Ontogenetic change in the effectiveness of camouflage: growth versus pattern matching in Fowler's toad

Background matching camouflage enables animals to evade detection with colours and patterns that resemble and blend into the environment. Effective concealment can, however, be difficult to achieve as natural backgrounds are often heterogeneous and frequently made up of spatially distinct microhabitats that differ in their visual characteristics. Many species make use of multiple microhabitat patches, and the ways in which an animal exploits different microhabitats will likely vary throughout its life cycle as behaviour, morphology and predation risk change. Here, we used the Fowler's toad, Anaxyrus fowleri, and its lakeshore habitat to investigate how camouflage changes throughout ontogeny in relation to a series of spatially structured microhabitats. These toads are predominantly light beige in colour with a haphazard pattern of brown spots. This pattern is consistent throughout life, and spot size scales along with increasing body size. We modelled how well toad colour and patterning matched each background as perceived by bird, snake and mammal predators. We predicted that background matching would be targeted to the microhabitats where toads are most likely to be found during the day and that camouflage would be most effective at the most vulnerable (i.e. younger) life stages. We found that toad colour was specialized to match the dry sandy beach microhabitats where the toads were most frequently encountered and that pattern matching varied depending on toad size. We found that the small spots of juvenile toads best matched areas of bare sand whereas the correspondingly large spots of adult toads best matched larger items of beach debris such as broken shells, pebbles and fragments of wood. Taken together, our data suggest that, as toads grow larger, background matching camouflage remains effective, and that juveniles and adults use the same pattern to match different components within the heterogenous background. •In variable environments, camouflage can either be specialized or generalized.•Changes in body size can affect the efficacy of specialist or generalist camouflage.•Fowler’s toad camouflage is specialized to behaviourally important microhabitats.•As Fowler’s toads grow, their coloration matches different parts of the background.•Understanding camouflage requires defining both the spatial and temporal context.