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Edge effects reverse facilitation by a widespread foundation species

View Article: PubMed Central - PubMed

ABSTRACT

Dense aggregations of foundation species often mitigate environmental stresses for organisms living among them. Considerable work documents such benefits by comparing conditions inside versus outside these biogenic habitats. However, environmental gradients commonly arise across the extent of even single patches of habitat-forming species, including cases where stresses diverge between habitat interiors and edges. We ask here whether such edge effects could alter how habitat-forming species influence residents, potentially changing the strength or direction of interactions (i.e., from stress amelioration to exacerbation). We take as a model system the classic marine foundation species, Mytilus californianus, the California mussel. Results demonstrate that mussel beds both increase and decrease thermal stresses. Over a distance of 6 to 10 cm from the bed interior to its upper surface, peak temperatures climb from as much as 20 °C below to 5 °C above those of adjacent bedrock. This directional shift in temperature modification affects interactions with juvenile mussels, such that thermal stresses and associated mortality risk are higher at the bed surface, but substantially reduced deeper within the adult matrix. These findings provide a case example of how stress gradients generated across biogenic habitats can markedly alter ecological interactions even within a single habitat patch.

No MeSH data available.


Related in: MedlinePlus

Incorporating edge effects into conceptual models of facilitation.Conceptual model depicting how edge effects could drive spatial heterogeneity in habitat modification within the domain of a habitat-former. The heavy black lines indicate, for each of two habitat types, a previously described pattern in which increased habitat density or size of an aggregation cause greater amelioration of environmental stress59. Dotted lines indicate ambient stress levels outside the biogenic habitat. As explored here, habitat modification could exacerbate environmental stresses as well as mitigate them (thin solid lines). (A) Case of a vertical core through a mussel bed in which interior locations experience reduced temperatures via shading and poor heat conduction, while the bed surface encounters elevated temperatures compared to nearby bedrock, as small, dark shells heat rapidly under solar radiation. In this first scenario, only interior reductions in temperature will likely depend on the density or size of the mussel bed. (B) An alternative example in which a biogenic habitat again ameliorates and exacerbates environmental stress simultaneously, but both processes depend on habitat density or size. Here, the tendency for a stand of forest trees to slow wind speeds in its interior increases with the density or spatial extent of the stand. Likewise, the tendency for the forest stand to divert winds around it and therefore induce flow acceleration along its edges rises as the density and/or dimensions of the stand increases.
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f6: Incorporating edge effects into conceptual models of facilitation.Conceptual model depicting how edge effects could drive spatial heterogeneity in habitat modification within the domain of a habitat-former. The heavy black lines indicate, for each of two habitat types, a previously described pattern in which increased habitat density or size of an aggregation cause greater amelioration of environmental stress59. Dotted lines indicate ambient stress levels outside the biogenic habitat. As explored here, habitat modification could exacerbate environmental stresses as well as mitigate them (thin solid lines). (A) Case of a vertical core through a mussel bed in which interior locations experience reduced temperatures via shading and poor heat conduction, while the bed surface encounters elevated temperatures compared to nearby bedrock, as small, dark shells heat rapidly under solar radiation. In this first scenario, only interior reductions in temperature will likely depend on the density or size of the mussel bed. (B) An alternative example in which a biogenic habitat again ameliorates and exacerbates environmental stress simultaneously, but both processes depend on habitat density or size. Here, the tendency for a stand of forest trees to slow wind speeds in its interior increases with the density or spatial extent of the stand. Likewise, the tendency for the forest stand to divert winds around it and therefore induce flow acceleration along its edges rises as the density and/or dimensions of the stand increases.

Mentions: Although such issues do not yet appear in most conceptual considerations of facilitation and its consequences, findings here suggest that incorporating within-patch stress gradients into ecological theory could lead to a richer understanding of organismal interactions. Facilitation by habitat modification is often conceived as driving monotonic decreases of environmental stresses within the spatial extent of a biogenic habitat, with such declines becoming more marked as the density or size of the habitat-former increases. By including the possibility of within-patch shifts in habitat modification, we can envision a broader set of spatially dependent interactions between habitat-users and habitat-formers (e.g., Fig. 6). Such details could be important for predicting population responses to a shifting climate in the many cases where habitat-formers have strong local effects on climate-related parameters such as temperature, humidity, precipitation, and water chemistry. Here, we found that quantifying a within-patch gradient in thermal stress enabled a clearer understanding of intraspecific relationships driving juvenile mortality risk in a dominant foundation species. Taken together, these findings underscore the benefits of including the sometimes dramatic and opposing patterns of habitat modification into efforts to identify relationships among, and vulnerabilities of, the numerous taxa associated with habitat-forming species.


Edge effects reverse facilitation by a widespread foundation species
Incorporating edge effects into conceptual models of facilitation.Conceptual model depicting how edge effects could drive spatial heterogeneity in habitat modification within the domain of a habitat-former. The heavy black lines indicate, for each of two habitat types, a previously described pattern in which increased habitat density or size of an aggregation cause greater amelioration of environmental stress59. Dotted lines indicate ambient stress levels outside the biogenic habitat. As explored here, habitat modification could exacerbate environmental stresses as well as mitigate them (thin solid lines). (A) Case of a vertical core through a mussel bed in which interior locations experience reduced temperatures via shading and poor heat conduction, while the bed surface encounters elevated temperatures compared to nearby bedrock, as small, dark shells heat rapidly under solar radiation. In this first scenario, only interior reductions in temperature will likely depend on the density or size of the mussel bed. (B) An alternative example in which a biogenic habitat again ameliorates and exacerbates environmental stress simultaneously, but both processes depend on habitat density or size. Here, the tendency for a stand of forest trees to slow wind speeds in its interior increases with the density or spatial extent of the stand. Likewise, the tendency for the forest stand to divert winds around it and therefore induce flow acceleration along its edges rises as the density and/or dimensions of the stand increases.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120328&req=5

f6: Incorporating edge effects into conceptual models of facilitation.Conceptual model depicting how edge effects could drive spatial heterogeneity in habitat modification within the domain of a habitat-former. The heavy black lines indicate, for each of two habitat types, a previously described pattern in which increased habitat density or size of an aggregation cause greater amelioration of environmental stress59. Dotted lines indicate ambient stress levels outside the biogenic habitat. As explored here, habitat modification could exacerbate environmental stresses as well as mitigate them (thin solid lines). (A) Case of a vertical core through a mussel bed in which interior locations experience reduced temperatures via shading and poor heat conduction, while the bed surface encounters elevated temperatures compared to nearby bedrock, as small, dark shells heat rapidly under solar radiation. In this first scenario, only interior reductions in temperature will likely depend on the density or size of the mussel bed. (B) An alternative example in which a biogenic habitat again ameliorates and exacerbates environmental stress simultaneously, but both processes depend on habitat density or size. Here, the tendency for a stand of forest trees to slow wind speeds in its interior increases with the density or spatial extent of the stand. Likewise, the tendency for the forest stand to divert winds around it and therefore induce flow acceleration along its edges rises as the density and/or dimensions of the stand increases.
Mentions: Although such issues do not yet appear in most conceptual considerations of facilitation and its consequences, findings here suggest that incorporating within-patch stress gradients into ecological theory could lead to a richer understanding of organismal interactions. Facilitation by habitat modification is often conceived as driving monotonic decreases of environmental stresses within the spatial extent of a biogenic habitat, with such declines becoming more marked as the density or size of the habitat-former increases. By including the possibility of within-patch shifts in habitat modification, we can envision a broader set of spatially dependent interactions between habitat-users and habitat-formers (e.g., Fig. 6). Such details could be important for predicting population responses to a shifting climate in the many cases where habitat-formers have strong local effects on climate-related parameters such as temperature, humidity, precipitation, and water chemistry. Here, we found that quantifying a within-patch gradient in thermal stress enabled a clearer understanding of intraspecific relationships driving juvenile mortality risk in a dominant foundation species. Taken together, these findings underscore the benefits of including the sometimes dramatic and opposing patterns of habitat modification into efforts to identify relationships among, and vulnerabilities of, the numerous taxa associated with habitat-forming species.

View Article: PubMed Central - PubMed

ABSTRACT

Dense aggregations of foundation species often mitigate environmental stresses for organisms living among them. Considerable work documents such benefits by comparing conditions inside versus outside these biogenic habitats. However, environmental gradients commonly arise across the extent of even single patches of habitat-forming species, including cases where stresses diverge between habitat interiors and edges. We ask here whether such edge effects could alter how habitat-forming species influence residents, potentially changing the strength or direction of interactions (i.e., from stress amelioration to exacerbation). We take as a model system the classic marine foundation species, Mytilus californianus, the California mussel. Results demonstrate that mussel beds both increase and decrease thermal stresses. Over a distance of 6 to 10 cm from the bed interior to its upper surface, peak temperatures climb from as much as 20 °C below to 5 °C above those of adjacent bedrock. This directional shift in temperature modification affects interactions with juvenile mussels, such that thermal stresses and associated mortality risk are higher at the bed surface, but substantially reduced deeper within the adult matrix. These findings provide a case example of how stress gradients generated across biogenic habitats can markedly alter ecological interactions even within a single habitat patch.

No MeSH data available.


Related in: MedlinePlus