Laura Southcott - Academia.edu (original) (raw)

Papers by Laura Southcott

Evolution, 2012

Intraguild predation-competition and predation by the same antagonist-is widespread, but its evol... more Intraguild predation-competition and predation by the same antagonist-is widespread, but its evolutionary consequences are unknown. Intraguild prey may evolve antipredator defenses, superior competitive ability on shared resources, or the ability to use an alternative resource, any of which may alter the structure of the food web. We tested for evolutionary responses by threespine stickleback to a benthic intraguild predator, prickly sculpin. We used a comparative morphometric analysis to show that stickleback sympatric with sculpin are more armored and have more limnetic-like body shapes than allopatric stickleback. To test the ecological implications of this shift, we conducted a mesocosm experiment that varied sculpin presence and stickleback population of origin (from one sympatric and one allopatric lake). Predation by sculpin greatly increased the mortality of allopatric stickleback. In contrast, sculpin presence did not affect the mortality of sympatric stickleback, although they did have lower growth rates suggesting increased nonpredatory effects of sculpin. Consistent with their morphology, sympatric stickleback included more pelagic prey in their diets, leading to depletion of zooplankton in the mesocosms. These findings suggest that intraguild prey evolution has altered food web structure by reducing both predation by the intraguild predator and diet overlap between species.

Biological Journal of the Linnean Society, 2013

Reproductive isolation is central to the study of speciation. Multiple isolating barriers may pre... more Reproductive isolation is central to the study of speciation. Multiple isolating barriers may prevent species from hybridizing, although their individual strength and the interactions between them are rarely measured. We quantified habitat isolation in a recently diverged threespine stickleback species pair (Gasterosteus aculeatus complex) and controlled for any such interactions. Using enclosures in an outdoor pond, we confirm that males of the two species strongly prefer different nesting habitats: limnetic males build nests in open habitats, whereas benthic males nest under vegetation. However, forcing males to nest in their nonpreferred habitat did not reduce the probability of spawning by females. As a result, habitat isolation between the species is estimated to be weak. We compared the strength of habitat isolation estimated in the present study with estimates of other behavioural barriers using previously published data. We discovered that, although total mating isolation between the species is strong, the contributions of differences in body size and male nuptial colour are similarly individually weak. Instead, interactions with other, undetermined species-specific traits were responsible for most of the isolation resulting from differences in body size and, in benthics, colour. This is one of the first attempts to estimate individual isolating barriers at the same time as controlling for interactions.

Marine Ecology Progress Series, 2008

An age-at-length relationship was generated for the tiny Indo-Pacific coral reef goby Trimma nasa... more An age-at-length relationship was generated for the tiny Indo-Pacific coral reef goby Trimma nasa using presumed daily increment counts of sagittal otoliths from 110 specimens captured in Palau in May 2007. From these data, the estimated maximum age was approximately 87 d, and the average length of the pelagic larval duration was 33.9 ± 3.7 d (SD), nearly 39% of the maximum lifespan. Linear and power regression lines fit the data equally well (r 2 = 0.8458 and 0.8464, respectively). Mixed model analysis of age, length and sex data produced a better fit, with significant effects of age (p < 0.0001), sex (p = 0.0134) and age × sex interaction (p = 0.0059) on standard length. Males were significantly smaller than females and juveniles when corrected for age (p < 0.05). The male age-at-length relationship was also significantly different from those of females (p = 0.0218) and juveniles (p = 0.0066). Daily mortality rate as calculated by Hoenig's equation was 4.7%. These findings are in keeping with an increasing body of data demonstrating that small reef fish lead short lives with linear growth and high mortality, with important consequences for their contribution to the biomass and, hence, energy production of coral reefs.

Evolution, 2012

Intraguild predation-competition and predation by the same antagonist-is widespread, but its evol... more Intraguild predation-competition and predation by the same antagonist-is widespread, but its evolutionary consequences are unknown. Intraguild prey may evolve antipredator defenses, superior competitive ability on shared resources, or the ability to use an alternative resource, any of which may alter the structure of the food web. We tested for evolutionary responses by threespine stickleback to a benthic intraguild predator, prickly sculpin. We used a comparative morphometric analysis to show that stickleback sympatric with sculpin are more armored and have more limnetic-like body shapes than allopatric stickleback. To test the ecological implications of this shift, we conducted a mesocosm experiment that varied sculpin presence and stickleback population of origin (from one sympatric and one allopatric lake). Predation by sculpin greatly increased the mortality of allopatric stickleback. In contrast, sculpin presence did not affect the mortality of sympatric stickleback, although they did have lower growth rates suggesting increased nonpredatory effects of sculpin. Consistent with their morphology, sympatric stickleback included more pelagic prey in their diets, leading to depletion of zooplankton in the mesocosms. These findings suggest that intraguild prey evolution has altered food web structure by reducing both predation by the intraguild predator and diet overlap between species.

Biological Journal of the Linnean Society, 2013

Reproductive isolation is central to the study of speciation. Multiple isolating barriers may pre... more Reproductive isolation is central to the study of speciation. Multiple isolating barriers may prevent species from hybridizing, although their individual strength and the interactions between them are rarely measured. We quantified habitat isolation in a recently diverged threespine stickleback species pair (Gasterosteus aculeatus complex) and controlled for any such interactions. Using enclosures in an outdoor pond, we confirm that males of the two species strongly prefer different nesting habitats: limnetic males build nests in open habitats, whereas benthic males nest under vegetation. However, forcing males to nest in their nonpreferred habitat did not reduce the probability of spawning by females. As a result, habitat isolation between the species is estimated to be weak. We compared the strength of habitat isolation estimated in the present study with estimates of other behavioural barriers using previously published data. We discovered that, although total mating isolation between the species is strong, the contributions of differences in body size and male nuptial colour are similarly individually weak. Instead, interactions with other, undetermined species-specific traits were responsible for most of the isolation resulting from differences in body size and, in benthics, colour. This is one of the first attempts to estimate individual isolating barriers at the same time as controlling for interactions.

Marine Ecology Progress Series, 2008

An age-at-length relationship was generated for the tiny Indo-Pacific coral reef goby Trimma nasa... more An age-at-length relationship was generated for the tiny Indo-Pacific coral reef goby Trimma nasa using presumed daily increment counts of sagittal otoliths from 110 specimens captured in Palau in May 2007. From these data, the estimated maximum age was approximately 87 d, and the average length of the pelagic larval duration was 33.9 ± 3.7 d (SD), nearly 39% of the maximum lifespan. Linear and power regression lines fit the data equally well (r 2 = 0.8458 and 0.8464, respectively). Mixed model analysis of age, length and sex data produced a better fit, with significant effects of age (p < 0.0001), sex (p = 0.0134) and age × sex interaction (p = 0.0059) on standard length. Males were significantly smaller than females and juveniles when corrected for age (p < 0.05). The male age-at-length relationship was also significantly different from those of females (p = 0.0218) and juveniles (p = 0.0066). Daily mortality rate as calculated by Hoenig's equation was 4.7%. These findings are in keeping with an increasing body of data demonstrating that small reef fish lead short lives with linear growth and high mortality, with important consequences for their contribution to the biomass and, hence, energy production of coral reefs.