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Resilience of alternative states in spatially extended ecosystems.

van de Leemput IA, van Nes EH, Scheffer M - PLoS ONE (2015)

Bottom Line: We focus on the effect of local disturbances, defining resilience as the size of the area of a strong local disturbance needed to trigger a shift.Our results imply that local restoration efforts on a homogeneous landscape will typically either fail or trigger a landscape-wide transition.For extensive biomes with alternative stable states, such as tundra, steppe and forest, our results imply that, as climatic change reduces the stability, the effect might be difficult to detect until a point where local disturbances inevitably induce a spatial cascade to the alternative state.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Sciences, Wageningen University, Wageningen, The Netherlands.

ABSTRACT
Alternative stable states in ecology have been well studied in isolated, well-mixed systems. However, in reality, most ecosystems exist on spatially extended landscapes. Applying existing theory from dynamic systems, we explore how such a spatial setting should be expected to affect ecological resilience. We focus on the effect of local disturbances, defining resilience as the size of the area of a strong local disturbance needed to trigger a shift. We show that in contrast to well-mixed systems, resilience in a homogeneous spatial setting does not decrease gradually as a bifurcation point is approached. Instead, as an environmental driver changes, the present dominant state remains virtually 'indestructible', until at a critical point (the Maxwell point) its resilience drops sharply in the sense that even a very local disturbance can cause a domino effect leading eventually to a landscape-wide shift to the alternative state. Close to this Maxwell point the travelling wave moves very slow. Under these conditions both states have a comparable resilience, allowing long transient co-occurrence of alternative states side-by-side, and also permanent co-existence if there are mild spatial barriers. Overall however, hysteresis may mostly disappear in a spatial context as one of both alternative states will always tend to be dominant. Our results imply that local restoration efforts on a homogeneous landscape will typically either fail or trigger a landscape-wide transition. For extensive biomes with alternative stable states, such as tundra, steppe and forest, our results imply that, as climatic change reduces the stability, the effect might be difficult to detect until a point where local disturbances inevitably induce a spatial cascade to the alternative state.

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Example systems with alternative stable states in space.(a) Shallow lake: clear water with Chara vegetation vs. turbid water (photo by Ruurd Noordhuis). (b) Salt marsh: vegetation vs. bare marshland (photo by Johan van de Koppel). (c) Musselbed: mussels vs. bare soil (photo by Andre Meijboom).
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pone.0116859.g001: Example systems with alternative stable states in space.(a) Shallow lake: clear water with Chara vegetation vs. turbid water (photo by Ruurd Noordhuis). (b) Salt marsh: vegetation vs. bare marshland (photo by Johan van de Koppel). (c) Musselbed: mussels vs. bare soil (photo by Andre Meijboom).

Mentions: This question has been specifically addressed in the context of invasion dynamics of species with a strong local Allee effect [11–13]. These modeling studies show that alternative stable states may co-exist side-by-side provided that the landscape consists of discrete units. Discrete units can clearly be distinguished in certain ecosystems, such as coral reefs connected through larval exchange [14,15] or shallow ponds connected through overflows [16,17]. However, some systems have contrasting states co-existing in apparently continuous and homogeneous landscapes (e.g. Fig. 1). For example, within shallow lakes we can find sharp boundaries between clear water with submerged plants, and turbid water with no vegetation [18] (Fig. 1A). In marshlands, patches of vegetation can be found adjacent to non-vegetated mudflat [19] (Fig. 1B). Distinct boundaries are also found between mussel beds and bare soil in intertidal zones [20,21] (Fig. 1C). Other examples include boundaries between forest, savanna and grasslands [22,23], or between kelp beds and bare ocean floor covered by sea urchins [24,25].


Resilience of alternative states in spatially extended ecosystems.

van de Leemput IA, van Nes EH, Scheffer M - PLoS ONE (2015)

Example systems with alternative stable states in space.(a) Shallow lake: clear water with Chara vegetation vs. turbid water (photo by Ruurd Noordhuis). (b) Salt marsh: vegetation vs. bare marshland (photo by Johan van de Koppel). (c) Musselbed: mussels vs. bare soil (photo by Andre Meijboom).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4340810&req=5

pone.0116859.g001: Example systems with alternative stable states in space.(a) Shallow lake: clear water with Chara vegetation vs. turbid water (photo by Ruurd Noordhuis). (b) Salt marsh: vegetation vs. bare marshland (photo by Johan van de Koppel). (c) Musselbed: mussels vs. bare soil (photo by Andre Meijboom).
Mentions: This question has been specifically addressed in the context of invasion dynamics of species with a strong local Allee effect [11–13]. These modeling studies show that alternative stable states may co-exist side-by-side provided that the landscape consists of discrete units. Discrete units can clearly be distinguished in certain ecosystems, such as coral reefs connected through larval exchange [14,15] or shallow ponds connected through overflows [16,17]. However, some systems have contrasting states co-existing in apparently continuous and homogeneous landscapes (e.g. Fig. 1). For example, within shallow lakes we can find sharp boundaries between clear water with submerged plants, and turbid water with no vegetation [18] (Fig. 1A). In marshlands, patches of vegetation can be found adjacent to non-vegetated mudflat [19] (Fig. 1B). Distinct boundaries are also found between mussel beds and bare soil in intertidal zones [20,21] (Fig. 1C). Other examples include boundaries between forest, savanna and grasslands [22,23], or between kelp beds and bare ocean floor covered by sea urchins [24,25].

Bottom Line: We focus on the effect of local disturbances, defining resilience as the size of the area of a strong local disturbance needed to trigger a shift.Our results imply that local restoration efforts on a homogeneous landscape will typically either fail or trigger a landscape-wide transition.For extensive biomes with alternative stable states, such as tundra, steppe and forest, our results imply that, as climatic change reduces the stability, the effect might be difficult to detect until a point where local disturbances inevitably induce a spatial cascade to the alternative state.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Sciences, Wageningen University, Wageningen, The Netherlands.

ABSTRACT
Alternative stable states in ecology have been well studied in isolated, well-mixed systems. However, in reality, most ecosystems exist on spatially extended landscapes. Applying existing theory from dynamic systems, we explore how such a spatial setting should be expected to affect ecological resilience. We focus on the effect of local disturbances, defining resilience as the size of the area of a strong local disturbance needed to trigger a shift. We show that in contrast to well-mixed systems, resilience in a homogeneous spatial setting does not decrease gradually as a bifurcation point is approached. Instead, as an environmental driver changes, the present dominant state remains virtually 'indestructible', until at a critical point (the Maxwell point) its resilience drops sharply in the sense that even a very local disturbance can cause a domino effect leading eventually to a landscape-wide shift to the alternative state. Close to this Maxwell point the travelling wave moves very slow. Under these conditions both states have a comparable resilience, allowing long transient co-occurrence of alternative states side-by-side, and also permanent co-existence if there are mild spatial barriers. Overall however, hysteresis may mostly disappear in a spatial context as one of both alternative states will always tend to be dominant. Our results imply that local restoration efforts on a homogeneous landscape will typically either fail or trigger a landscape-wide transition. For extensive biomes with alternative stable states, such as tundra, steppe and forest, our results imply that, as climatic change reduces the stability, the effect might be difficult to detect until a point where local disturbances inevitably induce a spatial cascade to the alternative state.

Show MeSH
Related in: MedlinePlus