Abstract. Predator outbreaks are predicted to increasingly decimate economically and ecologically important prey populations because global climate change and food-web modifications frequently facilitate predators and stress prey. Natural systems are organized hierarchically, with processes operating at multiple scales giving rise to patterns of biodiversity, so predicting and managing outbreaks requires a framework that accounts for the effects of both local and regional stressors. Here, we used the comparative experimental approach to investigate whether the collapse of a nationally important oyster fishery in the Gulf of Mexico (Apalachicola Bay, Florida) could have been (1) caused proximally by a predator outbreak and (2) whether this outbreak was mediated by local-and/or regional-scale forces. During the fishery collapse, we paired experiments with monitoring in Apalachicola Bay and found elevated water salinity, high abundance of predatory snails, and intense oyster mortality due to predation. By repeating these experiments over 4 yr, we found that periods of reduced water salinity inhibited predation on oysters. To partition the influence of local-versus-regional factors on this predator outbreak, we simultaneously replicated the paired experiments and monitoring in a nearby bay (Ochlockonee Bay) that shares the same regional-scale rainfall conditions. Increasing freshwater withdrawals from the watershed that drains into Apalachicola Bay have increased salinities in that bay, but there have not been similar withdrawals in the Ochlockonee Bay watershed. Therefore, Apalachicola Bay experienced a localized anthropogenic stress, while both bays experienced regional stress from drought. In Ochlockonee Bay, our experiments demonstrated that the river maintained sufficiently low salinity to provide~50% of oyster reefs with a refuge from predation. In contrast, salinity-dependent predation in Apalachicola Bay extended up to the river mouth. Given the stark differences in upstream water withdrawals between these watersheds, it is reasonable to surmise that these withdrawals exacerbated the stress of regional drought, created the difference in predation between the two bays, and thus may have precipitated the oyster fishery collapse. Our study provides empirical support for recent theory about the hierarchical organization of ecosystems, which predicts that stressors will interact across scales to cause localized predator outbreaks.

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Satiated predation, predation rate and prey preference of different weight groups of Rana tigrina (Daud) tadpoles on different larval and pupal stages of Culex fatigans were studied . Irrespective of the prey and predator size, the satiation time remained more or less equal . There exists a mass-dependent predation : Calculated predation rates or predatory constants (Kpr) showed that I instar prey was preyed upon at about equal rate, while other instars and pupa showed an increasing trend with increasing body weight of the predator. The prey preference assessed using the Kpr, revealed that prey size is an important parameter in predation . The R . tigrina tadpole is a more efficient pupal predator than other mosquito predators .

Extensive field observations were undertaken to study the population dynamics of the larvae of Catopsilia crocale in the Madurai Kamaraj University campus during the years 1980-81 and 1981-82. Though oligophagous, C. crocale adopted 'monophagic strategy' for oviposition and larval feeding. Seasonal changes in the nitrogen content of the food Cassia alata leaf influenced the pupal/adult weight and oviposition. Commencement of rain triggered the reproductive activity and continued precipitation facilitated maximum egg deposition. Of total egg production in a year, about 80 % was oviposited during northeast monsoon (September-December) and the rest during the south-west monsoon (May-August). Egg, I instar, V instar and pupa suffered more mortality than the other life stages. Ofthe total number of eggs laid, about 1·01 o,~emerged as adult and 98·99~.~died during the process of larval and pupal development.

Preferential utilization of protein, fat and carbohydrate by different weight classes of Macropodus cupanus was studied exposing the fish to algal, animal and combined feed. Consumption and conversion of protein and fat was maximum in the liver fed group. At maximum feeding the small fish converted carbohydrate, fat and protein at an efficiency of 9.45. 26.55 and 18.29% respectively. The efficiency of conversion decreased with increasing body weight. At all feeding schedules carbohydrate was converted more or less efficiently. The fish exposed to minimum animal feed or 100% algal feed utilized almost equal amount of stored protein cr fat for maintenance metabolism.