MORRIS, D.M. 1987. Ecological scale and habitat use. Ecology 68(2):362-369
Abstract. Population density can respond to habitat at different scales. If habitat selection occurs as a consequence of resource exploitation, the density of fine-grained consumers should reflect microhabitat variation. But if habitat use is controlled by a variety of selective pressured, it is no longer apparent whether density should respond to micro- or macrohabitat. These two alternatives can be tested simultaneously by multiple regression models where macrohabitat are represented by dummy variables. When the local densities of two Temperate Zone rodents were analyzed in this way, macrohabitat and temporal effects were consistent significant predictors of rodent density; microhabitat was not. This analysis suggests species whose patterns of resource and habitat use probably depart from classical interpretations of species coexistence. It is probably premature to assess the role of habitat selection in the structure of ecological systems until the results of further tests of habitat scaling are reported.
sábado, 28 de julho de 2012
sábado, 21 de julho de 2012
Pseudoreplication and the design of ecological field experiments
HULBERT, S.H. 1984. Pseudoreplication and the design of ecological field experiments. Ecological Monographs 54(2):187-211.
Abstract. Pseudoreplication is defined as the use of inferential statistics to test for treatment effects with data from experiments where either treatments are not replicated (though samples may be) or replicates are not statistically independent. In ANOVA terminology, it is the testing for treatment effects with and error term inappropriate to the hypothesis being considered. Scrutiny of 176 experimental studies published between 1960 and the present revealed that pseudoreplication occurred in 27% of them, or 48% of all such studies that applied inferential staticts. The incidence of pseudoreplication is especially high in studies of marine benthos and small mammals. The critical features of controlled experimentation are reviewed. Nondemonic intrusion is defined as the impingement of chance events on and experiment in progress. As a safeguard against both it and preexisting gradients, interspersion of treatments is argued to be an obligatory feature of good design. Especially in small experiments, adequate interspersion can sometimes be assumed only by dispensing with strict randomization procedures. Comprehension of this conflict between interspersion and randomization is aided by distinguishing pre-layout (or conventional) and layout-specific alpha (probability of tyme I error). Suggestions are offered to statisticians and editors of ecological journals as to how ecologists' understanding of experimental design and statistics might be improved.
Abstract. Pseudoreplication is defined as the use of inferential statistics to test for treatment effects with data from experiments where either treatments are not replicated (though samples may be) or replicates are not statistically independent. In ANOVA terminology, it is the testing for treatment effects with and error term inappropriate to the hypothesis being considered. Scrutiny of 176 experimental studies published between 1960 and the present revealed that pseudoreplication occurred in 27% of them, or 48% of all such studies that applied inferential staticts. The incidence of pseudoreplication is especially high in studies of marine benthos and small mammals. The critical features of controlled experimentation are reviewed. Nondemonic intrusion is defined as the impingement of chance events on and experiment in progress. As a safeguard against both it and preexisting gradients, interspersion of treatments is argued to be an obligatory feature of good design. Especially in small experiments, adequate interspersion can sometimes be assumed only by dispensing with strict randomization procedures. Comprehension of this conflict between interspersion and randomization is aided by distinguishing pre-layout (or conventional) and layout-specific alpha (probability of tyme I error). Suggestions are offered to statisticians and editors of ecological journals as to how ecologists' understanding of experimental design and statistics might be improved.
sábado, 14 de julho de 2012
Habitat fragmentation and movements of three small mammals (Sigmodon, Microtus, and Peromyscus)
DIFFENDORFER, J.E.; GAINES, M.S.; HOLT, R.D. 1995. Habitat fragmentation and movements of three small mammals (Sigmodon, Microtus, and Peromyscus). Ecology 76(3):827-839.
Abstract. We studied the effects of habitat fragmentation on the movements of cotton rats (Sigmodon hispidus), deer mice (Peromyscus maniculatus), and prairie voles (Microtus ochrogaster) living in a fragmented landscape using 7.7 yr (1984-1992) of mark-recapture data. The study area included three kinds of 0.5-ha blocks: single large patches (5000 m²), clusters of medium patches (288 m²), and clusters of small patches (32 m²). We tested three predictions regarding animal movements. First, animal should move longer distances as fragmentation increases. Second, the proportion of animals moving will decrease as fragmentation increases. Third, species will show more movement from putative sources to putative sinks. In support of our first two predictions, all species (except male cotton rats) moved farther, and lower proportions of animals moved, as fragmentation increased. In testing our third prediction, we found no trends, for all species, between patch size and the net number of animals a block either imported or exported, indicating source-sink dynamics were probably not occurring on our study site. Furthermore, animals of all species (except female deer mice) switched more frequently to blocks of larger patches. For prairie voles in the spring and deer mice in the summer, relative abundance among blocks predicted from a Markov matrix model of switching probabilities showed high congruence with the actual abundances, indicating movement and abundance were related. In both cotton rats and prairie voles but not in deer mice, more juveniles and nonreproductive animals switched between blocks than did adults or reproductive animals. Deer mice switched more frequently than did either cotton rats or prairie voles; the latter species switched in similar frequencies. We discuss the implications of our data for modeling and conservation.
Abstract. We studied the effects of habitat fragmentation on the movements of cotton rats (Sigmodon hispidus), deer mice (Peromyscus maniculatus), and prairie voles (Microtus ochrogaster) living in a fragmented landscape using 7.7 yr (1984-1992) of mark-recapture data. The study area included three kinds of 0.5-ha blocks: single large patches (5000 m²), clusters of medium patches (288 m²), and clusters of small patches (32 m²). We tested three predictions regarding animal movements. First, animal should move longer distances as fragmentation increases. Second, the proportion of animals moving will decrease as fragmentation increases. Third, species will show more movement from putative sources to putative sinks. In support of our first two predictions, all species (except male cotton rats) moved farther, and lower proportions of animals moved, as fragmentation increased. In testing our third prediction, we found no trends, for all species, between patch size and the net number of animals a block either imported or exported, indicating source-sink dynamics were probably not occurring on our study site. Furthermore, animals of all species (except female deer mice) switched more frequently to blocks of larger patches. For prairie voles in the spring and deer mice in the summer, relative abundance among blocks predicted from a Markov matrix model of switching probabilities showed high congruence with the actual abundances, indicating movement and abundance were related. In both cotton rats and prairie voles but not in deer mice, more juveniles and nonreproductive animals switched between blocks than did adults or reproductive animals. Deer mice switched more frequently than did either cotton rats or prairie voles; the latter species switched in similar frequencies. We discuss the implications of our data for modeling and conservation.
sábado, 2 de junho de 2012
Variation in size of colony of Molossus molossus and Molossus rufus in Rio de Janeiro state, Southeastern Brazil
ESBÉRARD, C.E.D. 2011. Variation in size of colony of Molossus molossus and Molossus rufus in Rio de Janeiro state, Southeastern Brazil. Neotropical Biology and Conservation 6(2):71-77.
Abstract. In the Neotropical region, knowledge of seasonal variation of bat colonies is low and appears to be fundamental to the choice of methods for estimating the total number of animals and husbandry. It was analyzed the monthly variations in the size of four colonies, two of Molossus molossus and two of Molossus rufus in Rio de Janeiro State, southeastern Brazil. A total of 60 nights of data collection was conducted in these four colonies, totaling 634 hours of work. The number of animals that comprised each colony was high, 293 and 474 in M. molossus and 165 and 363 in M. rufus. There are two types of colonies: reproductive, when it is observed increase in the number of animals during the months of reproductive activity, and not reproductive, when the colony size is larger in the months of inactive reproduction of the specie in this latitude and few bats remain in the refuge from October to February.
Abstract. In the Neotropical region, knowledge of seasonal variation of bat colonies is low and appears to be fundamental to the choice of methods for estimating the total number of animals and husbandry. It was analyzed the monthly variations in the size of four colonies, two of Molossus molossus and two of Molossus rufus in Rio de Janeiro State, southeastern Brazil. A total of 60 nights of data collection was conducted in these four colonies, totaling 634 hours of work. The number of animals that comprised each colony was high, 293 and 474 in M. molossus and 165 and 363 in M. rufus. There are two types of colonies: reproductive, when it is observed increase in the number of animals during the months of reproductive activity, and not reproductive, when the colony size is larger in the months of inactive reproduction of the specie in this latitude and few bats remain in the refuge from October to February.
quinta-feira, 31 de maio de 2012
XXV Jornadas Argentinas de Mastozoología
A Sociedade Argentina para o Estudo de Mamíferos (SAREM) e a Rede Latinoamericana de Mastozoologia (RELAM) convidam todos a participar das XXV Jornadas Argentinas de Mastozoología, e o II Congreso Latinoamericano de Mastozoología. Os eventos ocorrerão simultaneamente em Buenos Aires, Argentina, entre os dias 6 e 9 de novembro de 2012. Maiores informações no site do evento: http://sarem2012.com.ar/.
segunda-feira, 28 de maio de 2012
III Congreso de la Sociedad Peruana de Mastozoología
A Sociedade Peruana de Mastozoologia, o Instituto de Paleontologia da Universidade Nacional de Piura, e a Comissão Organizadora convidem todos os interessados a participar do III Congreso de la Sociedad Peruana de Mastozoología. O evento ocorrerá em Piura, no Perú, entre os dias 07 e 11 de outubro de 2012. As inscrições estão abertas pelo e-mail iiicongresospm@yahoo.com. Para maiores informações (incluindo custos) faça download da Primeira Circular.
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