RANKING METAPOPULATION EXTINCTION RISK: FROM PATTERNS IN DATA TO CONSERVATION MANAGEMENT DECISIONS
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Abstract:
Viability analyses of large metapopulations are often hampered by difficulties in the parameter estimation. This leads to high uncertainty in parameter values and model outputs and complicates the formulation of clear recommendations for conservation management. We present a comprehensive procedure that is able to process spatiotemporal patterns of metapopulation occupancy to rank management scenarios. The first step of the procedure involves the formulation of the stochastic metapopulation model and the estimation of parameter values with a Bayesian approach, using a Markov chain Monte Carlo algorithm. In the second step, the model is used to predict the effects of different management actions, taking into account the uncertainty in the parameter estimates. Finally, in the third step, decision analysis is used to evaluate and aggregate the results of the previous step into a simple rank order of management scenarios. The procedure was applied to a metapopulation of the Glanville fritillary, Melitaea cinxia. Although the amount of available occupancy data was considerable, the uncertainty in the estimated model parameter values was so large that a precise estimate of the extinction risk of the metapopulation could not be made. However, the procedure was able to produce a rank order of management scenarios that was extraordinarily robust to the uncertainty. Application of the procedure to two other case studies revealed that, even though robust rankings cannot always be obtained, the results of the procedure are helpful in assessing the degree of uncertainty in the ranking and pointing to those factors most responsible for the lack of robustness. The results of this paper demonstrate very clearly, by way of example, both the limitations and the possibilities of model-based metapopulation viability analysis.Keywords:
Metapopulation
Occupancy
Robustness
Extinction (optical mineralogy)
Rank (graph theory)
Metapopulation theory assumes a balance between local decays/extinctions and local growth/new colonisations. Here we investigate whether recent population declines across part of the UK harbour seal range represent normal metapopulation dynamics or are indicative of perturbations potentially threatening the metapopulation viability, using 20 years of population trends, location tracking data (n = 380), and UK-wide, multi-generational population genetic data (n = 269). First, we use microsatellite data to show that two genetic groups previously identified are distinct metapopulations: northern and southern. Then, we characterize the northern metapopulation dynamics in two different periods, before and after the start of regional declines (pre-/peri-perturbation). We identify source-sink dynamics across the northern metapopulation, with two putative source populations apparently supporting three likely sink populations, and a recent metapopulation-wide disruption of migration coincident with the perturbation. The northern metapopulation appears to be in decay, highlighting that changes in local populations can lead to radical alterations in the overall metapopulation's persistence and dynamics.
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Abundance-occupancy relationships predict that species that occupy more sites are also more locally abundant, where occupancy is usually estimated following the assumption that species can occupy all sampled sites. Here we use the National Ecological Observatory Network small-mammal data to assess whether this assumption affects abundance-occupancy relationships. We estimated occupancy considering all sampled sites (traditional occupancy) and only the sites found within the species geographic range (spatial occupancy) and realized environmental niche (environmental occupancy). We found that when occupancy was estimated considering only sites possible for the species to colonize (spatial and environmental occupancy) weaker abundance-occupancy relationships were observed. This shows that the assumption that the species can occupy all sampled sites directly affects the assessment of abundance-occupancy relationships. Estimating occupancy considering only sites that are possible for the species to colonize will consequently lead to a more robust assessment of abundance-occupancy relationships.
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According to investigation on two species of melitaeine butterflies in Yanjiaping Village, Chicheng County, Hebei Province, China, between 1998-2002, together with the use of 1:10000 contour map of the local area, some conclusions are shown by the SPSS and GIS analysis of data obained from GPS: (1) The two species of melitaeine butterflies have different metapopulation structures. M. phoebe is a source-sink metapopulation, while E. aurinia is a classical metapopulation, supporting the analytic result from our former genetic research. (2) The two species of melitaeine butterflies exhibit different trends of population dynamics. M. phoebe source-sink metapopulation is very unsteady, and is always small, thus has a tendency to go extinct gradually. But E. aurinia classical metapopulation is stable, and has maintained a larger population size. Therefore, it stands a better chance of long-term survival. (3) The two species of melitaeine butterflies are significantly related in both patch occupancy and local population size. (4) The effect of isolation is significant on the metapopulations of these two species of melitaeine butterflies, consistent with the classical theories, whereas the effect of patch area is not significant on the metapopulations of these two species of melitaeine butterflies, which is inconsistent with the classical theories. Therefore, other factors, such as habitat quality, should be considered for their influences on metapopulations.
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A spatial correlated model for metapopulation has been constructed,which not only includes population information about spatial structutre,but also introduces the global density and local density of distructed habitat. Model reveals the spatial distribution pattern of destructed habitat profoundly effect the dynamics and persistence of metapopulation. The mixed distribution of two habitat types makes against metapopulation increase and persistence and mean-field assumption may overestimate the persistence of metapopulation in mixed habitat,but clustering distribution will promote its increase and persistence and mean-field assumption may underestimate the persistence of metapopulation in clustering habitat. Metapopulation persisitence is also affected by species migration. The longer migration distance,the more possibly species resists extinction from habitat destruction. All the resluts show that not only the number of destructed habitat is a main cause incuring metapopulation extinction but also the spatial distribution pattern of destruct landscape profoundly effect the dynamics and persistence of metapopulation. All these results show that it is important to costruct the connectivity among patches although habitat restoration and habitat quality improvement is necessary.
Metapopulation
Extinction (optical mineralogy)
Persistence (discontinuity)
Spatial heterogeneity
Local extinction
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A metapopulation model with explicit local dynamics is studied.Unlike many patch-based metapopulation models which assume thatthe local population within each patch is at its equilibrium,our model incorporates population changes in local patches that interact with metapopulation dynamics. The model keeps track of the fractions of patches that havespecies 1 only, species 2 only, or both species. For patcheswith both species, the Lotka-Volterra type of competition isassumed. It is shown that when the local dynamics is coupledwith the metapopulation dynamics the model outcomes can be verydifferent comparing with metapopulation models that do notexplicitly include local population dynamics. The analysis ofthe coupled system is carried out by using techniques in singularperturbation theory.
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Extinction (optical mineralogy)
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Patch dynamics
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