Biomedical subjects

Johan van de Koppel

Publications and source records attributed to Johan van de Koppel.

7 recordsLinked to original sources

PubMed2006

Scale-dependent inhibition drives regular tussock spacing in a freshwater marsh.

Regular spatial patterning is common in nature, and various mechanisms of self-organization have been proposed to explain regular patterning. We report on regular spatial patterning in Carex stricta in a freshwater wetland and investigate the applicability of theoretical models that explain regular patterning based on inhibition, facilitation, or interaction between the two. Spectral analysis of aerial photographs revealed that tussocks were regularly spaced at an average distance of 60 cm. Photosynthetically active radiation varied significantly with distance from the tussock and was lowest at intermediate distance from the tussock center (15-40 cm). Using transplants to assay growth conditions, we found that C. stricta grew well in all distance classes with and without natural C. stricta biomass, except at intermediate distances when buried in C. stricta wrack. Our experimental results reveal that C. stricta inhibits its growth in a scale-dependent manner: inhibition was found to peak at intermediate distance from the tussock. We compared three alternative models to examine potential mechanisms driving regularity and found that, similar to our experimental results, scale-dependent inhibition provides the best explanation for the observed regular tussock spacing. Our study underlines the importance of scale-dependent feedback in the formation of regular spatial patterning in ecosystems.

Carex Plant↗

PubMed2006

Scale-dependent interactions and community structure on cobble beaches.

Recent theory suggests that scale-dependent interaction between facilitation and competition can generate spatial structure in ecological communities. The application of this hypothesis, however, has been limited to systems with little underlying heterogeneity. We evaluated this prediction in a plant community along an intertidal stress gradient on cobble beaches in Rhode Island, USA. Prior studies have shown that Spartina alterniflora facilitates a forb-dominated community higher in the intertidal by modifying the shoreline environment. We tested the hypothesis that, at a smaller scale, Spartina competitively excludes forb species, explaining their marked absence within the lower Spartina zone. Transplant experiments showed forb species grow significantly better in the Spartina zone when neighbours were removed. Removal of the Spartina canopy led to a massive emergence of annual forbs, showing that competition limits local occupation. These findings indicate that interaction of large-scale facilitation and small-scale competition drives plant zonation on cobble beaches. This study is the first to provide empirical evidence of scale-dependent interactions between facilitation and competition spatially structuring communities in heterogeneous environments.

Chenopodiaceae↗

PubMed2005

Drought, snails, and large-scale die-off of southern U.S. salt marshes.

Salt marshes in the southeastern United States have recently experienced massive die-off, one of many examples of widespread degradation in marine and coastal ecosystems. Although intense drought is thought to be the primary cause of this die-off, we found snail grazing to be a major contributing factor. Survey of marsh die-off areas in three states revealed high-density fronts of snails on die-off edges at 11 of 12 sites. Exclusion experiments demonstrated that snails actively converted marshes to exposed mudflats. Salt addition and comparative field studies suggest that drought-induced stress and grazers acted synergistically and to varying degrees to cause initial plant death. After these disturbances, snail fronts formed on die-off edges and subsequently propagated through healthy marsh, leading to cascading vegetation loss. These results, combined with model analyses, reveal strong interactions between increasing climatic stress and grazer pressure, both potentially related to human environmental impacts, which amplify the likelihood and intensity of runaway collapse in these coastal systems.

Animals↗

PubMed2005

Scale-dependent feedback and regular spatial patterns in young mussel beds.

In the past decade, theoretical ecologists have emphasized that local interactions between predators and prey may invoke emergent spatial patterning at larger spatial scales. However, empirical evidence for the occurrence of emergent spatial patterning is scarce, which questions the relevance of the proposed mechanisms to ecological theory. We report on regular spatial patterns in young mussel beds on soft sediments in the Wadden Sea. We propose that scale-dependent feedback, resulting from short-range facilitation by mutual protection from waves and currents and long-range competition for algae, induces spatial self-organization, thereby providing a possible explanation for the observed patterning. The emergent self-organization affects the functioning of mussel bed ecosystems by enhancing productivity and resilience against disturbance. Moreover, self-organization allows mussels to persist at algal concentrations that would not permit survival of mussels in a homogeneous bed. Our results emphasize the importance of self-organization in affecting the emergent properties of natural systems at larger spatial scales.

Animals↗

PubMed2004

Self-organization and vegetation collapse in salt marsh ecosystems.

Complexity theory predicts that local feedback processes may strongly affect the organization of ecosystems on larger spatial scales. Whether complexity leads to increased resilience and stability or to increased vulnerability and criticality remains one of the dominant questions in ecology. We present a combined theoretical and empirical study of complex dynamics in mineralogenic salt marsh ecosystems that emerge from a positive feedback between clay accumulation and plant growth. Positive feedback induces self-organizing within the ecosystem, which buffers for the strong physical gradient that characterizes the marine-terrestrial boundary, and improves plant growth along the gradient. However, as a consequence of these self-organizing properties, salt marshes approach a critical state as the edge of the salt marsh and the adjacent intertidal flat becomes increasingly steep and vulnerable to wave attack. Disturbance caused, for instance, by a storm may induce a cascade of vegetation collapse and severe erosion on the cliff edge, leading to salt marsh destruction. Our study shows that on short timescales, self-organization improves the functioning of salt marsh ecosystems. On long timescales, however, self-organization may lead to destruction of salt marsh vegetation.

Biodiversity↗

PubMed2004

Self-organized patchiness and catastrophic shifts in ecosystems.

Unexpected sudden catastrophic shifts may occur in ecosystems, with concomitant losses or gains of ecological and economic resources. Such shifts have been theoretically attributed to positive feedback and bistability of ecosystem states. However, verifications and predictive power with respect to catastrophic responses to a changing environment are lacking for spatially extensive ecosystems. This situation impedes management and recovery strategies for such ecosystems. Here, we review recent studies on various ecosystems that link self-organized patchiness to catastrophic shifts between ecosystem states.

Ecosystem↗

PubMed2004

Spatial interactions and resilience in arid ecosystems.

We present a mathematical analysis of the consequences of spatial interactions between vegetation patches by means of water flow for the functioning of arid systems. Our model results suggest that spatial exchange of water improved the resilience to disturbances and increased the resistance to human-induced loss of cover. Furthermore, spatial exchange of water allowed vegetation to persist at lower rainfall levels compared to systems that lack spatial interactions. Our analysis stresses the general importance of spatial interactions for the functioning of ecological systems.

Climate↗