Seasonal variation in natural populations of Drosophila spp. (Diptera) in two woodlands in the State of São Paulo, Brazil

Abstract

ABSTRACT. The composition and the seasonality of the natural populations of Drosophila species in relation to the climatic variables temperature and rainfall were analyzed from September 1998 through October 1999 by monthly collections, in two woodlands in the Northwest of the State of São Paulo, Brazil. The diversity dominance component curves were inclined, reflecting low diversity and high dominance of few species. Among the 25 species recorded, Drosophila sturtevanti Duda, 1927 was the most frequent and abundant. On the opposite to data in literature, D. paranaensis Barros, 1950 abundance and frequency were greater than those from D. mercatorum Patterson & Wheeler, 1942. A positive correlation between abundance and rainfall was observed for D. nebulosa Sturtevant, 1916. These data are indicative of changes in the populations structure due to new adaptive strategies arised in response to environmental modifications. Populations are entities in a state of change. Even when the community and the ecosystem appear not to change, the density, mortality, survival, age distribution, growth rate and other attributes of the component populations generally fluctuate, as species adjust constantly to the seasons, physical forces and to each other. Consequently, it is much more revealing to discover in what way and how quickly a given population is changing than what its size and composition may be at a certain moment (ODUM, 1988). KEYWORDS.In the natural world, it is important to distinguish between seasonal changes in the size of a population, largely controlled by seasonal adaptations linked to environmental factors, and annual fluctuations. Annual fluctuations may be considered in two categories: those controlled principally by annual differences in extrinsic factors such as temperature and rainfall, which are beyond the sphere of population interactions, and intrinsic factors, oscillations controlled principally by population dynamics, like biotic factors, such as the availability of food or energy. In many cases, year-on-year changes in abundance appear to be clearly correlated to variation in one or more of the principle extrinsic limiting factors, but some species maintain such a regular relative abundance, apparently irrespective of obvious environmental factors, that the term "cycles" appears to be appropriate. Species that have such a regular variation in population size are often described as "cyclical". Populations modify and compensate for the perturbations of physical factors, thus, the more organized and mature the community, or the more stable the physical environment, or both, the less will be the amplitude of the fluctuations in population density over time (KREBS, 1985).According to BRNCIC et al. (1985) the seasonality of each species in the natural world is the result of a long and continuous process of adaptation to environmental conditions in which the species usually lives.Flies of the Drosophila genus are appropriate for the study of population fluctuation, as they are insects highly sensitive to ...

Seasonality in insect abundance in the "Cerrado" of Goiás State, Brazil

“…Some other studies in Brazil have shown that even within a single family or genus, there are large seasonal variations of Diptera abundance, with some species being more abundant in drier periods and others in wetter ones (Torres & Madi-Ravazzi 2006;Oliveira et al 2007a). The Diptera form a group with very heterogeneous habitats and feeding habits.…”

“…The distribution, abundance and richness of insect species can be influenced by the climate, vegetation and their interactions (Wolda 1978;Marinoni & Ganho 2003;Kittelson 2004;Torres & Madi-Ravazzi 2006). Food resources and climate conditions vary in space and time, directly affecting the diversity and distribution of insect populations (Morais et al 1999;Kittelson 2004;Bispo et al 2006;Bispo & Oliveira 2007;Goldsmith 2007).…”

“…Food resources and climate conditions vary in space and time, directly affecting the diversity and distribution of insect populations (Morais et al 1999;Kittelson 2004;Bispo et al 2006;Bispo & Oliveira 2007;Goldsmith 2007). Climate is one of the determining factors in insect population fluctuations during the year (Wolda 1978;Torres & Madi-Ravazzi 2006).…”

On the use of open or closed traps in the capture of drosophilids

“…A track with 100 m of extension was established in each region, a collection point being demarcated at each ten meters (Figure 1). In each point, two traps, being an open (visitation, described in Torres & Madi-Ravazzi 2006) and another closed (apprehension, described in Medeiros & Klackzo 1999), were placed, at about 1.5 m from of the soil, hung on tree branches, and distant about two meters from each other (Figure 2a,b). The traps contained bait prepared with macerated banana and biological yeast (Saccharomyces cerevisiae) and remained in the collection places for a period of three days.…”

“…Although these collecting methods do not allow estimating the population density, it allows estimating the availability of these organisms for accessing a certain resource (bait) (Southwood 1978). In addition to the population size, other factors affect the capture of the flies, such as the presence of other natural resources, which compete with the bait, the activity of the flies in the sampled period (Klaczko et al 1983, Medeiros 2000, the part of the day in which the collection was done , Belo & Oliveira 1978 and the spatial distribution in the space (horizontal: , Pavan 1959, Medeiros 2000, Torres & Madi-Ravazzi 2006and vertical: Parsons 1975, Sene et al 1981, Kratz et al 1982, Tidon-Sklorz & Sene 1992. Such factors may interfere in the estimative of Drosophila population parameters, sometimes hiding information or creating false standards.…”