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Chapter 19

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Tristan Long

Chapter 19: Species 19.1 What’s in a name? ● Communication can affect both interspecific and intraspecific behaviours ● Biologists use scientific names, Latinized descriptions of the organism bearing the name, each described species has a scientific name 19.2 Definition of Species ● Species are the fundamental taxonomic units of biological classification ● The Biological Species Concept defines a species as a group of organisms that can successfully interbreed and produce fertile offspring ● The Phylogenetic Species Concept defines a species as a group of organisms bound by a unique ancestry ● The Ecological Species Concept defines a species as a group of organisms bound by a unique that share a distinct ecological niche ● These definitions do not work well with species that reproduce asexually ● Androdioecy and gynogenetic species are variations in patterns in reproduction ● Androdioecious organisms exist as natural populations of functional males and hermaphrodites but include no ture females. ● Gynogenetic species have only females. Within these females, the eggs require mechanical stimulation by sperm to initiate development ● Hybridization is when two species interbreed and produce fertile offspring 19.3 One Size Does Not Fit All ● The biological species concept defines species in terms of population genetics and evolutionary theory in a static world ● The definition alludes to the cohesiveness of species ● The second part emphasizes the genetic distinctiveness of each species. because populations of different species are reproductively isolated, they cannot exchange genetic information ● Speciation is defined as the evolution of reproductive isolation between populations ● Biologists uses similarities or differences in morphological traits a convenient markers of genetic similarity or reproductive isolation ● Morphological species concept is the idea that all individuals of a species share measurable traits distinguish them from individuals of other species 19.4 Gene Flow ● Gene Flow occurs within populations of single species ● Ecology, habitat availability and behaviour affect distributions patterns and genetic differences ● Changes in landscape and habitat can alter genetic patterns. 19.5 Genetic Variation ● Subspecies are identified as geographically separated populations of a species exhibit dramatic, easily recognized phenotypic variation. ● Ring Species have ring shaped geographic distribution that surround uninhabitable terrain ● When a species is distributed over a large, geographically diverse area, some traits may exhibit a cline. ● A Cline is a pattern of smooth variation along the geographic gradient. Clinal variation usually results from gene flow between adjacent populations that are each adapting to slightly different conditions ● When Cline extends over a large geographic gradient, populations at the opposite end of the cline may be very different. 19.6 Reproductive Isolation ● Reproductive isolating mechanism is a biological characteristic that prevents the gene pools of two species from mixing even when they are sympatric ● Sympatric means occupying the same spaces at the same time ● Reproductive isolation can be achieved by either prezygotic isolating mechanisms exert their effects before the productions of a zygote or fertilized egg. The other way is postzygotic isolating mechanisms which operate after zygote formation ● Ecological isolation is when one species in the same geographic region experience isolation if they live in different habitats ● Temporal isolation occurs when species living in the same habitat can experience isolation if they mate at different times of the day or different times of the year ● Behavioural isolation results when the signals used by one species are not recognized by another. These signals may be so complicated that signals sent by one species are not recognized by another. ● The number of males with recognizable traits, as well as the number of females able to recognize the traits, increases in the population, driven by sexual selection ● Mechanical isolation results when differences in the structure of copulatory organs prevent successful mating between individuals of different species ● Gametic isolation is the incompatibility between the sperm of one species and the eggs of another ● Even when individuals of different species do mate, gametic isolation may prevent isolation ● When two species are reproductively isolated if their offspring, called interspecific hybrids, have lower fitness than those produced by intraspecific matings ● Three postzygotic isolating mechanisms can reduce the fitness of hybrid individuals ● Hybrid invalidity can occur because many genes govern complex process that transform a zygote into a mature organism. Hybrid organisms frequently die as embryos or at an early age. ● Hybrid sterility results when the parent species differ in the number or structure of their chromosomes, which cannot pair properly during meiosis. Such hybrids have zero fitness because they leave no descendants. ● Hybrid breakdown is the reduced survival or fertility between generations of hybrid mating ● Reproductive isolation is maintained between the species because of there is little long term mixing of their gene pools 19.7 Geography of Speciation ● Geography has a huge impact on whether gene pools have the opporuntity to mix ● The three modes of speciation based on geographic relationship of populations as they become reproductively isolated: allopatric speciation, parapatric speciation and sympatric speciation ● Allopatric speciation can occur when a physical barrier subdivides a large population or when a small population becomes separated from a species’ main geographic distribution. This occurs in two stages; First, the two populations become geographically separated preventing gene flow between them. Then as the populations experience distinct mutations as we
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