SEXUAL SELECTION Sexual Selection Form of selection that promotes traits that increase an individual's access to reproductive opportunities Intrasexual Selection Form of sexual selection involving interactions between individuals of 1 sex; competition within 1 sex for access to the other e.g .: Physical size (large horns, large size), fighting ability Intersexual Selection Form of sexual selection involving interaction between males and females; as when one sex chooses from another e.g .: Colourful feathers THE BIOLOGICAL SPECIES CONCEPT (BSC) Species A group of individuals that can exchange genetic material through interbreeding to produce fertile offspring BSC A group of actually or potentially interbreeding populations that are reproductively isolated from other such groups Partially Reproductively Isolated Populations that have not yet diverged as separate species but whose genetic differences are extensive enough that the hybrid offspring they produce have reduced fertility or viability compared with offspring produced by crosses between individuals within each population THE BSC IN THEORY Morphospecies Concept Idea that members of the same species usually look like each other more than like other species ISSUE #1 . Need to test whether 2 individuals can produce fertile offspring - but conditions (e.g .: time constraints) will not allow them to reproduce/behave in a natural way · Morphospecies concept is therefore used · However, species may have different phenotypes - called polymorphisms ISSUE #2 · The BSC cannot apply to species that reproduce asexually (e.g .: bacteria) ISSUE #3 . The BSC cannot apply to species that are extinct as they are only known through fossil record (e.g .: dinosaurs) RING SPECIES & HYBRIDISATION Ring Species Species that contain populations that are reproductively isolated from each other but can exchange genetic material through other linking populations · Ring species presents another issue with the BSC · Some populations within a species are reproductively isolated from each other - but others are not Hybridisation Interbreeding between 2 different varieties or species
· Different species of willow are capable of exchanging genes with other species in their genera through hybridisation . According to the BSC, they should be considered as one large species . However, they maintain their distinct appearances and natural selection must work against the hybrid offspring ECOLOGY, EVOLUTION & THE BSC Different concepts have been brought forth to modify & improve the BSC ... Ecological Niche A complete description of the role a species plays in its environment . It is impossible for 2 species to co-exist in the same location if their niches are too similar . Competition between them for resources will lead to the extinction of one of the species Ecological Species Concept (ESC) Idea that these is a 1-to-1 correspondence between a species and its niche · Can determine whether or not certain lineages are distinct species based on the differences or similarities in their ecological requirements · If 2 lineages have very different nutritional needs, we can infer on ecological grounds that they are separate species Phylogenetic Species Concept (PSC) Idea that members of a