Ecosystem Engineers: From Pattern Formation to Habitat Creation

Abstract

Habitat and species richness in drylands are affected by the dynamics of a few key species, termed "ecosystem engineers." These species modulate the landscape and redistribute the water resources so as to allow the introduction of other species. A mathematical model is developed for a pair of ecosystem engineers commonly found in drylands: plants forming vegetation patterns and cyanobacteria forming soil crusts. The model highlights conditions for habitat creation and for high habitat richness, and suggests a novel mechanism for species loss events as a result of environmental changes.

Local properties of patterned vegetation: quantifying endogenous and exogenous effects

“…Three scenarios illustrating potential mechanisms are shown in figure 7 and could form the basis for future field studies. First, shallow soils could promote lateral root extension by plants, exaggerating the effects of root competition [25,26] (figure 7a,b). Studies of Chihuahuan desert species confirm that there is intense root competition in the zone above the petrocalcic horizon, where root growth is concentrated [72].…”

“…All of these morphologies can be related to the presence, strength and directionality of positive feedbacks that concentrate resources (such as nutrients, soil carbon and water) that sustain plant life in a localized region near the plants [19][20][21][22][23][24]. These feedbacks have led to the moniker 'ecosystem engineers' being applied to perennial plants in dryland ecosystems: they create the conditions necessary for their own survival [25,26].…”

Periodic versus scale-free patterns in dryland vegetation

“…Here, X ¼ ðX; Y Þ are the spatial coordinates, T is time and r 2 ¼ @ X 2 þ @ Y 2 is the Laplacian operator. We refer the reader to Gilad et al (2004Gilad et al ( , 2007a for a detailed presentation of the model. Here, we focus on the quantities and terms that are most relevant to the present study.…”

“…These include vegetation patterns and pattern transitions along environmental-stress gradients (rainfall, grazing; Gilad et al 2004Gilad et al , 2007a, productivity-resilience trade-offs in banded vegetation on hill slopes (Yizhaq et al 2005), mechanisms of vegetation-ring formation (Sheffer et al 2007), plants as ecosystem engineers (Gilad et al 2004Meron et al 2007a,b), transition from competition to facilitation in woody-herbaceous systems along rainfall gradients , mechanisms of species coexistence associated with spatial patterning , and effects of stochastic rainfall on vegetation production and land coverage (Kletter et al 2009). …”

“…Surprisingly, despite the vast literature on vegetation patchiness and the longstanding dichotomy of periodic versus scale-free patterns, studies along this direction have hardly been pursued (Manor & Shnerb 2008b). In this paper, we use the model that has been introduced by Gilad et al (2004Gilad et al ( , 2007a to unravel eco-physical conditions that give rise to scale-free vegetation patterns and to study transitions from scalefree patterns to periodic patterns when these conditions are not satisfied.…”