Habitat‐specific demography, source‐sink dynamics, and the niche of a common shrub in a heterogeneous and fluctuating environment

Abstract

The occurrence of a species in habitats of varying quality connected through migration can only be understood by detailed investigation of itsdemography. In the Chihuahuan Desert, the common shrub Flourensia cernua is found in both productive and unproductive areas. In the former, both growing and senescent populations are regularly found, while in the latter a low density scattered population persists indefinitely. While precipitation (and its annual stochastic variation) is the same in both habitats, their geomorphological differences produce a sharp difference in the availability of the limiting resource, water. This produces different population dynamics in F. cernua, but also radically different plant communities. Counterintuitively, the low‐resource habitat (LR) supports a scattered, slightly increasing or stable population that coexists with its neighbors and acts as exporter of seeds (source population). In contrast, the high‐resource habitat (HR) allows sporadic recruitment of locally dense patches that tend towards extinction (sink population). The latter is accounted for by the increasing dominance of the grass Pleuraphys mutica. The different dynamics and regulatory mechanisms in each habitat allow the species to occupy a wider distribution than it would have in their absence. The higher abundance of F. cernua in the sink habitat, together with its consequences on community composition and dynamics, questions the idea proposed in the literature that a sink population lives outside its fundamental niche. The study provides support to the notion that the ecological niche of a species cannot be completely characterized by its requirements (e.g. as they relate to physiology), but must also include the complex demographic responses to a spatially and temporally variable environment, which may often include substandard conditions. For the niche concept to retain its usefulness, it must incorporate the demographic response of populations to spatially and temporallyvariable resource supply.

Coexistence and the niche in a nurse–cactus interaction: Is cyclic dynamics justified?

“…being limited by the same limiting resource) all the time. We documented a similar effect in a study of one species, Flourensia cernua , in two contiguous and contrasting habitats in the same study zone that represented, respectively, a source and a sink population (Ferrer et al, ). In each habitat, F. cernua was limited by the same resource, water, but the respective populations had contrasting demographics.…”

“…As in other shrubs of arid zones: (Ferrer et al, ; Golubov et al, ; Jiménez‐Lobato & Valverde, ; Miriti et al, ; Silvertown, Franco, & Menges, ; Verhulst et al, ), the elasticity of survival (σ) dominated in all four subpopulations. Larrea was able to compensate for the decrease in the contribution of growth (γ) and fecundity (φ) to population growth rate, when in association with Cylindropuntia , by increasing the contribution of survival (σ).…”

“…After the first observations that the recruitment of many species in arid environments was favoured by a shaded microenvironment located under the canopy of shrubs (Niering, Whittaker, & Lowe, 1963;Shreve, 1931), many studies have confirmed the relevance of facilitation (Flores & Jurado, 2003), and its prevalence has been confirmed at different ecological scales (see reviews by Brooker et al, 2007;Callaway, 2007). On the other hand, the importance of competition in structuring vegetation in arid environments has generated a substantial amount of work suggesting that in these unproductive environments, plants compete intensely for the most limiting resource, water (see reviews by Fowler, 1986;Goldberg & Barton, 1992), yet have evolved morphological, physiological and demographic mechanisms that allow them to coexist (Cázares-Martínez, Montaña, & Franco, 2010;Ferrer, Montaña, & Franco, 2015;Goldberg & Novoplansky, 1997;Nobel, 1997;Schwinning & Ehleringer, 2001;Silvertown, 2004;Verhulst, Montaña, Mandujano, & Franco, 2008).…”

Population dynamics of desert mammals: similarities and contrasts within a multispecies assemblage

“…, Ferrer et al. ). Sub‐populations near ephemeral waters thus may exhibit increased survival or greater densities of animals than those in more xeric sites (Kok and Nel ), in turn setting the local dynamics at these sites on different trajectories (Céré et al.…”

Regional distribution patterns can predict the local habitat specialization of arachnids in heterogeneous landscapes of the Atlantic Forest

“…Studies suggest that species highly specialized in forested biomes are hardly able to use non‐forested areas of their biome or newly created open habitats (Cantalapiedra, Fernández, & Morales, ; Halffter, ; Vrba, ). However, we do not predict total agreement between the empirical classification and model 3 classification at landscape scale because ecological interactions can move the species from their preferred habitat (Bolnick et al., ), and individuals that are not able to complete their life cycle can be found in landscape portions, simply because they are scattered from the preferred habitat due to ecological interactions or searching for resources (Amarasekare & Nisbet, ; Ferrer, Montaña, & Franco, ). Therefore, a species predicted to be a forest specialist based on its occurrence in only forested habitats may be forced to use forest edges or open habitats to survive.…”