Evolution and Origins - Unit 3: Species and Speciation

a group of organisms that share common characteristics and are distinct from other such groups. 

What is the general definition of a species?

a population (or group of populations) that interbreeds naturally and is reproductively isolated; shares consistent physical traits that distinguish it, and/or forms a distinct evolutionary lineage with a unique history. 

What is the combined definition of a species?

a species is a group of actually or potentially interbreeding natural populations whose members can produce viable, fertile offspring, and is reproductively isolated from other such groups. The key aspect is reproductive isolation. 

What is a species according to the biological species concept?

a species is a set of individuals with morphological features in common. The key aspect is the morphology of the members of a species. Individuals of a species are morphologically similar to one another, yet morphologically distinct from individuals from another species. 

What is a species according to the typological species concept?

A species may be defined by its unique genetic history as a tip of a phylogenetic tree. Species are defined by their unique derived features and shared ancestry. 

What is a species according to the phylogenetic species concept?

initiated by a geographic barrier between individuals from two natural populations. Physical separation of two populations = interruption of gene flow 

What is allopatric speciation?

takes place in a single geographic area so there is no geographic barrier to gene flow. May be prevented by polyploidy (especially in plants) or by habitat specialization. 

What is sympatric speciation?

speciation that occurs when populations are adjacent to each other – they live in neighboring areas with a narrow contact zone, but don’t mix freely. Populations share a border and are not completely isolated. 

What is parapatric speciation?

founder effect speciation; speciation that occurs when a small population becomes isolated at the edge (periphery) of a lagrer population’s range. A small group breaks away and is isolated with a small gene pool which leads to fast “evolution” 

what is peripatric speciation?

genetic divergence

the accumulation of genetic differences between two populations. 

• Founder effect 

• Mutation 

• Genetic Drift 

• Differential selection 

• Reproductive isolation

What are factors that are known to cause genetic divergence

prevents two individuals from distinct species from interbreeding to produce viable and fertile hybrid offspring. 

What is reproductive isolation?

prezygotic mechanisms

prevent mating or fertilization

postzygotic mechanisms

prevent zygote development or reproduction 

• Habitat isolation 

• Behavioral isolation 

• Temporal isolation  

• Mechanical isolation 

• Gametic isolation

What are some prezygotic mechanisms?

• Reduced hybrid viability 

• Reduced hybrid fertility 

• Hybrid breakdown 

What are some postzygotic mechanisms?

• Individuals can hybridize readily – no speciation 

• Individuals do not hybridize at all – full speciation 

• Individuals hybridize but offspring have reduced fitness – speciation in progress. Selection for strong reproductive barriers 

• Individuals can hybridize – increase adaptability by increasing variability in genome; increase possibility of speciation 

What are four possible outcomes with renewed or continued contact between two populations?

true

T/F Speciation and sexual selection usually depends on male attractiveness and female choosiness. 

Allopatry m=0; parapatry 0<m>0.5; and sympatry m=0.5 

When gene flow is “m,” and m=0 means no gene flow; m=1 means complete gene flow, what are the speciation rates of allopatry, paraptry, and sympatry? 

speciation

accounts for diversity of organisms 

Earth is less than 10k years old, and a worldwide flood eliminated all land animals except those on the ark 4k to 7k years ago. The diversity of life today is enormous with ~10,000,000 species and 75% being land species (majority = insects and microbes). Since there were only about 1,500 different kinds of land animals on the ark, some form of hyper-speciation would take place to get to what we have today. 

What is at stake for creation and speciation?

• After the flood, there were limited amounts of species, so natural selection and genetic drift would play a major role in speciation after the flood. Speciation would rapidly take place. 

• God created the “kinds” with genetic diversity, not as clones, so variation potential must be high. 

Why is speciation necessary from a creation perspective?

A population’s adaptation to 

• Environment 

• Food resources 

• Enemies 

• friends

What are aspects of coadaptation

Specific coevolution

Guild coevolution (diffuse coevolution)

Escape-and-radiate coevolution

Predator-prey coevolution

What are the different concepts of coadaptations?

specific coevolution

two species adapt in response to each other (co-speciation) 

guild (diffuse) coevolution

several species adapting to one another or one species adapting to several similar species 

escape-and-radiate coevolution

after an adaptive defense one species rapidly proliferates into a diverse grouping 

predator-prey coevolution

an unending arms race typically hits a stable equilibrium. Can involve continual cycles and sometimes result in the extinction of a species (pred or prey) 

adaptive radiation

adaptations in response to competition 

they result in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits with which they can exploit a range of divergent environments. 

What are the results of competitive interactions?

Intraspecific: competition that occurs within the same species 

• Can lead to natural selection, as only individuals best adapted to limited resources survive and reproduce. Helps regulate population size. 

• Involves same species with complete resource overlap 

What is intraspecific competition?

Interspecific competition: competition that occurs between species 

• Can result in competitive exclusion (one species out-competes and eliminates the other) or niche partitioning (species evolve to use different resources or occupy slightly different niches) Influences community structure and biodiversity. 

• Involves different species, partial resource overlap. 

What is interspecific competition?

Dangerous, but not lethal. Learning of predators is important and if lethal, no memory.

What is the main idea behind aposematism and mimicry?

batesian mimicry

when a harmless species (mimic) evovles to imitate the warning singles of a harmful or unpalatable (model) species to avoid predators. The mimic is a faker – it gains protection without actually being dangerous. 

Mullerian mimicry

When two or more harmful or unpalatable species evolve to resemble each other, reinforcing the predator’s learned avoidance. Everyone’s dangerous—so predators learn faster and avoid all look-alikes. 

symbiosis

any two organisms living in close association, commonly one living in or on the body of the other, are symbiotic, as contrasted with free living. 

• Mutualism: (+/+) both benefit 

• Commensalism: (+/0) one benefits while the other is neither harmed/benefited. 

• Parasitism: (+/-) one benefits while the other is harmed 

What is the difference between mutualism, commensalism, and parasitism?

Two or more competing species that use the same resource cannot coexist indefinitely. Leads to extinction and/or character displacement. 

What is the competitive exclusion principle?

• When a species expands its niche (uses more resources or occupies a wider range of habitats) after competitors are removed or reduced. 

• Usually occurs when a species colonizes a new area with few competitors or predators and when competing species go extinct or leave the area. 

• Leads to broader resource use or population increase.

What is ecological release?

• When two similar species living in the same area (sympatric) evolve different traits (like beak size, feeding behavior) to reduce competition. Happens due to interspecific competition – when overlapping niches create selective pressure for differences. 

• Leads to niche differentiation and enhances coexistence by minimizing direct competition.

What is character displacement?

The theory that all organisms on Earth are related by common ancestry and that they have changed over time, predominantly via natural selection 

Definition of evolution

“Any consistent difference in fitness among phenotypically different classes of biological entities.” Acts on individuals to alter the variation in a population. 

Definition of natural selection

The transfer of genetic material (alleles) from one population to another of the same species through movement and breeding of individuals (or their gametes, like pollen or sperm). How genes move between populations. 

What is gene flow?