| Abstrakt: |
Populations ofLittorina mariae, L. obtusata andL. saxatilis from the coast near Roscoff (Brittany), from the North Sea islands Helgoland and Sylt were investigated with regard to several characters of their reproductive biology. Important factors are body size and weight, maturation size, shell thickness, sex ratio and reproductive effort of adults as well as number, size and mortality of embryos. MatureL. saxatilis individuals inhabiting sandy shores are smaller and have thinner shells and higher reproductive effort than those on rocky coasts. On shores with loose and semipermanent boulders the adults are clearly larger. Interannual variations in some life history parameters may be explained by changes in food supply. In populations with small adults, ♀ ♀ are bigger than ♂ ♂. In localities whereL. mariae andL. obtusata occur sympatrically, a tendency to accentuate interspecific contrast is recognized. Life history patterns, especially inL. saxatilis populations, show two tendencies: (a) a rapid increase of shell-size and thickness, which offers better chances of survival and of maximizing clutch-size and clutch-numbers during life-time; (b) early entrance into maturity leads to accelerated reproduction, but life expectation is reduced. Both tendencies are balanced by the action of biotic and abiotic factors. |
Full text from SpringerLink