Climate change has strong potential to modify the structure and functioning of ecosystems, but ex... more Climate change has strong potential to modify the structure and functioning of ecosystems, but experimental field studies into its effects are rare. On rocky shores, grazing limpets strongly affect ecosystem structure and their distribution in NW Europe is changing in response to climate change. Three limpet species co-occur in SW Britain (Patella vulgata, Patella ulyssiponensis and Patella depressa) on open rock and in pools. Shores in Ireland are similar, but currently lack P. depressa. It is anticipated that P. depressa will expand its range into Ireland as the climate warms, but we currently lack an empirical basis to predict the consequences of this change. Recent studies show that increasing abundance of P. depressa on British shores has been accompanied by a decline of P. vulgata suggesting interspecific competition. In this study, a new experimental framework was used to examine the potential for P. depressa to affect P. vulgata on Irish shores. P. vulgata was experimentally transplanted into enclosures on open rock and in pools in both Ireland and Britain. In pools, treatments also included transplanted P. ulyssiponensis to mimic natural assemblages. Growth and mortality of P. vulgata were measured over 6 months with no differences between Ireland and Britain. In Britain, P. vulgata caged in pools with transplanted P. depressa and P. ulyssiponensis showed reduced growth, compared with when caged in pools with P. ulyssiponensis alone. There was no effect of P. depressa on the growth rate of P. vulgata on open rock. Results indicate that if the range of P. depressa extends into Ireland, it would reduce the growth of P. vulgata where it co-occurs with P. ulyssiponensis in pools. The framework used here provides a field-based approach that could be used to examine the impacts of climateinduced range expansions on the structure and functioning of other ecosystems.
Biodiversity is defined by the scales at which organisms coexist. Coexistence at larger spatial s... more Biodiversity is defined by the scales at which organisms coexist. Coexistence at larger spatial scales may be underpinned by segregation at smaller spatial scales or temporal variability in behaviour and/ or distribution. Limpets of the genus Patella are keystone grazers controlling the growth of macroalgae on many rocky shores. This study examined the distribution and abundance of P. vulgata and P. ulyssiponensis in relation to habitat and to each other at a range of spatial scales. Limpets were sampled on four shores on each of the east and west coasts of Ireland, in two different transects (10 m apart) at each of three shore heights in winter 2003 and summer 2004. P. vulgata and P. ulyssiponensis coexist around the coast of Ireland, but on shores where they co-occur, the pattern of coexistence begins to break down at the level of shore height: P. ulyssiponensis were more abundant on the low-shore than mid-shore, and P. vulgata were distributed evenly throughout the low and the midshore. At the level of habitat (pools vs. open rock), the two species exhibited a high degree of segregation: P. vulgata of all sizes were more common on open rock and P. ulyssiponensis of all sizes were more common in pools. The presence or absence of P. ulyssiponensis had no effect on the distribution of juvenile P. vulgata with respect to pools. Unexpectedly, however, a greater proportion of adult P. vulgata were found in pools at sites where P. ulyssiponensis were present in the pools than at sites where they were absent. The results of this study emphasize the need for multiple-scale analyses of the distribution and abundance of organisms to understand the organisation of natural assemblages.
Identifying the mechanisms that underpin species richness is one of the central issues of communi... more Identifying the mechanisms that underpin species richness is one of the central issues of community ecology. On rocky shores in north-western Europe, two key limpet species coexist on the mid-and low shore but are segregated at small scales with respect to habitat. Shortterm and long-term experiments were done to test whether habitat suitability or habitat-speciWc competition drives the small-scale segregation of these species and therefore underpins their coexistence at larger spatial scales. In a controlled short-term experiment, Patella vulgata was transplanted onto open rock and into pools that either contained Patella ulyssiponensis and/or their mucus or from which P. ulyssiponensis and/or their mucus had been removed. After 2 days, P. vulgata remained in all experimental plots in similar numbers irrespective of treatment indicating that there was no negative response to P. ulyssiponensis, mucus or the pool habitat. In a long-term experiment, cage enclosures containing both species were set up in pools and on open rock over a 6-month period. P. vulgata grew equally well on both open rock and in pools but suVered higher mortality in pools. P. ulyssiponensis showed lower growth rate and higher mortality on open rock than in pools. P. ulyssiponensis exhibited increased growth in higher intraspeciWc densities on open rock and reduced growth in higher intraspeciWc densities in pools, indicating some degree of intraspeciWc facilitation on open rock and intra-speciWc competition in pools. There was no evidence of interspeciWc competition either in the short term or in the long term. Results revealed that habitat suitability was the mechanism causing segregation of these species at smaller spatial scales enabling them to coexist at larger spatial scales. ConXicting results in the short-term and long-term experiments highlight the importance of considering the correct temporal extent for experimental tests of hypotheses.
Philosophical Transactions of the Royal Society B: Biological Sciences, 2012
Climate change has complex structural impacts on coastal ecosystems. Global warming is linked to ... more Climate change has complex structural impacts on coastal ecosystems. Global warming is linked to a widespread decline in body size, whereas increased flood frequency can amplify nutrient enrichment through enhanced run-off. Altered population body-size structure represents a disruption in top-down control, whereas eutrophication embodies a change in bottom-up forcing. These processes are typically studied in isolation and little is known about their potential interactive effects. Here, we present the results of an in situ experiment examining the combined effects of topdown and bottom-up forces on the structure of a coastal marine community. Reduced average body mass of the top predator (the shore crab, Carcinus maenas) and nutrient enrichment combined additively to alter mean community body mass. Nutrient enrichment increased species richness and overall density of organisms. Reduced top-predator body mass increased community biomass. Additionally, we found evidence for an allometrically induced trophic cascade. Here, the reduction in top-predator body mass enabled greater biomass of intermediate fish predators within the mesocosms. This, in turn, suppressed key micrograzers, which led to an overall increase in microalgal biomass. This response highlights the possibility for climate-induced trophic cascades, driven by altered size structure of populations, rather than species extinction.
Climate change has strong potential to modify the structure and functioning of ecosystems, but ex... more Climate change has strong potential to modify the structure and functioning of ecosystems, but experimental field studies into its effects are rare. On rocky shores, grazing limpets strongly affect ecosystem structure and their distribution in NW Europe is changing in response to climate change. Three limpet species co-occur in SW Britain (Patella vulgata, Patella ulyssiponensis and Patella depressa) on open rock and in pools. Shores in Ireland are similar, but currently lack P. depressa. It is anticipated that P. depressa will expand its range into Ireland as the climate warms, but we currently lack an empirical basis to predict the consequences of this change. Recent studies show that increasing abundance of P. depressa on British shores has been accompanied by a decline of P. vulgata suggesting interspecific competition. In this study, a new experimental framework was used to examine the potential for P. depressa to affect P. vulgata on Irish shores. P. vulgata was experimentally transplanted into enclosures on open rock and in pools in both Ireland and Britain. In pools, treatments also included transplanted P. ulyssiponensis to mimic natural assemblages. Growth and mortality of P. vulgata were measured over 6 months with no differences between Ireland and Britain. In Britain, P. vulgata caged in pools with transplanted P. depressa and P. ulyssiponensis showed reduced growth, compared with when caged in pools with P. ulyssiponensis alone. There was no effect of P. depressa on the growth rate of P. vulgata on open rock. Results indicate that if the range of P. depressa extends into Ireland, it would reduce the growth of P. vulgata where it co-occurs with P. ulyssiponensis in pools. The framework used here provides a field-based approach that could be used to examine the impacts of climateinduced range expansions on the structure and functioning of other ecosystems.
Biodiversity is defined by the scales at which organisms coexist. Coexistence at larger spatial s... more Biodiversity is defined by the scales at which organisms coexist. Coexistence at larger spatial scales may be underpinned by segregation at smaller spatial scales or temporal variability in behaviour and/ or distribution. Limpets of the genus Patella are keystone grazers controlling the growth of macroalgae on many rocky shores. This study examined the distribution and abundance of P. vulgata and P. ulyssiponensis in relation to habitat and to each other at a range of spatial scales. Limpets were sampled on four shores on each of the east and west coasts of Ireland, in two different transects (10 m apart) at each of three shore heights in winter 2003 and summer 2004. P. vulgata and P. ulyssiponensis coexist around the coast of Ireland, but on shores where they co-occur, the pattern of coexistence begins to break down at the level of shore height: P. ulyssiponensis were more abundant on the low-shore than mid-shore, and P. vulgata were distributed evenly throughout the low and the midshore. At the level of habitat (pools vs. open rock), the two species exhibited a high degree of segregation: P. vulgata of all sizes were more common on open rock and P. ulyssiponensis of all sizes were more common in pools. The presence or absence of P. ulyssiponensis had no effect on the distribution of juvenile P. vulgata with respect to pools. Unexpectedly, however, a greater proportion of adult P. vulgata were found in pools at sites where P. ulyssiponensis were present in the pools than at sites where they were absent. The results of this study emphasize the need for multiple-scale analyses of the distribution and abundance of organisms to understand the organisation of natural assemblages.
Identifying the mechanisms that underpin species richness is one of the central issues of communi... more Identifying the mechanisms that underpin species richness is one of the central issues of community ecology. On rocky shores in north-western Europe, two key limpet species coexist on the mid-and low shore but are segregated at small scales with respect to habitat. Shortterm and long-term experiments were done to test whether habitat suitability or habitat-speciWc competition drives the small-scale segregation of these species and therefore underpins their coexistence at larger spatial scales. In a controlled short-term experiment, Patella vulgata was transplanted onto open rock and into pools that either contained Patella ulyssiponensis and/or their mucus or from which P. ulyssiponensis and/or their mucus had been removed. After 2 days, P. vulgata remained in all experimental plots in similar numbers irrespective of treatment indicating that there was no negative response to P. ulyssiponensis, mucus or the pool habitat. In a long-term experiment, cage enclosures containing both species were set up in pools and on open rock over a 6-month period. P. vulgata grew equally well on both open rock and in pools but suVered higher mortality in pools. P. ulyssiponensis showed lower growth rate and higher mortality on open rock than in pools. P. ulyssiponensis exhibited increased growth in higher intraspeciWc densities on open rock and reduced growth in higher intraspeciWc densities in pools, indicating some degree of intraspeciWc facilitation on open rock and intra-speciWc competition in pools. There was no evidence of interspeciWc competition either in the short term or in the long term. Results revealed that habitat suitability was the mechanism causing segregation of these species at smaller spatial scales enabling them to coexist at larger spatial scales. ConXicting results in the short-term and long-term experiments highlight the importance of considering the correct temporal extent for experimental tests of hypotheses.
Philosophical Transactions of the Royal Society B: Biological Sciences, 2012
Climate change has complex structural impacts on coastal ecosystems. Global warming is linked to ... more Climate change has complex structural impacts on coastal ecosystems. Global warming is linked to a widespread decline in body size, whereas increased flood frequency can amplify nutrient enrichment through enhanced run-off. Altered population body-size structure represents a disruption in top-down control, whereas eutrophication embodies a change in bottom-up forcing. These processes are typically studied in isolation and little is known about their potential interactive effects. Here, we present the results of an in situ experiment examining the combined effects of topdown and bottom-up forces on the structure of a coastal marine community. Reduced average body mass of the top predator (the shore crab, Carcinus maenas) and nutrient enrichment combined additively to alter mean community body mass. Nutrient enrichment increased species richness and overall density of organisms. Reduced top-predator body mass increased community biomass. Additionally, we found evidence for an allometrically induced trophic cascade. Here, the reduction in top-predator body mass enabled greater biomass of intermediate fish predators within the mesocosms. This, in turn, suppressed key micrograzers, which led to an overall increase in microalgal biomass. This response highlights the possibility for climate-induced trophic cascades, driven by altered size structure of populations, rather than species extinction.
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