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AARHUS UNIVERSITY
NATIONAL ENVIRONMENTAL RESEARCH INSTITUTE
Beetle Vole Skylark Spider
A B C D
2
3
4
9
10
11
12
13
14
φ
A B C D
0
1
2
3
4
9
10
11
12
13
A B C D
1
2
3
8
9
A B C D
0
1
2
11
12
Log
e (K
)
UnperturbedPerturbed 80 pct.Perturbed 95 pct.
Beetle Vole Skylark Spider
Log
e (N
)
Years since perturbation
8
9
10
11
12
13
0 5 10 15
5
6
7
8
9
10
11
6
7
8
9
10
8
9
10
11
12
0 5 10 15 0 5 10 15 0 5 10 15
Times perturbed
12345
678910
Main roadRoadside vergeHedgePermanent grassUnmanaged grasslandRotational field (all crops)Coniferous forestDeciduous forest
Fig 1. Model landscapes.
Jacob Nabe-Nielsen1,2, Richard M. Sibly2,3, Mads C. Forchhammer1,2, Valery E. Forbes2,4
IntroductionThe arrangement of patches in a landscape and the degree to which they are connected by corridors are thought to be important for the long-term conservation of many species, and may determine whether they are able to recover from large-scale disturbances [1,2].
In fragmented landscapes subpopulations are isolated and less likely to be maintained through continuous immigra-tion. Recolonization of empty habitat patches may also take longer, resulting in lower population sizes on the landscape scale, especially for short-dispersing species.
MethodsHere we use individual-based population models (IBMs) to evaluate to what extent animal population recovery after disturbances is affected by land-scape structure. In our models fluctuations in population sizes emerge as a result of realistic site-specific behavior of individual animals and their inter-actions with each other.
We simulated population dynamics in four 10×10 km landscapes (Fig. 1): (A) real landscape; (B) landscape without corridors; (C) landscape with randomized patch arrangement; (D) landscape with randomized patch sizes. Fragmentation increased in A–C [3].
We selected four species with contrasting life-histories in order to study if population recovery was related to dispersal. Recovery to equilibrium popu-lation size (K) after a perturbation was measured using the return time (φ), which was calculated from the shape of the logistic curve fitted to popula-tion size vs. number of years since perturbation (Fig. 2).
Results and conclusionsThe short-dispersing species (beetle and vole) recovered slowly from perturbations in landscapes where they had low K (Fig. 3). Beetles had high K in landscapes where over-wintering habitats (field boundaries) were located close to summer habitats (fields). Voles had high K when their key habitat (unmanaged grass) was abundant, especially if the edge lengths in these habitats were relatively short.
Skylark had low K in landscapes with randomized patch arrangement (C). Here forest patches are dispersed throughout the landscape, and skylarks avoid nesting close to trees.
This study underlines the need to study population dynamics in a spatial context, and to explicitly include all relevant habitat types. This is most easily done with mechanistically rich IBMs.
References1 Nabe-Nielsen, J., Sibly, R.M., Forchhammer, M.C., Forbes, V.E., Topping, C.J., 2010. PLoS ONE 5, e8932.2 Vos, C.C., Verboom, J., Opdam, P.F.M., Ter Braak, C.J.F., 2001. Am. Nat. 157, 24-41. 3 Fahrig, L., 2003. Ann. Rev. Ecol. Evol. Syst. 34, 487-515.
Fig. 2. Population recovery after removing 95% of the individuals (real landscape). Population numbers (N) were counted yearly for 170 years. Perturbations took place every 17 years.
Fig. 3. Equilibrium population sizes (K) and return times (φ) in landscapes of decreasing complexity (letters on x-axes correspond to Fig. 1). Error bars are 95% confidence intervals.
Background paper: doi:10.1371/journal.pone.0008932
Contact: [email protected]
1 NERI, Aarhus University, 2 CIPE, 3 University of Reading, 4 Roskilde University
