Dynamique des populations pdf

Spatial variation in recruitment. Over the l OO -km extent of our stud y area, we observed substantial spatial variation in recruitment. Such variation is not surprising as the recruitment of invertebrates with planktotrophi c life cyc les is notori ously variable in marine systems Harris et al. Although substantial vari ation was observed at aIl three scales, there was only signiftcant variation at the smallest sca le, i.

It is likevvise surprising that there was no correlation between recruitment in subtidal habitats and recruitment in intertidal habitats. Given the proximity of the two habitats at a given site usuall y less than 1 km relative to the km separation of the sites, one would expect both habitats to have a similar exposure to potential recruits i.

Perhaps the lack of any patterns was due to the general lack of signift cant variation at this spatial scale see above , but this result suggests that one cannot sim ply assume that different habitats that are in close proximity will have similar conditions. For example, bottom topography might interact with coastal currents to alter the flow of water across the bottom. The lack of any correlation between the abundance of adults and recruits in intertidal environments is also surprising in certain senses.

Given the wide dispersa l of musse l larvae during their planktonic period, no relationship between adults and recruits would be expected in terms of local reproduction i. Brock, V. Ophelia 17 , — Castel, J. Keegan, P. Ceidigh and P. Oxford: Pergamon Press. Guelorget, O. Hasselblad, V. Technometrics 8 , — Meddr Danm. Jelnes, J. Russell: Isoenzyme taxonomy applied to four species of Cardium from Danish and British waters, with a short description of the distribution of the species Bivalvia.

Ophelia 9 , 15—19 Koulman, J. The Cardiidae. Basteria 41 , 21—32 Labourg, P. Colloque «Ecotron», Brest, 3—6 juillet Publs Cent. Colloques 7 , — Levinton, J. Mars, P.

Vie Milieu Suppl. Muus, B. Distribution and ecology of dominating species in the shallow reaches of the mesohaline zone. Except for this, the combined effect of migration and natural enemies were allowed to maintain aphid population at acceptable level.

The regulatory action of these factors has been analysed and discussed. Bien que la sbve, base d e leur alimentation, soit de 1, 2,. JRAD et D. Jerraya 3 RCsultats prcssion de facteurs physiques et biotiqiics mais elks 3. Pour cela 3. Tout se passe donc comme si, avec les generations hCtCrogCneitC de la contamination. La fig. La consequence en est vraisemblablement une 3. On en dkduit que le puceron est capable de H. Jun Jun Fig. Sur amandier, le puceron peut ttre attire plus par La reduction de la fecondite ne constitue pas la seule une variete que par une autre.

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Cette periode se situe de novembre a fin nomique. Comparke a celle prbente avant dkbourrement potentiel biotique des femelles vivipares aptkres. Tableau 3. Evolution de la ponte sur amandier var. Celles-ci, metrie. Dans ce cas toute la sur- par la suite une allure exponentielle, culminant a la face foliaire est couverte de pucerons se presentant en mi-avril. Inversement en annCe insuffisam- 4. A ces varia- sentir sur la vegetation avec pour consequence des tions pluviomktriques qui sont la regle en regions mCdi- pousses assez developpees.