EFFECTS OF PREDATOR-RELATED CHEMICAL CUES ON THE ACTIVITY LEVEL OF HOUSTON TOAD (BUFO [ANAXYRUS] HOUSTONENSIS) AND COASTAL PLAIN TOAD (BUFO [INCILIUS] NEBULIFER) TADPOLES
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Predation is a strong ecological force and plays a role in shaping communities. In response to predation, many prey species have evolved predator avoidance mechanisms. One such avoidance mechanism is the detection of chemical cues from predators. This mechanism of predator detection is especially important in aquatic systems. Many anuran larvae can detect chemical cues created by the presence of aquatic invertebrate predators and consumption of conspecific and/or concurrent anurans by these same predators. A commonly documented larval anuran response to the presence of predator-related chemical cues is the reduction of activity. Two species that have not been tested for antipredator response in the presence of chemical cues during their larval stage are the coastal plain toad (Bufo [Incilius] nebulifer) and the federally endangered Houston toad (Bufo [Anaxyrus] houstonensis). I conducted two experiments. In the first, I tested if B. nebulifer exhibited a reduction of activity (antipredator response) in the presence of chemical cues produced from the presence of an invertebrate predator (kairomone cues) or chemical cues produced from the predation of conspecifics by an invertebrate predator (conspecific diet cues). I also examined whether aggregation status (solo tadpoles vs. groups of tadpoles) mediated the response of B. nebulifer to both cues. In the second experiment, I tested if B. houstonensis exhibited a reduction of activity (antipredator response) in the presence of kairomone cues, conspecific diet cues, or congeneric diet cues produced from the predation of larval B. nebulifer. I found that individuals and groups of B. nebulifer tadpoles reduced their activity level when exposed to conspecific diet cues, but only individuals reduced their activity level when exposed to kairomone cues. I found that B. houstonensis larvae lowered their activity in the presence of conspecific diet cues and congeneric diet cues, but not in the presence of kairomone cues. Taken together, these results imply a stronger response by both bufonids to predation than to the presence of a predator alone. I propose some possible hypotheses for the disparity in activity levels between solo and group treatments, diet and kairomone cues, and discuss the ecological implications of these disparities.