No abstract

Variable bandwidth kernel density estimators increase the window width at low densities and decrease it where data concentrate. This represents an improvement over the fixed bandwidth kernel density estimators. In this article, we explore the use of one implementation of a variable kernel estimator in conjunction with several rules and procedures for bandwidth selection applied to several real datasets. The considered examples permit us to state that when working with tens or a few hundreds of data observations, least-squares cross-validation bandwidth rarely produces useful estimates; with thousands of observations, this problem can be surpassed. Optimal bandwidth and biased cross-validation (BCV), in general, oversmooth multimodal densities. The Sheather-Jones plug-in rule produced bandwidths that behave slightly better in this respect. The Silverman test is considered as a very sophisticated and safe procedure to estimate the number of modes in univariate distributions; however, similar results could be obtained with the Sheather-Jones rule, but at a much lower computational cost. As expected, the variable bandwidth kernel density estimates showed fewer modes than those chosen by the Silverman test, especially those distributions in which multimodality was caused by several noisy minor modes. More research on the subject is needed.

Abstract:The reproductive season of tilapia was studied by monthly samplings at Emiliano Zapata dam, Morelos State, Mexico. From February 1999 through February 2000 a sample of 50 fish was taken from the commercial catch (castnet, 6.5 cm of mesh size). The observed sex ratio was 1:1.29 (females:males) (χ²=10.26; p<0.05). The tilapia reached maturity at 151.3 mm (females) and 152.0 mm (males) of total length. Rainy (August) and dry (February) seasons were determined as the breeding period. Fecundity variation was better correlated with length (r=0.7473; p<0.002) than with weight (r=0.7395; p<0.002). The fecundity ranged between 243 and 847 oocytes per fish, with egg diameter from 300 to 3 700 µm. Intensive breeding activity in August and February coincide with phytoplankton biomass increase. Rev. Biol. Trop. 53(3-4): 515-522. Epub 2005 Oct 3.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Society for the Study of Amphibians and Reptiles is collaborating with JSTOR to digitize, preserve and extend access to Journal of Herpetology.ABSTRACT.-The reproductive cycle and diet of a population of the viviparous lizard Sceloporus torquatus torquatus from the Pedregal de San Angel, Distrito Federal, Mexico, were studied. Ovarian activity began in June, and by October, one to five preovulatory follicles per ovary were present Ovulation took place in November and December, and parturition occurred in late April or early May. Relative litter and egg masses were higher at the end of development than at the beginning. Testes increased in size from June through September, when they reached their maximum volume and weight Testicular regression began at this point and was particularly accentuated in October and November. The diet of both sexes was composed primarily of insects; however, plant material (small flowers and fruits), spiders, isopods, and occasionally earthworms were also consumed. Both sexes consumed plant material throughout the year. In the dry season, males ingested twice as much food as females.

Age and growth of Nile tilapia (Oreochromis niloticus) were determined using 1 039 specimens collected in a tropical shallow lake of Mexico, from January to December 1993. Standard length of females ranged from 9.0 to 16.5 cm and males from 8.9 to 14.8 cm. The standard length-weight relationships for all individuals was BW=0.1207 SL 2.469 . The age data, derived from opercular bone readings, were used to estimate the growth parameters of the von Bertalanffy equation: L ∞ =17.88 cm, K=0.3409, t o =-1.543, and W ∞ =149.21 g. The oldest male and female were 2.5 years old. The sex ratio (female:male) was of 1:1 (χ²=0.02, p>0.05). Rev. Biol. Trop. 56 (2): 875-884. Epub 2008 June 30.