus issue contains state of the art conservation program impact evaluations that both demonstrate how these methods can be used to measure outcomes as well as directing future investments. This focus issue thus brings together current thinking and case studies that can provide a valuable resource for directing future conservation investments.
Full-text · Article · Aug 2014 · Environmental Research Letters
[Show abstract][Hide abstract] ABSTRACT: A range of mathematical models has been developed to infer whether a species is extinct based on a sighting record. Although observations have variable reliability, current methods for detecting extinction do not differentiate observation qualities.
A more suitable approach would consider certain and uncertain sightings throughout the sighting period. We consider a small population system, meaning we assume sighting rates are constant and the population is not declining. Based on such an assumption, we develop a Bayesian method that assumes that certain and uncertain sightings occur independently and at uniform rates. These two types of sightings are connected by a common extinction date. Several rates of false sightings can be calculated to differentiate between observation types. Prior rates of false and true sightings, as well as a prior probability that the species is extant, are included. The model is implemented in OpenBugs, which uses Markov chain Monte Carlo (MCMC).
Based on records of variable reliability, we estimate the probability that the following species are extinct: Caribbean seal Monachus tropicalis, grey, black-footed ferret Mustela nigripes, Audubon & Bachman, greater stick-nest rat Leporillus conditor, Sturt, and lesser stick-nest rat Leporillus apicalis, Gould. As further examples, Birdlife International provided the sighting records for the Alaotra grebe Tachybaptus rufolavatus, Delacour, Jamaica petrel Pterodroma caribbaea, Carte, and Pohnpei mountain starling Aplonis pelzelni, Finsch, with prior probabilities for extinction. The results are compared with existing methods, which ignore uncertain sightings. We find that including uncertain sightings can considerably change the probability that the species is extant, in either direction. However, in our examples, including the quality of the uncertain sighting made little difference. When we ignore uncertain sightings, our results agree with existing methods, especially when the last sighting was near the end of the sighting period.
Synthesis and applications. Estimating the probability that a species is extinct based on sighting records is important when determining conservation priorities and allocating available resources into management activities. Having a model that allows for certain and uncertain observations throughout the sighting period better accommodates the realities of sighting quality, providing a more reliable basis for decision-making.
No preview · Article · Feb 2014 · Journal of Applied Ecology