History-dependent patterns of whole ecosystems

Sherratt, Jonathan A.

doi:10.1016/j.ecocom.2012.12.002

Cited by 61 publications

(71 citation statements)

References 61 publications

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“…Under these homogeneous conditions, self-organized systems can exhibit multiple stable states, as was predicted for arid environments [16,18]. Gradients are caused by externally imposed spatial variation, such as elevational variation in mountain areas affecting vegetation zonation [19].…”

Section: Introductionmentioning

confidence: 95%

Biogenic gradients in algal density affect the emergent properties of spatially self-organized mussel beds

Liu

Weerman

Gupta

et al. 2014

J. R. Soc. Interface.

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Theoretical models highlight that spatially self-organized patterns can have important emergent effects on the functioning of ecosystems, for instance by increasing productivity and affecting the vulnerability to catastrophic shifts. However, most theoretical studies presume idealized homogeneous conditions, which are rarely met in real ecosystems. Using self-organized mussel beds as a case study, we reveal that spatial heterogeneity, resulting from the large-scale effects of mussel beds on their environment, significantly alters the emergent properties predicted by idealized self-organization models that assume homogeneous conditions. The proposed model explicitly considers that the suspended algae, the prime food for the mussels, are supplied by water flow from the seaward boundary of the bed, which causes in combination with consumption a gradual depletion of algae over the simulated domain. Predictions of the model are consistent with properties of natural mussel patterns observed in the field, featuring a decline in mussel biomass and a change in patterning. Model analyses reveal a fundamental change in ecosystem functioning when this self-induced algal depletion gradient is included in the model. First, no enhancement of secondary productivity of the mussels comparing with non-patterns states is predicted, irrespective of parameter setting; the equilibrium amount of mussels is entirely set by the input of algae. Second, alternate stable states, potentially present in the original (no algal gradient) model, are absent when gradual depletion of algae in the overflowing water layer is allowed. Our findings stress the importance of including sufficiently realistic environmental conditions when assessing the emergent properties of self-organized ecosystems.

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Section: Introductionmentioning

confidence: 95%

Biogenic gradients in algal density affect the emergent properties of spatially self-organized mussel beds

Liu

Weerman

Gupta

et al. 2014

J. R. Soc. Interface.

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“…When rainfall slowly increases, this will be the wavelength of the first patterns to be established, which will then persist following further moderate changes in rainfall (19,23,38). My procedure was to solve [1] numerically with A = A c and with u set to u s in the center of the domain (in a region of width arbitrarily chosen to be 200), and zero otherwise.…”

Section: Methodsmentioning

confidence: 99%

“…Eq. 1 is one of the earliest and simplest models for vegetation patterning, and remains in widespread use (19)(20)(21)(22)(23). Crucially, there are only four dimensionless parameters, which makes comprehensive scans of parameter space feasible.…”

Section: Mathematical Modeling Of Semiarid Vegetationmentioning

confidence: 99%

“…Nevertheless prediction of pattern wavelength is possible. Studies of both [1] and other models for semiarid vegetation have shown that as environmental parameters are gradually changed, the wavelength of banded vegetation patterns remains constant (19,23,37,38) (Fig. 2).…”

Section: Pattern Generation From Uniform Vegetationmentioning

confidence: 99%

“…Models then predict that the pattern breaks down and reforms with a longer (shorter) wavelength (Fig. 2); the occurrence of such transitions can be predicted via the patterns crossing the "stability boundary" (19,23,38) (Fig. 2).…”

Section: Pattern Generation From Uniform Vegetationmentioning

confidence: 99%

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Using wavelength and slope to infer the historical origin of semiarid vegetation bands

Sherratt

2015

Proc. Natl. Acad. Sci. U.S.A.

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Landscape-scale patterns of vegetation occur worldwide at interfaces between semiarid and arid climates. They are important as potential indicators of climate change and imminent regime shifts and are widely thought to arise from positive feedback between vegetation and infiltration of rainwater. On gentle slopes the typical pattern form is bands (stripes), oriented parallel to the contours, and their wavelength is probably the most accessible statistic for vegetation patterns. Recent field studies have found an inverse correlation between pattern wavelength and slope, in apparent contradiction with the predictions of mathematical models. Here I show that this “contradiction” is based on a flawed approach to calculating the wavelength in models. When pattern generation is considered in detail, the theory is fully consistent with empirical results. For realistic parameters, degradation of uniform vegetation generates patterns whose wavelength increases with slope, whereas colonization of bare ground gives the opposite trend. Therefore, the empirical finding of an inverse relationship can be used, in conjunction with climate records, to infer the historical origin of the patterns. Specifically, for the African Sahel my results suggest that banded vegetation originated by the colonization of bare ground during circa 1760–1790 or since circa 1850.

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How will increases in rainfall intensity affect semiarid ecosystems?

Siteur

Eppinga

Karssenberg

et al. 2014

Water Resources Research

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Model studies suggest that semiarid ecosystems with patterned vegetation can respond in a nonlinear way to climate change. This means that gradual changes can result in a rapid transition to a desertified state. Previous model studies focused on the response of patterned semiarid ecosystems to changes in mean annual rainfall. The intensity of rain events, however, is projected to change as well in the coming decades. In this paper, we study the effect of changes in rainfall intensity on the functioning of patterned semiarid ecosystems with a spatially explicit model that captures rainwater partitioning and runoff-runon processes with simple event-based process descriptions. Analytical and numerical analyses of the model revealed that rainfall intensity is a key parameter in explaining patterning of vegetation in semiarid ecosystems as low mean rainfall intensities do not allow for vegetation patterning to occur. Surprisingly, we found that, for a constant annual rainfall rate, both an increase and a decrease in mean rainfall intensity can trigger desertification. An increase negatively affects productivity as a greater fraction of the rainwater is lost as runoff. This can result in a shift to a bare desert state only if the mean rainfall intensity exceeds the infiltration capacity of bare soil. On the other hand, a decrease in mean rainfall intensity leads to an increased fraction of rainwater infiltrating in bare soils, remaining unavailable to plants. Our findings suggest that considering rainfall intensity as a variable may help in assessing the proximity to regime shifts in patterned semiarid ecosystems and that monitoring losses of resource through runoff and bare soil infiltration could be used to determine ecosystem resilience.

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History-dependent patterns of whole ecosystems

Cited by 61 publications

References 61 publications

Biogenic gradients in algal density affect the emergent properties of spatially self-organized mussel beds

Biogenic gradients in algal density affect the emergent properties of spatially self-organized mussel beds

Using wavelength and slope to infer the historical origin of semiarid vegetation bands

How will increases in rainfall intensity affect semiarid ecosystems?

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