Food limitation was tested in the laboratory by individual growth and reproduction of two cladoceran species, Ceriodaphnia richardi and Daphnia gessneri, from the shallow tropical Brazilian Lake Monte Alegre. The cladocerans were fed cultivated green alga Scenedesmus spinosus in concentrations of 0.20, 0.10, 0.05, and 0.025 mg C l À1 . Higher biomass and growth rates occurred in the two highest-food concentrations; the two lowest ones negatively affected clutch size and first reproduction. The threshold food concentration is lower than 0.025 mg C l À1 and the incipient limiting level is a value between 0.10 and 0.20 mg C l À1 . The largest species, D. gessneri, was more sensitive to low food concentrations. The effects of low and high temperatures (19 and 27°C) were evaluated by life table experiments with three cladocerans from the lakeDaphnia ambigua, D. gessneri, and Moina micrurawith no food limitation (1 mg C l À1 of S. spinosus). Higher population growth rates for the three species were found at 27°C; better performance in most life table parameters was observed for the former two species at the highest temperature, D. gessneri being the most sensitive to the lowest temperature. There are indications that temperature is an important abiotic factor that constrains populations of cladocerans for a short period in winter in the lake, when temperature decreases to 18-19°C. However, its influence cannot be separated from a biotic factor such as food, whose effect is stronger in the cool season, when concentrations are lower and contribution of inedible algae is relatively higher.

INTRODUCTIONLong-term studies are essential for understanding ecological processes such as the influence of stressors and are basic for modeling, but are few in number because of their inherent difficulties, including costs (Jackson and Füreder, 2006;Maberly and Elliott, 2012). In particular, long-term studies of zooplankton can reveal the influence of past factors, including management decisions (Hambright, 2008). Some causes of changes in the zooplankton that are perceptible over a longer period include alterations of abiotic factors or predator invasion (Yan et al., 2008).The factors that affect the diversity and size of zooplankton species are intriguing issues, but still subject to controversy. From the classic paper by Brooks and Dodson (1965) to recent studies, several factors have been contemplated, and temperature has emerged as the preponderant factor for explaining latitudinal differences in zooplankton body size (Gillooly and Dodson, 2000). Gillooly and Dodson compared more than 1100 lakes located between 81°N and 77°S latitude, and found that the size variation of cladoceran species was related to latitude, with smaller sizes in the tropics and the Arctic and a greater difference between the tropics and the temperate zone. According to these authors, the highest mean sizes were observed between 6°C and 8°C, declining at higher or lower temperatures. Havens et al. (2015), comparing 122 lakes located from 6° to 74°N and from 19° to 21°S, showed a relationship between size (as weight) of cladocerans and cyclopoid copepods and temperature. In contrast, Iglesias et al. (2011) suggested that predation by fish is the major factor explaining the smaller size of zooplankton in warm lakes. Hart and Bychek (2011), in their extensive review of the many factors that could potentially influence zooplankton size, addressed extrinsic factors such as temperature, food and predation, amongst others, besides intrinsic ones. The authors concluded, however, that although a general pattern may occur, different results can arise from distinct ecosystems.J. Limnol., 2015; 74(3): 606-617 ORIGINAL ARTICLE DOI: 10.4081/jlimnol.2015DOI: 10.4081/jlimnol. .1132 A long-term study on crustacean plankton of a shallow tropical lake: the role of invertebrate predation

Microcrustaceans and predators: diel migration in a tropical lake and comparison with shallow warm lakesDiel horizontal migration (DHM) and diel vertical migration (DVM) of planktonic microcrustaceans and invertebrate predators were studied simultaneously in a tropical shallow lake. DHM was not performed, and DVM was irregularly performed by the species. DHM of microcrustaceans does not seem to replace DVM as a strategy for decreasing predation risk in this shallow lake. The invertebrate predators, the IV instar of Chaoborus brasiliensis and the water mite Krendowskia sp., were mostly limnetic, the latter undergoing a nocturnal DVM that was not evident for the chaoborid larvae because a portion of the individuals remained in the water column in the daytime. DVM of some microcrustaceans, such as Ceriodaphnia richardi, Daphnia ambigua, Daphnia gessneri, and Thermocyclops decipiens, decreased the overlap with predators. Other behaviours, such as onshore location and occupation of the uppermost layers, seem to be more effective for coping with predation by limnetic invertebrate predators. Dissolved oxygen is a counteracting factor for only the vertical distribution because its concentration is low near the bottom in summer but not in the littoral zone. The lack of DHM in this study agrees with the results of most warm shallow lakes.