Drake University Bio 13 Exam 2

• Mechanisms causing divergence

  • Selection

  • Non-random mating

  • Mutation

  • Genetic drift

  • Migration does not cause divergence

• Biological species concept (BSC)

  • Reproductive isolation

• Phylogenetic species concept (PSC)

  • Identify the smallest diagnosible monophyletic group

  • More useful and practical apparently

• Both agree

  • Both agree on independent evolutionary units

  • Agree that evolutionary units lack gene flow

• Disagree about the criteria used to determine when a lack of gene flow has happened

02/24/25

• Speciation

  • 1. Interrupt gene flow (migration)

    • Physical isolation (allopatric model)

      • Dispersal

        • getting past or going over a barrier

      • Vicariance (splitting)

        • A new barrier splits a current population

          • Glaciers, road construction

      • Sympatric model

        • Strong selection

        • Animals have a preference for extreme characteristics and ignore mates that don’t have this characteristic which can quickly drive a population to diverge

  • Reinforce speciation

    • Ignore

    • Behavioral isolation

    • Temporal

    • Habitat

    • Mechanical

    • Gametic (their gametes aren’t compatible)

  • 2. Divergence

    • Mutation

    • Selection

    • Genetic drift

    • Non-random mating

• Ecology

  • The study of species and species’ interactions with one another in their environment

  • Niche

    • Abiotic factors → combine to create a climate

      • Temperature

      • Water

      • Amount of sunlight

      • Wind

      • Soil

    • Biotic factors

02/26/25

• Niche

  • Abiotic factors

  • Biotic factors

    • We can study niches in a more mathematical way by plotting them on a graph with the axes representing different variables

  • Competitive exclusion hypothesis

    • Two species cannot occupy the exact same niche in the exact same location, because then they would be in direct competition for the exact same set of resources

    • Partition of resources

    • Character displacement

      • Humans exterpated wolves from the United States and they eventually spread back into their niche after humans stopped interfering

02/28/25

• Patters that drive community richness (diversity)

  • Island-equilibrium model

    • If the island is bigger, it should have more species on it

    • If two islands are the same size, the one that is closer to the mainland should have more species because animals can get there from the mainland more easily

    • As you remove islands you lose species because they can’t go somewhere else where their niche is already filled

    • Inter-specific species interactions

      • Predation (+/-)

        • One species eating another species

        • Causes co-evolution because each species is trying to outcompete the other

        • “Arms race”

        • Predator/prey: weapons → specialized structures, camouflage, strength, size, speed, intelligence, agility, endurance, social/solitary

      • Mutualism (+/+)

        • Both species are benefitting from the interactions

          • Oxpeckers, cleaner wray

      • parasitism/disease (+/-)

        • Parasitism: larger organisms that need boats (ticks, tapeworms)

        • Disease: smaller (parasites, bacteria)

        • Strengthens immune system, increases defensive mechanisms

        • Diseases and parasites evolve to avoid detection and avoid harming the host too much so as not to kill them

      • Commensalism (+/0)

        • One species benefits, the other is neutral

        • Not a very common species relationship

      • Herbivory (+/-)

        • Plants develop things like bigger size, spiny structures, and toxins

        • Animals develop the ability to eat them regardless

    • Trophic levels – trophic cascade!

      • Energy is lost as you go up the food chain

      • Dominant species is the most abundant species in the food web/chain

03/03/25

• Dominant species

  • Very large biomass

  • Bottom-up control

• Keystone species

  • Pivotal role in the community

  • Top-down control

  • Otters eat sea urchins so the kelp forests can grow

• Population ecology

  • Intra-specific

    • ∆N/∆T

      • dN/dT

      • Change in population in an interval of time

      • N = population size, T = time

      • dN/dT = r(N)

        • r = per capita rate of increase

        • d = per capita death rate

      • Ex: b = 10/100 = 0.1

      • Exponential growth curve, the population grows faster as time passes

03/10/25

• Our relative abundance changes which impacts the resource availability for other species

  • ~ 10,000 species of birds

    • ~ 130 have gone extinct

    • ~1% gone in 400 years

    • Maybe 100% gone in 40,000 years

• Mass extinction – 60% of species in 1 million years