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Feeding across the food web: The interaction between diet, movement and body size in estuarine crocodiles ( C rocodylus porosus )
Author(s) -
Hanson Jeffrey O.,
Salisbury Steven W.,
Campbell Hamish A.,
Dwyer Ross G.,
Jardine Timothy D.,
Franklin Craig E.
Publication year - 2015
Publication title -
austral ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.688
H-Index - 87
eISSN - 1442-9993
pISSN - 1442-9985
DOI - 10.1111/aec.12212
Subject(s) - trophic level , biology , predation , population , ecology , estuary , generalist and specialist species , ecosystem , habitat , apex predator , crocodile , food web , zoology , demography , sociology
The estuarine crocodile ( C rocodylus porosus ) is an apex predator across freshwater, estuarine and coastal environments. The impact of a changing C . porosus population upon the ecosystem is unknown, but due to large ontogenetic changes in body mass (>1000‐fold) their impact may be wide reaching and substantial. Here we investigated the relationship between diet, movement and body size in a population of C . porosus inhabiting a tidal river in northern Australia. Subcutaneous acoustic transmitters and fixed underwater receivers were used to determine the activity space and movement patterns of 42 individuals (202–451 cm in total length). There was no size‐related spatial partitioning among different sized crocodiles. Large individuals (snout–vent length ( SVL ): 160 cm < SVL < 188.5 cm) did, however, exhibit a much larger activity space than other size classes. Diet and individual specialization was assessed using the composition of stable carbon ( δ 13 C ) and nitrogen ( δ 15 N ) isotopes in tissues with different turnover rates. There was a quadratic relationship between body size and δ 15 N , suggesting that medium‐sized individuals (110 cm < SVL < 160 cm) incorporated a greater proportion of high trophic prey into their diets than small ( SVL < 110 cm) or large individuals ( SVL > 160 cm). Tissue δ 13 C composition on the other hand was positively correlated with body size, indicating that different size classes were trophically linked to primary producers in different habitats. Individual‐level analyses showed that small crocodiles were generalist feeders while medium and large size classes specialized on particular prey items within the food webs they fed. The findings further our understanding of ontogenetic variation in C . porosus diet, and suggest that change in C . porosus population size or demographics may be influential at various levels across the local food web.