137 research outputs found
Gause's exclusion principle revisited: artificial modified species and competition
Gause's principle of competition between two species is studied when one of
them is sterile. We study the condition for total extinction in the niche,
namely, when the sterile population exterminates the native one by an optimal
use of resources. A mathematical Lotka-Volterra non linear model of interaction
between a native and sterile species is proposed. The condition for total
extinction is related to the initial number of sterile individuals
released in the niche. In fact, the existence of a critical sterile-population
value is conjectured from numerical analysis and an analytical
estimation is found. When spatial diffusion (migration) is considered a
critical size territory is found and, for small territory, total extinction
exist in any case. This work is motived by the extermination agriculture
problem of fruit flies in our region.Comment: 11 pages. Published in Jour.Phys.A Math.Gen. 33, 4877 (2000
Tree thinking cannot taken for granted: challenges for teaching phylogenetics
Tree thinking is an integral part of modern evolutionary biology, and a necessary precondition for phylogenetics and comparative analyses. Tree thinking has during the 20th century largely replaced group thinking, developmental thinking and anthropocentricism in biology. Unfortunately, however, this does not imply that tree thinking can be taken for granted. The findings reported here indicate that tree thinking is very much an acquired ability which needs extensive training. I tested a sample of undergraduate and graduate students of biology by means of questionnaires. Not a single student was able to correctly interpret a simple tree drawing. Several other findings demonstrate that tree thinking is virtually absent in students unless they are explicitly taught how to read evolutionary trees. Possible causes and implications of this mental bias are discussed. It seems that biological textbooks can be an important source of confusion for students. While group and developmental thinking have disappeared from most textual representations of evolution, they have survived in the evolutionary tree drawings of many textbooks. It is quite common for students to encounter anthropocentric trees and even trees containing stem groups and paraphyla. While these biases originate from the unconscious philosophical assumptions made by authors, the findings suggest that presenting unbiased evolutionary trees in biological publications is not merely a philosophical virtue but has also clear practical implications
ESTROGENS IN MARINE INVERTEBRATES
Volume: 112Start Page: 180End Page: 18
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