Papers by Kate Helmstedt
Threatened species with reduced and fragmented habitats can be reintroduced into their historical... more Threatened species with reduced and fragmented habitats can be reintroduced into their historical ranges to establish new populations. Multiple sites might be an option for reintroductions; therefore, managers must determine when to open sites (e.g. establish infrastructure and improve conditions), release individuals into those sites, and eventually cease releases. Careful planning of this schedule, incorporating the cost of actions, is imperative at the outset of a program. To address this challenge , we consider a reintroduction plan under different cost scenarios for three potential reintroduction sites. In particular, we investigate the implications of having either no ongoing site-management cost, a financial ongoing site-management cost, or a demographic cost of continuous releases. We couple population and management models to find a schedule that maximizes total abundance over time of bridled nail-tail wallaby Onychogalea fraenata (released in fixed numbers each breeding season from a stable source population) using stochastic dynamic programming. We find that the type of ongoing cost influences the structure of the optimal schedule. If active release sites cost nothing to maintain, there is no incentive to cease releases. In that case, the optimal schedule is to open sites sequentially , then release individuals to the smallest active population for the entire length of the program. A financial cost for managing active sites alters this result; once all sites are open and have populations of a critical threshold size, sites should be closed sequentially. A higher mortality rate (demographic cost) at active compared to inactive sites completely changes the structure of the optimal strategy. Instead of opening all sites in the first few management stages, only one site should be active any time to reduce the demographic impact of releases. Our general results provide a guide for planning future reintroduction programs and illustrate the importance of categorizing and understanding ongoing costs for reintroduction planning.
Damage and mortality patterns in young mixed conifer plantations following prescribed fires in the Sierra Nevada, California
Forest Ecology and Management, 2016
Abiotic and biotic interactions determine whether increased colonization is beneficial or detrimental to metapopulation management
Theoretical population biology, Jan 3, 2016
Increasing the colonization rate of metapopulations can improve persistence, but can also increas... more Increasing the colonization rate of metapopulations can improve persistence, but can also increase exposure to threats. To make good decisions, managers must understand whether increased colonization is beneficial or detrimental to metapopulation persistence. While a number of studies have examined interactions between metapopulations, colonization, and threats, they have assumed that threat dynamics respond linearly to changes in colonization. Here, we determined when to increase colonization while explicitly accounting for non-linear dependencies between a metapopulation and its threats. We developed patch occupancy metapopulation models for species susceptible to abiotic, generalist, and specialist threats and modeled the total derivative of the equilibrium proportion of patches occupied by each metapopulation with respect to the colonization rate. By using the total derivative, we developed a rule for determining when to increase metapopulation colonization. This rule was applie...
Adding and subtracting species: the mathematics of eradication and reintroduction for conservation
1. Many highly diverse island ecosystems across the globe are threatened by invasive species. Era... more 1. 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 success aided by geographical isolation and increasing knowledge of eradication techniques. There have been many attempts to prioritize islands for invasive species eradica-tion; 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. 2. 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). 3. 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 prioritiza-tion method outperforms simpler methods for almost 80% of the budgets considered. 4. 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%. 5. Synthesis and applications. Substantially higher ecological benefits for threatened species can be achieved for no extra cost if conservation planners relax the assumption that eradica-tion projects must target all invasives on an island. It is more efficient to prioritize portfolios of eradication actions rather than islands.
Fences that exclude alien invasive species are used to reduce predation pressure on reintroduced ... more 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 costefficiency 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.
1. The conservation of many threatened species can be advanced by the eradication of alien invasi... more 1. The conservation of many threatened species can be advanced by the eradication of alien invasive animals from islands. However, island eradications are an expensive, difficult and uncertain undertaking. An increasingly common eradication strategy is the construction of 'interior fences' to partition islands into smaller, independent eradication regions that can be treated sequentially or concurrently. Proponents argue that, while interior fences incur substantial up front construction costs, they reduce overall eradication costs. However, this hypothesis lacks an explicit theoretical or empirical justification. 2. We formulate a general theory that relates the number of interior fences to the magnitude and variation of the economic cost of island eradication. We use this theory to explore the conditions under which interior fences represent a defensible management strategy, under cost and risk minimisation objectives. We then specifically consider the forthcoming eradication of cats Felis catus from Dirk Hartog Island, Western Australia, by parameterising our general theory using published data on the cost and success of previous projects. 3. Our results predict that under a wide range of reasonable conditions, interior fences can reduce the expected cost of a successful invasive alien animal eradication from large islands. On Dirk Hartog Island, interior fences will marginally reduce eradication costs, with two fences reducing expected costs by 3%. Interior fences have a much more substantial effect on the variability of eradication costs: two fences reduce the width of the 95% confidence bounds by more than one-third and halve the size of the average project cost overrun/underrun. 4. Our results reveal that the construction of interior fences is a defensible management strategy for eradicating alien invasive species from islands. However, the primary benefit of interior fences will be risk management, rather than a reduction in expected project costs.
Other articles, not peer reviewed by Kate Helmstedt
In semi-arid regions, like the Western United States, the intertwined stressors of climate variab... more In semi-arid regions, like the Western United States, the intertwined stressors of climate variability, persistent waste, continued pollution and shifting demographics are creating trilemmas in linked food, energy, and water (FEW) systems. The effects of these trilemmas are environmental, economic, and social. For example, on-going drought in California has reduced the availability of water for both renewable hydropower and agriculture. The resulting water-use trade-offs have left fields fallow, increased energy and food prices, and depleted groundwater supplies. To develop the science, technology, and policy to resolve trilemmas in FEW systems, University of California at Berkeley hosted the National Science Foundation funded Developing Intelligent Food, Energy, and Water Systems Workshop (DIFEWS) on September 28-29, 2015. The workshop brought together investigators in the physical, natural, computer, and social sciences, along with engineers, economists, policy-makers, and practitioners from diverse backgrounds.
The workshop identified three key challenges for FEW systems in California and beyond, discussed in this whitepaper.
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Papers by Kate Helmstedt
Other articles, not peer reviewed by Kate Helmstedt
The workshop identified three key challenges for FEW systems in California and beyond, discussed in this whitepaper.