Limits...
Spatial complementarity and the coexistence of species.

Velázquez J, Garrahan JP, Eichhorn MP - PLoS ONE (2014)

Bottom Line: Alternatively, individuals of the same species might compete over greater distances, known as heteromyopia, breaking down clusters and opening space for a second species to invade.This results in a common framework for predicting, given any pair of species and knowledge of the relevant parameters, whether they will coexist, the mechanism by which they will do so, and the resultant spatial pattern of the community.Spatial coexistence arises from complementary combinations of traits in each species rather than solely through self-limitation.

View Article: PubMed Central - PubMed

Affiliation: School of Physics & Astronomy, The University of Nottingham, University Park, Nottingham, NG7 2RD, United Kingdom; Facultad de Ciencias Físico Matemáticas, Universidad Autónoma de Puebla, 72001, Puebla, Pue., México.

ABSTRACT
Coexistence of apparently similar species remains an enduring paradox in ecology. Spatial structure has been predicted to enable coexistence even when population-level models predict competitive exclusion if it causes each species to limit its own population more than that of its competitor. Nevertheless, existing hypotheses conflict with regard to whether clustering favours or precludes coexistence. The spatial segregation hypothesis predicts that in clustered populations the frequency of intra-specific interactions will be increased, causing each species to be self-limiting. Alternatively, individuals of the same species might compete over greater distances, known as heteromyopia, breaking down clusters and opening space for a second species to invade. In this study we create an individual-based model in homogeneous two-dimensional space for two putative sessile species differing only in their demographic rates and the range and strength of their competitive interactions. We fully characterise the parameter space within which coexistence occurs beyond population-level predictions, thereby revealing a region of coexistence generated by a previously-unrecognised process which we term the triadic mechanism. Here coexistence occurs due to the ability of a second generation of offspring of the rarer species to escape competition from their ancestors. We diagnose the conditions under which each of three spatial coexistence mechanisms operates and their characteristic spatial signatures. Deriving insights from a novel metric - ecological pressure - we demonstrate that coexistence is not solely determined by features of the numerically-dominant species. This results in a common framework for predicting, given any pair of species and knowledge of the relevant parameters, whether they will coexist, the mechanism by which they will do so, and the resultant spatial pattern of the community. Spatial coexistence arises from complementary combinations of traits in each species rather than solely through self-limitation.

Show MeSH
Typical density  of two species obtained from linear transects through the coexistence diagram in Fig. 2c for the simulated communities.Blue line and circles: species 1; red line and squares: species 2. a) for variation in  with , b) for variation in  with . All other parameters as Fig. 1.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4274010&req=5

pone-0114979-g003: Typical density of two species obtained from linear transects through the coexistence diagram in Fig. 2c for the simulated communities.Blue line and circles: species 1; red line and squares: species 2. a) for variation in with , b) for variation in with . All other parameters as Fig. 1.

Mentions: The transition from coexistence to competitive exclusion in the simulations occurs due to continuous changes in the densities () of each species, rather than a sharp boundary (Fig. 3). Fig. 3a demonstrates that there is an important region of parameter space in which despite species 2 being competitively weaker () it is numerically dominant (i.e. the red line is above the blue). From Fig. 3b we can see that the susceptibility of a species' population density to changes in its intrinsic death rate is greater (i.e. a steeper slope) when another species is present, even as a minority element. These patterns reinforce our view that complementarity is central to understanding coexistence, since the density of each species responds to the presence of the other; it is not merely the case that an inferior competitor fits around the pattern generated by the stronger species.


Spatial complementarity and the coexistence of species.

Velázquez J, Garrahan JP, Eichhorn MP - PLoS ONE (2014)

Typical density  of two species obtained from linear transects through the coexistence diagram in Fig. 2c for the simulated communities.Blue line and circles: species 1; red line and squares: species 2. a) for variation in  with , b) for variation in  with . All other parameters as Fig. 1.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4274010&req=5

pone-0114979-g003: Typical density of two species obtained from linear transects through the coexistence diagram in Fig. 2c for the simulated communities.Blue line and circles: species 1; red line and squares: species 2. a) for variation in with , b) for variation in with . All other parameters as Fig. 1.
Mentions: The transition from coexistence to competitive exclusion in the simulations occurs due to continuous changes in the densities () of each species, rather than a sharp boundary (Fig. 3). Fig. 3a demonstrates that there is an important region of parameter space in which despite species 2 being competitively weaker () it is numerically dominant (i.e. the red line is above the blue). From Fig. 3b we can see that the susceptibility of a species' population density to changes in its intrinsic death rate is greater (i.e. a steeper slope) when another species is present, even as a minority element. These patterns reinforce our view that complementarity is central to understanding coexistence, since the density of each species responds to the presence of the other; it is not merely the case that an inferior competitor fits around the pattern generated by the stronger species.

Bottom Line: Alternatively, individuals of the same species might compete over greater distances, known as heteromyopia, breaking down clusters and opening space for a second species to invade.This results in a common framework for predicting, given any pair of species and knowledge of the relevant parameters, whether they will coexist, the mechanism by which they will do so, and the resultant spatial pattern of the community.Spatial coexistence arises from complementary combinations of traits in each species rather than solely through self-limitation.

View Article: PubMed Central - PubMed

Affiliation: School of Physics & Astronomy, The University of Nottingham, University Park, Nottingham, NG7 2RD, United Kingdom; Facultad de Ciencias Físico Matemáticas, Universidad Autónoma de Puebla, 72001, Puebla, Pue., México.

ABSTRACT
Coexistence of apparently similar species remains an enduring paradox in ecology. Spatial structure has been predicted to enable coexistence even when population-level models predict competitive exclusion if it causes each species to limit its own population more than that of its competitor. Nevertheless, existing hypotheses conflict with regard to whether clustering favours or precludes coexistence. The spatial segregation hypothesis predicts that in clustered populations the frequency of intra-specific interactions will be increased, causing each species to be self-limiting. Alternatively, individuals of the same species might compete over greater distances, known as heteromyopia, breaking down clusters and opening space for a second species to invade. In this study we create an individual-based model in homogeneous two-dimensional space for two putative sessile species differing only in their demographic rates and the range and strength of their competitive interactions. We fully characterise the parameter space within which coexistence occurs beyond population-level predictions, thereby revealing a region of coexistence generated by a previously-unrecognised process which we term the triadic mechanism. Here coexistence occurs due to the ability of a second generation of offspring of the rarer species to escape competition from their ancestors. We diagnose the conditions under which each of three spatial coexistence mechanisms operates and their characteristic spatial signatures. Deriving insights from a novel metric - ecological pressure - we demonstrate that coexistence is not solely determined by features of the numerically-dominant species. This results in a common framework for predicting, given any pair of species and knowledge of the relevant parameters, whether they will coexist, the mechanism by which they will do so, and the resultant spatial pattern of the community. Spatial coexistence arises from complementary combinations of traits in each species rather than solely through self-limitation.

Show MeSH