Optimizing Dispersal Corridors for the Cape Proteaceae Using Network Flow

AT&T Labs-Research, 180 Park Avenue, Florham Park, New Jersey 07932, USA.
Ecological Applications (Impact Factor: 4.09). 08/2008; 18(5):1200-11. DOI: 10.1890/07-0507.1
Source: PubMed


We introduce a new way of measuring and optimizing connectivity in conservation landscapes through time, accounting for both the biological needs of multiple species and the social and financial constraint of minimizing land area requiring additional protection. Our method is based on the concept of network flow; we demonstrate its use by optimizing protected areas in the Western Cape of South Africa to facilitate autogenic species shifts in geographic range under climate change for a family of endemic plants, the Cape Proteaceae. In 2005, P. Williams and colleagues introduced a novel framework for this protected area design task. To ensure population viability, they assumed each species should have a range size of at least 100 km2 of predicted suitable conditions contained in protected areas at all times between 2000 and 2050. The goal was to design multiple dispersal corridors for each species, connecting suitable conditions between time periods, subject to each species' limited dispersal ability, and minimizing the total area requiring additional protection. We show that both minimum range size and limited dispersal abilities can be naturally modeled using the concept of network flow. This allows us to apply well-established tools from operations research and computer science for solving network flow problems. Using the same data and this novel modeling approach, we reduce the area requiring additional protection by a third compared to previous methods, from 4593 km2 to 3062 km , while still achieving the same conservation planning goals. We prove that this is the best solution mathematically possible: the given planning goals cannot be achieved with a smaller area, given our modeling assumptions and data. Our method allows for flexibility and refinement of the underlying climate-change, species-habitat-suitability, and dispersal models. In particular, we propose an alternate formalization of a minimum range size moving through time and use network flow to achieve the revised goals, again with the smallest possible newly protected area (2850 km2). We show how to relate total dispersal distance to probability of successful dispersal, and compute a trade-off curve between this quantity and the total amount of extra land that must be protected.

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    • "All rights reserved. (e.g., Phillips et al. 2008). There is a pressing need for methods that guide the design of networks that facilitate the movements of organisms at multiple spatial scales. "
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    ABSTRACT: 1.Biodiversity conservation in landscapes undergoing climate and land-use changes requires designing multi-purpose habitat networks that connect the movements of organisms at multiple spatial scales. Short-range connectivity within habitat networks provides organisms access to spatially distributed resources, reduces local extinctions, and increases re-colonization of habitat fragments. Long-range connectivity across habitat networks facilitates annual migrations and climate-driven range shifts.2.We present a method for identifying a multi-purpose network of forest patches that promotes both short and long-range connectivity. Our method uses both graph-theoretic analyses that quantify network connectedness and circuit-based analyses that quantify network traversability as the basis for identifying spatial conservation priorities on the landscape.3.We illustrate our approach in the agroecosystem, bordered by the Laurentian and Appalachian mountain ranges, that surrounds the metropolis of Montreal, Canada. We established forest conservation priorities for the Ovenbird, a Neotropical migrant, sensitive to habitat fragmentation that breeds in our study area. All connectivity analyses were based on the same empirically informed resistance surface for Ovenbird but habitat pixels that facilitated short- and long-range connectivity requirements had low spatial correlation. The trade-off between connectivity requirements in the final ranking of conservation priorities showed a pattern of diminishing returns such that beyond a threshold, additional conservation of long-range connectivity had decreased effectiveness on the conservation of short-range connectivity. Highest conservation priority was assigned to a series of stepping stone forest patches across the study area that promote traversability between the bordering mountain ranges and to a collection of small forest fragments scattered throughout the study area that provide connectivity within the agroecosystem.4.Landscape connectivity is important for the ecology and genetics of populations threatened by climate change and habitat fragmentation. Our method has been used to conserve two critical dimensions of connectivity for a single species but it is designed to incorporate a variety of connectivity requirements for many species. Our approach can be tailored to local, regional, and continental conservation initiatives to protect essential species movements that will allow biodiversity to persist in a changing climate.This article is protected by copyright. All rights reserved.
    Full-text · Article · Sep 2015 · Methods in Ecology and Evolution
    • "Thus, studies have begun to try to anticipate projected impacts of climate change on species distributions and to integrate those shifts into the conservation-planning process (e.g., Phillips et al. 2008). One potentially promising approach to addressing climate change in the conservation-planning process involves selecting areas to protect biodiversity based on the distribution of abiotic conditions (e.g., climate, geology , topography) (Hunter et al. 1988; Mackey et al. 1988; Kirkpatrick & Brown 1994). "
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    ABSTRACT: Geodiversity has been used as a surrogate for biodiversity when species locations are unknown, and this utility can be extended to situations where species locations are in flux. Recently, scientists have designed conservation networks that aim to explicitly represent the range of geophysical environments, identifying a network of physical stages that could sustain biodiversity while allowing for change in species composition in response to climate change. Because there is no standard approach to designing such networks, we compiled 8 case studies illustrating a variety of ways scientists have approached the challenge. These studies show how geodiversity has been partitioned and used to develop site portfolios and connectivity designs; how geodiversity-based portfolios compare with those derived from species and communities; and how the selection and combination of variables influences the results. Collectively, they suggest 4 key steps when using geodiversity to augment traditional biodiversity-based conservation planning: create land units from species-relevant variables combined in an ecologically meaningful way; represent land units in a logical spatial configuration and integrate with species locations when possible; apply selection criteria to individual sites to ensure they are appropriate for conservation; and develop connectivity among sites to maintain movements and processes. With these considerations, conservationists can design more effective site portfolios to ensure the lasting conservation of biodiversity under a changing climate. © 2015 Society for Conservation Biology.
    No preview · Article · Apr 2015 · Conservation Biology
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    • "Several authors have noted (e.g. Fábrega-Álvarez and Parcero- Oubiña 2007, Gietl et al. 2008, Herzog 2010, Howey 2011, McRae et al. 2008, Neutens et al. 2010, Phillips et al. 2008, Zakšek et al. 2008) that the outputs of least-cost path models are more sensitive to used algorithms and input values than least-cost corridor analyses theoretically based on the time-geographical potential path area modelling. "
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    ABSTRACT: Published chapter available as a pdf on request (due to publisher's restrictions), here a final draft.
    Full-text · Chapter · May 2014
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