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FACTORS AFFECTING THE DISTRIBUTION AND CO-OCCURRENCE OF TWO SOUTHERN CALIFORNIAN ANOSTRACANS (BRANCHIOPODA), BRANCHINECTA SANDIEGONENSIS AND STREPTOCEPHALUS WOOTTONI

1996; Oxford University Press; Volume: 16; Issue: 4 Linguagem: Inglês

10.1163/193724096x00757

1937-240X

Stacie A. Hathaway, Marie A. Simovich,

Marine and coastal ecosystems

We address the role of temperature and maturation rate in limiting the distribution and co-occurrence of 2 ephemeral pool branchiopods, Branchinecta sandiegonensis and Streptocephalus woottoni (Anostraca), in southern California. Branchinecta sandiegonensis occurs in pools of variable depth (from 30 cm) and duration, while Streptocephalus woottoni is found only in deeper pools (>30 cm) of longer duration. These 2 species co-occur in a few pools, but their adults are never observed simultaneously. To better understand these patterns, fieldcollected cysts of both species were hatched at an array of constant and 12-h fluctuating temperatures. Maturation rates were compared in aquaria at room temperature (∼20―22°C) and by field observation. Both species hatched best at cooler temperatures (10°C and fluctuating 5― 15°C), but S. woottoni was more eurythermal. Both were inhibited at higher temperatures unless these temperatures were included in a fluctuating regime. After hatching, B. sandiegonensis did not mature at 5°C. In laboratory and field observations, B. sandiegonensis matured quickly (1― 2 weeks) at moderate temperatures and died before S. woottoni reached maturity. These results indicate that temperature plays a role in restricting the distribution of these species to the coast, where temperatures are favorable. Slower maturation rate helps to explain the absence of S. woottoni from shallow, potentially short-lived pools and why the 2 species co-occur but do not coexist as adults in deeper pools.