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Fear is a powerful force. The perceived threat of predation and competition can cause behavioural and physiological changes that ultimately affect fitness. Fear of predation may result in decreased foraging, increased hiding, or energetically-costly defense mechanisms, while intraspecific competition may lead to risky mating efforts. I investigated the impact of perceived predation and competition on the growth, behaviour, and fecundity of fall field crickets (Gryllus pennsylvanicus). This study is the first to manipulate both perceived predation and competition while measuring multiple impacts, allowing a holistic perspective. Using four treatments of control, predation, competition, and predation+competition, I exposed juvenile crickets to visual, chemical, and auditory cues (recordings of bird predators and male crickets) from their 4th instar to adulthood. I tracked growth measures such as mass, size, and development time until adulthood, then conducted behavioural assays and dissections to determine reproductive investment. My results showed that indirect predation and competition have substantial impacts. Perceived competition led to significantly decreased growth and food intake, while perceived predation led to anti-predator behaviour in females, which showed a trend of exiting from a vial faster. Both perceived predation and competition led to reduced reproductive investment, indicating a fecundity cost. These findings show that perceived risk alone can have wide-ranging impacts, expanding our understanding of indirect predation and competition effects.

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