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Predatory impact of two syntopic mudskippers on a brachyuran community in a tropical mangrove system
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Type
Thesis
Author
Su, Theresa Linting
Supervisor
Lim, Shirley S. L.
Abstract
Predator-prey interactions have been widely examined from a top-down approach of predatory effects on the prey community. A more comprehensive approach requires evaluating these interactions from both the predator and prey perspectives. In this study, the synecologies of two syntopic mudskippers (Gobiidae) and their brachyuran prey were investigated in a Singapore mangrove. The ecological niches of the mudskippers, Periophthalmodon schlosseri and Periophthalmus walailakae, were examined in terms of their distribution, diet and habitat selection. Effects on prey communities were discussed with reference to density and trait-mediated direct interactions with the two predators.
Reportedly segregated in Thai mangroves, coexistence of the two predators in Singapore mangroves was achieved through niche partitioning. Periophthalmodon schlosseri displayed variations in prey and habitat choices, characteristic of a generalist. In contrast Periophthalmus walailakae showed more specialised traits, inhabiting and foraging only in mangrove forests. In Lim Chu Kang mangrove, diets of the two predators were predominantly cancrivorous, evident of optimal foraging on the most abundant brachyuran prey species, Paracleistostoma depressum (Camptandriidae). With an extensive overlap in diet niche, temporal partitioning was attained during foraging bouts: Periophthalmodon schlosseri feeds earlier whereas Periophthalmus walailakae feeds later after tidal exposure. Competition was further alleviated through spatial partitioning: areas inhabited by Periophthalmodon schlosseri had higher siltation than Periophthalmus walailakae-inhabited sites.
As Periophthalmodon schlosseri is approximately twice the length of Periophthalmus walailakae, the disparity in nutritional needs is translated to predatory pressures of varying strengths. Predatory effects were detected through density-mediated interactions on the brachyuran prey population. In situ experimental work provided evidence for impacts on the Paracleistostoma depressum population through lowered densities and larger size distributions under high predation. However, predatory effects were indiscernible in the second most abundant brachyuran species, Haberma nanum (Sesarmidae).
Predator evasion behaviours were studied to understand the exertion of unequal selective pressures on the two prey species. Predator recognition was demonstrated in both species, but alternative evasion strategies were employed despite a common suite of anti-predatory behaviours. Paracleistostoma depressum reacts later in a predator-stimulated repertoire and is dependent on crypsis for protection, while Haberma nanum responds with flight upon encounter.
Bottom-up succession was described from a study of two trophic levels over a two-year biomonitoring study, following a one-time predator removal. The prey assemblage showed rapid recovery within five months from time of disturbance—recruitment was documented in the Paracleistostoma depressum population, reflecting increased size distributions with greater densities of smaller crab individuals. In contrast, mudskippers residing outside the emptied experimental plots displayed only transient use of the available space. Results suggest that the Lim Chu Kang mangrove is not at carrying capacity for the involved species, with potential to host more mesopredators (e.g., monitor lizards) or support larger apex predators (e.g., crocodiles).
While investigating the ecological framework of predator-prey interactions, this study presents a positive outlook for coastal preservation in Singapore. As the Lim Chu Kang mangrove remains part of an extensive estuarine coast, the potential of these mangroves to support higher trophic predators offers encouraging news with respect to conservation and management efforts.
Reportedly segregated in Thai mangroves, coexistence of the two predators in Singapore mangroves was achieved through niche partitioning. Periophthalmodon schlosseri displayed variations in prey and habitat choices, characteristic of a generalist. In contrast Periophthalmus walailakae showed more specialised traits, inhabiting and foraging only in mangrove forests. In Lim Chu Kang mangrove, diets of the two predators were predominantly cancrivorous, evident of optimal foraging on the most abundant brachyuran prey species, Paracleistostoma depressum (Camptandriidae). With an extensive overlap in diet niche, temporal partitioning was attained during foraging bouts: Periophthalmodon schlosseri feeds earlier whereas Periophthalmus walailakae feeds later after tidal exposure. Competition was further alleviated through spatial partitioning: areas inhabited by Periophthalmodon schlosseri had higher siltation than Periophthalmus walailakae-inhabited sites.
As Periophthalmodon schlosseri is approximately twice the length of Periophthalmus walailakae, the disparity in nutritional needs is translated to predatory pressures of varying strengths. Predatory effects were detected through density-mediated interactions on the brachyuran prey population. In situ experimental work provided evidence for impacts on the Paracleistostoma depressum population through lowered densities and larger size distributions under high predation. However, predatory effects were indiscernible in the second most abundant brachyuran species, Haberma nanum (Sesarmidae).
Predator evasion behaviours were studied to understand the exertion of unequal selective pressures on the two prey species. Predator recognition was demonstrated in both species, but alternative evasion strategies were employed despite a common suite of anti-predatory behaviours. Paracleistostoma depressum reacts later in a predator-stimulated repertoire and is dependent on crypsis for protection, while Haberma nanum responds with flight upon encounter.
Bottom-up succession was described from a study of two trophic levels over a two-year biomonitoring study, following a one-time predator removal. The prey assemblage showed rapid recovery within five months from time of disturbance—recruitment was documented in the Paracleistostoma depressum population, reflecting increased size distributions with greater densities of smaller crab individuals. In contrast, mudskippers residing outside the emptied experimental plots displayed only transient use of the available space. Results suggest that the Lim Chu Kang mangrove is not at carrying capacity for the involved species, with potential to host more mesopredators (e.g., monitor lizards) or support larger apex predators (e.g., crocodiles).
While investigating the ecological framework of predator-prey interactions, this study presents a positive outlook for coastal preservation in Singapore. As the Lim Chu Kang mangrove remains part of an extensive estuarine coast, the potential of these mangroves to support higher trophic predators offers encouraging news with respect to conservation and management efforts.
Date Issued
2016
Call Number
QL758 Su
Date Submitted
2016