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Combining incidence and demographic modelling approaches to evaluate metapopulation parameters for an endangered riparian plant

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ABSTRACT

Metapopulations are a central concept in ecology and conservation biology; however, estimating key parameters such as colonization rates presents a substantial obstacle to modelling metapopulations in many species. We develop spatial and non-spatial simulation models that combine incidence- and demographic-based approaches to build a relationship between observed patch occupancy, habitat turnover rates, colonization rates and dispersal scales. Applying these models to long-term observations of Pedicularis furbishiae (Furbish’s lousewort), a rare plant endemic to the Saint John River, we predict that observed habitat patches averaging 550 m in length receive colonizing seedlings with a yearly probability of 0.45 or 0.54, based on two different models. Predictions are consistent with a standard analytic metapopulation formulation modified to partition extinction drivers during the early and the late phases of a population’s life cycle. While the specific results rest on several simplifying assumptions, the models allow us to understand the impact that increasing rates of habitat turnover would have on the future survival of this species.

No MeSH data available.


Simulated occupancy in a spatial model of Pedicularis furbishiae at 149 patches estimated from 20 iterations at each parameterization of characteristic scale and dispersal ratio. Patch occupancy is defined as the number of patches with at least one reproductive adult. The characteristic scale defines the exponential distribution used for seedling dispersal. The dispersal ratio specifies the ratio of additional dispersing seedlings relative to the number of seedlings recruited within each patch.
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plw044-F3: Simulated occupancy in a spatial model of Pedicularis furbishiae at 149 patches estimated from 20 iterations at each parameterization of characteristic scale and dispersal ratio. Patch occupancy is defined as the number of patches with at least one reproductive adult. The characteristic scale defines the exponential distribution used for seedling dispersal. The dispersal ratio specifies the ratio of additional dispersing seedlings relative to the number of seedlings recruited within each patch.

Mentions: In the spatial model, the occupancy at the end of simulation runs was affected by both the characteristic scale and the number of dispersing seedlings. Within this parameter space, the ending occupancy matched our observed occupancy, 0.77, for simulations along a curved path (Fig. 3). When the dispersal scale was between 1 and 100 km, simulated occupancy matched the observed occupancy when the dispersal ratio was between 0.007 and 0.4. When the dispersal ratio was >1, the characteristic scale needed to be between 30 and 200 m for the simulation occupancy to match the observed occupancy. In 134 simulations for which simulated and observed occupancy matched, the mean annual probability of a patch receiving one or more dispersing seedlings was 0.54 (SD = 0.11; Fig. 4). Colonization was bi-modally distributed, with many patches receiving no dispersing seedlings and many patches receiving dispersing seedlings every year. In the 134 simulations matching observed occupancy, the mean annual probability of an unoccupied patch received dispersing individuals was 0.51 (SD = 0.11), whereas in occupied patches, this probability was 0.6 (SD = 0.13). Increasing the cost factor for dispersing across the river (b) caused ∼6.5 % lower occupancy rates [see Supporting Information – Fig. 5]. Compared with simulations with no downstream bias in seed dispersal, when f = 0.5, occupancy rates were 7–9 % lower when f  0.99, and 13–14 % higher when f 0.01.Figure 3.


Combining incidence and demographic modelling approaches to evaluate metapopulation parameters for an endangered riparian plant
Simulated occupancy in a spatial model of Pedicularis furbishiae at 149 patches estimated from 20 iterations at each parameterization of characteristic scale and dispersal ratio. Patch occupancy is defined as the number of patches with at least one reproductive adult. The characteristic scale defines the exponential distribution used for seedling dispersal. The dispersal ratio specifies the ratio of additional dispersing seedlings relative to the number of seedlings recruited within each patch.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940506&req=5

plw044-F3: Simulated occupancy in a spatial model of Pedicularis furbishiae at 149 patches estimated from 20 iterations at each parameterization of characteristic scale and dispersal ratio. Patch occupancy is defined as the number of patches with at least one reproductive adult. The characteristic scale defines the exponential distribution used for seedling dispersal. The dispersal ratio specifies the ratio of additional dispersing seedlings relative to the number of seedlings recruited within each patch.
Mentions: In the spatial model, the occupancy at the end of simulation runs was affected by both the characteristic scale and the number of dispersing seedlings. Within this parameter space, the ending occupancy matched our observed occupancy, 0.77, for simulations along a curved path (Fig. 3). When the dispersal scale was between 1 and 100 km, simulated occupancy matched the observed occupancy when the dispersal ratio was between 0.007 and 0.4. When the dispersal ratio was >1, the characteristic scale needed to be between 30 and 200 m for the simulation occupancy to match the observed occupancy. In 134 simulations for which simulated and observed occupancy matched, the mean annual probability of a patch receiving one or more dispersing seedlings was 0.54 (SD = 0.11; Fig. 4). Colonization was bi-modally distributed, with many patches receiving no dispersing seedlings and many patches receiving dispersing seedlings every year. In the 134 simulations matching observed occupancy, the mean annual probability of an unoccupied patch received dispersing individuals was 0.51 (SD = 0.11), whereas in occupied patches, this probability was 0.6 (SD = 0.13). Increasing the cost factor for dispersing across the river (b) caused ∼6.5 % lower occupancy rates [see Supporting Information – Fig. 5]. Compared with simulations with no downstream bias in seed dispersal, when f = 0.5, occupancy rates were 7–9 % lower when f  0.99, and 13–14 % higher when f 0.01.Figure 3.

View Article: PubMed Central - PubMed

ABSTRACT

Metapopulations are a central concept in ecology and conservation biology; however, estimating key parameters such as colonization rates presents a substantial obstacle to modelling metapopulations in many species. We develop spatial and non-spatial simulation models that combine incidence- and demographic-based approaches to build a relationship between observed patch occupancy, habitat turnover rates, colonization rates and dispersal scales. Applying these models to long-term observations of Pedicularis furbishiae (Furbish’s lousewort), a rare plant endemic to the Saint John River, we predict that observed habitat patches averaging 550 m in length receive colonizing seedlings with a yearly probability of 0.45 or 0.54, based on two different models. Predictions are consistent with a standard analytic metapopulation formulation modified to partition extinction drivers during the early and the late phases of a population’s life cycle. While the specific results rest on several simplifying assumptions, the models allow us to understand the impact that increasing rates of habitat turnover would have on the future survival of this species.

No MeSH data available.