Natural selection can alter the distribution of traits, depending on which phenotypes are favored. Will always favor those traits with the highest reproductive success directional selection conditions favor individuals exhibiting one phenotypic extreme occurs in environmental changes disruptive selection conditions favor individuals at both phenotypic extremes stabilizing selection acts against both extreme phenotypes, favors intermediate variants reduces variation of a particular trait

Sexual Selection individuals with certain characteristics are more likely to obtain mates result in sexual dimorphism (differences between males and females) often result in extreme ornamentation or behavioral displays in males, driven by female selection of mates (choosy females) the benefit must outweigh the risk (benefit of passing on genes outweighs attracting predators with bright colors/displays) birds (peacock) may result in competition among males for access to females Ungulate rutting

Speciation process by which one species splits into two or more species explains similarities and differences among organisms (common ancestry) macroevolution: development of new groups of species Birds, mammals, flowering plants

Species-Concepts (definitions) Biological species concept a species is a group of populations whose members have the potential to interbreed in nature and produce viable fertile offspring “reproductively compatible” emphasizes gene flow between populations morphological species concept characterizes a species by body shape and other structural features subjective ecological species concept views a species in terms of its ecological niche emphasizes adaptation to environments phylogenetic species concept smallest group of individuals that share a common ancestor

Reproductive Isolation existence of biological factors (barriers) that impede members of two species from interbreeding and producing viable, fertile offspring zygote = fertilized egg prezygotic barriers block fertilization from occurring by: impeding mating preventing mating from being completed successfully hindering fertilization postzygotic barriers developmental errors lead to reduced survival of embryo hybrids infertile, or don’t live long enough to reproduce Zonkeys and Ligers! FIGURE 24.3

How new species arise... Allopatric Speciation gene flow interrupted by geographic barrier geographic barrier is different for each population Once gene pools have diverged, mutations arise and natural selection alters gene frequencies this leads to reproductive isolation over time evidence that speciation has occurred... two populations brought back together and unable to reproduce, or prefer members of their own population

Sympatric Speciation occurs in species that live in the same geographic area (less common) caused by: polyploidy (extra chromosomes--mistakes in cell division) habitats (exploit habitat/resource not used by parent population) sexual selection

Extinction Majority of organisms that ever lived are now extinct 5 historical mass extinctions Permian Largest extinction event…90% of species extinct Effected mostly marine life. Recovery took ~30 million years. Triassic-Jurassic 70% of species extinct. Dinosaurs evolved. Cretaceous (K-T extinction) resulted from volcanic eruptions and a warming atmosphere 75% of species extinct. Mammals and Birds evolved as a result. Are we in a current 6th mass extinction?? Extinction rate is estimated 100-1000x higher than background rate (yikes!)

Consequences of Extinctions decrease ecosystem biodiversity drastically millions of years for species to rebound adaptive radiation: period of evolutionary change when groups of organisms form many new species as a result of their adaptations to fill vacant niches in an ecosystem have occurred after all major extinctions “Cambrian explosion”—530 million years ago, huge increase in animal life. change ecosystem dynamics (disrupt balance in species interactions)

Evolution-Behavior Connections Parental Care Maximize reproductive success by caring for offspring Maximize reproductive success by mating with several females…letting the females care for offspring Brood Parasites Certain species will lay their eggs in the nest of another and leave them to raise their young Altruism Reduces an individuals fitness, but increases the fitness of other individuals in the population Kin selection: favors altruistic behavior by enhancing reproductive success of relatives Bees, many rodents, elephants, chimpanzees… Mate Choice/Sexual Dimorphism Promiscuous (males showier)/monogamous (less differences between sexes) Sneaky Males Smaller males that sneak in to mate or fertilize eggs of the female Some actually mimic females

Foraging Behavior Agnostic Behavior Mimicry Plant defenses Natural selection favors behaviors that enhance efficiency of feeding (search, recognize, capture food) Agnostic Behavior Competition that results in access to a resource (food, mates) Mimicry Cryptic coloration (camouflage) Aposematic coloration (warning coloration) Across species, similar colors are used as warning (convergent evolution) Batesian mimicry (harmless species mimics harmful one) Mullerian mimicry (two unpalatable species mimic each other) Plant defenses Thorns, toxins, attracting other predatory animals to feed on herbivores White-striped clover!