Robert Barbault

DENSITY DEPENDENCE IN THE COMMON LIZARD: DEMOGRAPHIC CONSEQUENCES OF A DENSITY MANIPULATION'

Density dependence plays an important role in the regulation of most pop- ulations. Descriptive studies provide only limited evidence, while density manipulations are thought to be a more powerful tool. Here, we describe such a manipulation. We experimentally analyzed demographic responses to changes in density in common lizard (Lacerta vivipara) populations. Two neighboring sites were studied from 1986 to 1988. At the end of the first year, density was artificially decreased at one site and increased at the other. The evolution of demographic parameters over time (before and after ma- nipulation) was compared between the two sites. We found that: (1) density in each age and sex class quickly converged to pre-experimental values at both sites; (2) survival rates (introduced individuals excluded) were unchanged, except that juvenile mortality was pos- itively related to density; (3) emigration rates remained low and did not seem to be influ- enced by density, while immigration rates were negatively influenced by density; (4) the proportion of young reproductive females was negatively influenced by density; (5) body length and growth rate were negatively influenced by density only in yearlings, and at least in females, no catchup on growth is apparently possible; no difference in reserve storage was found; and (6) female reproduction was modified by the manipulation through clutch size and hatching success, which were negatively influenced by density; however, no dif- ference was detected for hatching date, number of abortive (clear) eggs, prenatal mortality, reproductive investment, and body mass of live neonates. Rapid density readjustments were mostly explained by immigration into the site where density was decreased, and by high mortality of introduced individuals and of native juveniles where density was increased. Other parameters that were influenced by the ma- nipulation could only have induced delayed effects on population density. Different age and sex classes showed different responses to density. These responses indicate that density dependence plays a key role in shaping the demography of this lizard species.

Incumbent Advantage in Common Lizards and their Colonizing Ability

Settlement in a new environment is a key phase in effective dispersal. We investigated this phase in the common lizard (Lacerta vivipara Jacquin) by an experimental introduction of known individuals. Introducing lizards in an already occupied environment revealed a prior-residence advantage and some differences in the ability of individuals to face a new environment under conditions of high intraspecific competition. Transplanted individuals (TI) died in larger numbers than resident ones (RI) immediately after the introduction, except for juveniles. This prior-residence advantage could arise from the difference of familiarity with the local environment or from a dominant behaviour of RI on TI

THE EVOLUTION OF OVIPARITY WITH EGG GUARDING AND VIVIPARITY IN LIZARDS AND SNAKES: A PHYLOGENETIC ANALYSIS

This paper investigates the evolution of viviparity and of egg guarding in lizards and snakes in which three modes of reproduction can be described: oviparity without egg guarding, oviparity with egg guarding, and viviparity. All possible transitions of reproductive modes were detected in each taxon using Maddisons method. We then tested two specific hypotheses. First, egg guarding can be regarded as an alternative to viviparity. A relatively frequent association of egg guarding and viviparous species in the same taxon may be due to similar environmental conditions or species characteristics leading to two different solutions. Second, egg guarding may facilitate the evolution of viviparity. This hypothesis is supported by the high frequency of viviparous species in taxa containing egg guarding species and by a tendency for prolonged uterine retention of eggs in brooding squamates. Our analyses demonstrate that the first hypothesis is the best supported. Egg guarding and viviparity most often evolved independently. If a major benefit of egg guarding is the repulsion of potential predators, size is one of the most obvious morphological characters that should be correlated with the evolution of reproductive modes. The two reproductive traits were correlated to a reduction in body size for viviparous species and an increase in body size for egg guarding species. This could partly explain why the evolution of these reproductive modes seems almost antagonist.

Spatial and behavioural consequences of a density manipulation in the common lizard1

AbstractDensity has been assumed to be a determinant factor of population regulation in the common lizard (Lacerta vivipara), as in most reptiles. This assumption was tested by experimentally decreasing and increasing the density of two wild populations from Mont Lozere (Massif Central, France). The behavioural modifications induced by the experiment are reported here. Spacing behaviour, habitat use, level of aggression and level of activity were studied in both populations during two to three years following the manipulation. The density manipulation affected all the variables studied, but most of the differences due to the site vanished two years after the beginning of the experiment. Space use (home range size and co-occurrence) and time of activity were deeply modified, most probably because of an increase of competition level. According to their age and sex, individuals reacted differently. On the site with increased density, yearlings were more often excluded from the potential foraging sites and th...

La vie, un succès durable

Abstract As one of the few scientific disciplines facing the challenge of sustainable development, ecology is in a privileged position for addressing sustainability issues. In this perspective, life can be viewed as the paradigm of sustainable development: a success story lasting four billion years. Such a reflection leads us to rethink the meaning of ecology. Thus, we consider successively the way in which life addresses its hidden face concerning human sciences; how it tackles the debate on sustainable development; and we question its approaches to biological conservation. Such a reflection also results in a more general conclusion: the ultimate condition for a sustainable development of scientific research itself, ecological or not, will depend on our taking into account the point of view of our society.

Reply from F. Sarrazin and R. Barbault

Bullock and Hodder underline two llmitatlons affecting the involvement of scientists wrth reintroduction programmes: (I) iimlted fundmg for basic research. and (2) the misuse of eeneral concepts in reintrodtdction planning.

Man and Biodiversity

Although the word was coined in 1985, the concept of biodiversity really emerged in Rio de Janeiro in June 1992 with the global media coverage it received during the United Nations Conference on Environment and Development. It is therefore, not a uniquely biological concept. Over and above simple considerations on the diversity of the living world — the state and dynamics of genetic variability, the richness of flora and fauna, the diversity of ecosystems — biodiversity really refers to mankind: mankind who threatens it, mankind who depends on it for his needs and well-being, mankind as a species, and mankind as the species to be held responsible for it.