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What's the use of avoiding predators, obtaining nutrition, and surviving to adulthood if you don't mate successfully?
After mating, selective pressures don't mean much, which is why bodies begin to fail following reproductive age
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Two basic categories of reproduction
- Asexual-without sex
- Sexual
- Both achieves goal of increasing population size
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Asexual reproduction
- Mitotic division-single celled organisms(1 cell -->2 cells)
- Budding-corals&anemones(part of body falls off and regrows) can be sexual also
- Vegetative spreading-plants(grass sends runners underground) can be sexual also
- Fission-paratomy(zoids/rhizoids attached together or living as a colony) and architomy(part of body cut off and regenerated)
- Parthegenesis-some insects, minnows, and lizards(all individuals are females)
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What is male&female?
- Females produce larger, more energetically costly gametes
- Males produces smaller, less energetically costly gametes.
- Female reproduction is resource limited
- Male reproduction is limited by mate access
- Females allocate more resources per gamete than males
- Males have amplified differences
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Sex achieves two main goals
- Increase population size
- Create new genetic combinations(asexual doesn't do this)
- Sexual reproduction is found in 97% of animal species
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Evolutionary costly
- Cost of Meiosis(cost of males)-50% of genes only passed on
- Cost of recombination(outcrossing depression)-new genotype might be less fit, can also be better fit=superfit
- Cost of mating
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Costs of mating
- sexual mechanisms-grow flowers, pheromones, and sex organs
- cost of mating behavior-displays, more susceptible to enemies=bright colors
- Injury inflicted by male
- Disease transmission-pathogens being transferred=std's
- cost of escape from unwanted sexual attention-fleeing from a male you don't want to mate with
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Why have sex?
- Ultimate(ex. evolutionary) vs. proximate(ex. fun) reasons
- Red queen hypothesis-have to evolve to meet new challenges. most correct reason
- Slow reproducing organisms have sex the most
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Red Queen hypothesis
- pathogens are a very important selective force
- sex presents pathogens with a moving target making it difficult for them to evolve counter-adaptions to our defense mechanisms
- challenges pathogens bc of unique individuals
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Parental care
- main diff. between male and female is investment in gametes
- the one that abandons is the one that can't abandon last
- internal(mostly females, but not with seahorses) vs. external(female drops eggs, then male has to squirt to fertilize) fertilization
- nature is not moral, will abandon one young to raise another
- gaming theory- baby dies if no parents, but survives with one
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Who do you swap genes with when reproducing sexually?
- Someone w/ good genes
- W/ anybody you can find
- Sperm is cheap, mating isnt(intense competition for mates)
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How many mates?
- Monogamy-single mate
- Polygyny-multiple females, harems/territories, polygynous often have sexual dimorphisms
- Polyandry-multiple mates. leads to sperm competition and large testicles
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sexual selections
- differences in reproductive rates among individuals as a result of differences in mating success
- intrasexual selection-individuals of one sex compete among themselves for mates. male-male, harems
- intersexual selection-individuals of one sex consistently choose mates among members of opposite sex based on a particular trait. female choosiness.
- mechanism that drives evolution, also
- selective pressure-females selecting traits in males because they are choosier, traits get passed on to next generation
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Bright colored guppies and predation
- females prefer males with bright colors
- bright colors attract predators
- w/ predators in pool, not too successful in reproducing offspring with bright colors
- pool w/ more predators=dull colors
- pool w/ weak to no predators=bright colors
- same results in non-controlled experiments, colors depend on predators
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Scorpian-flys
- male scorpian fly makes a nuptial gift to attract females to mate.
- cost is availability of gift, usually food.
- females chose males with best offerings, medium&large crickets over no gift and saliva
- type of offering is related to dominance that is related to the size of the fly
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sexual dimorphism
- any consistent difference between males and females beyond the basic functional portions of the sex organs, antlers/genitalia don't count!
- larger harem=greater battles=greater sexual dimorphism
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sexual dimorphism in primates
- humans-intermediate, monogamous, no harems
- gorilla-polygynous, has harems
- chimp/bonobo-polygamous, polyandrous
- mate competition was greatest with polygynous primates, larger body size&larger canine size
- primates with the largest testicles had the greatest sperm competition
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what does intermediate sexual dimorphism and testicle size indicate about the evolution of human mating systems?
- suggests that we're between chimps and gorillas in terms of polyandry and polygyny
- our harems aren't as large as gorillas, not as promiscuous
- human females are less promiscuous than female chimps, but these traits aren't consistent with monogamy
- it has been suggested that sexual selection by females is responsible for male penis size-longest and thickest of any primate. and human brain size
- monogamy=human intelligence?
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Are humans monogamous?
- depends on culture
- males are generally more promiscuous than females
- humans are polygamous, also serial monogamy
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evolution of sociality is generally accompanied by
- cooperative feeding, defense of the social group, and restricted reproductive opportunities
- cooperation involves exchanges of resources or other forms of assistance
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eusociality
- more complex level of sociality
- three major characteristics:
- -individuals of more than one generation living together
- -cooperative care of young
- -division of individuals into non-reproductive castes and reproductive castes(division of labor, majority of individuals don't reproduce, maybe a queen, ex. wolves/ants)
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cooperative breeders
- species living in groups often cooperate in rearing offspring
- postpone reproduction
- what benefits do helpers gain?
- -inclusive fitness, improve survival and reproductive rates of family members
- -inherited territory, may increase helper's probability of future reproduction and recruiting helpers
- -kin selection, not the fitness at the level of the individual but at the level of the family instead, can occur at the level of the gene
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Naked mole rats&leaf cutter ants
has different duties in community but only the queen reproduces
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Natural selection
- some individuals in a population because of their phenotypic characteristics produce more offspring than themselves live to reproduce
- can favor, disfavor, or conserve the genetic makeup of a population
- proportion of favorable traits tend to increase
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Darwin's observations
- reproductive output is excessive
- most populations are stable
- resources are limited
- no two individuals are alike
- much of this variation in individuals is heritable
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Darwin's inferences
- Production of more individuals than the environment can support leads to a struggle for existence and only a fraction of offspring surviving to next generation
- Survival for existence is not random but is hereditary
- Those individuals with traits that best fit the environment will leave more offspring than less fit individuals.
- Favorable traits accumulate
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Gregor mendel
- Augustinian monk
- Studied garden peas
- Discovered characteristics pass from parent to offspring in the form of discrete packets called genes
- Genes exist in alternate forms and some prevent the expression of others
- Genes control heretibility/variability
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Evolution
- Change in gene frequency from one generation to the next
- Mutation creates new genes
- Evolution depends on death
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Conditions necessary for Hardy Weinberg
- Random mating
- No mutations
- Large population size
- No immigration
- Equitable fitness between all genotypes
- Likely, at least one of these will not be met and allele frequencies will change
- Potential for evolutionary change in natural populations is very great
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Change due to chance
- Random processes such as genetic drift can change gene frequencies in populations, especially small populations
- Habitat fragmentation is reducing habitat availability to the point where genetic drift will reduce genetic diversity within natural populations
- Genetic drift is not natural selection
- Genetic drift is important to conservation biology
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Genotype
Genetic makeup, affects phenotype
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Ecotypes
Different populations but different enough to distinguish
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Species
Capable of reproducing
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Variation within plants
- Evidence of adaption by ecotypes to local environmental conditions in potentilla glandulosa
- Individuals were transported from place to place, expected all plants to grow the same but results were different(nature vs. nurture)
- Common garden experiment with morphology
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Variation in animal populations
- Chuckwalla(herbivorous lizard in SW desert)
- Variation in rainfall translates into variation in food availability
- Rainfall and body length are directly proportional
- Plants still had difference in size when plants were moved
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Natural selection
- Changes genotypic and phenotypic frequencies in populations
- Some individuals in a population because of their phenotypic characteristics produce more offspring that themselves live to produce
- Natural selection can favor, disfavor, or conserve the genetic makeup of a population
- Proportion of favorable traits tend to increase
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Evolution by natural selection
- natural selection can result in adaption to the environment, depends on heritability of trait
- h2= VG/VP
- VP=VG+VE
- V
G=Genetic variance- V
P=Phenotypic variance- V
E=Variance due to environment
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Morphological difference
- Morphological difference is greatest with the greatest difference of vegetation
- Lizards introduced to islands with vegetation of greater difference in height compared to Staniel Cay display more morphological difference
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Rapid adaption by soapberry bugs
- Soapberry bug feeds on seeds from host plant
- Close relationship between fruit radius and beak length
- Can lead to speciation/production of new species
- Soapberry bugs living on host plant species with larger diameter fruits have longer beaks
- Directional selection
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Stabilizing selection
- Acts to impede changes in a population by acting against extreme phenotypes and favoring average phenotypes
- Tends to keep phenotype of population where it is today
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Directional selection
- Leads to changes in phenotypes by favoring extreme phenotypes
- Will eventually be stabilizing
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Disruptive selection
Creates bimodal distributions by favoring two or more extreme phenotypes over the average phenotype
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Tiger beetle of cold climates
- Tiger beetles live at higher latitudes and elevations than most other species in north america
- Found that metabolic rates are higher and preferred temperatures are lower than most other species
- Physical environment limits species distributions
- Poikilotherm/ectotherm
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Distributions of plants along a moisture-temperature gradient
- Encelia species distributions correspond to variations in temperature and precipitation
- More abundant in dry, hot areas but the species adapt and tolerate these conditions
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Distributions of barnacles along an intertidal gradient
- Depends of biotic conditions, competition, and credation
- Balonus settle throughout intertidal zone but survive to adults in the middle to lower intertidal zones
- Chthalamus settle in middle to upper but survive to adults in the upper
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Distributions of individuals on small scales
- Random-scattered
- Regular-uniform, antagonism
- Clumped- Attraction of individuals to a common resource. Barnacles(immobile as adults)
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Distribution of tropical bee colonies
- Hubbell and Johnson predicted aggressive non-colonial bee colonies would show regular distributions while non-aggressive species would show random of clumped distributions
- Species with regular distributions were highly aggressive
- Aggressive=regular
- Nonaggressive=random
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Distributions of desert shrubs
- Phillips and McMahon proposed as plants grow, some individuals in clumps die, reducing clumping
- Competition among remaining plants produces higher mortality, eventually creates regular disttributions
- Found competitive interactions with neighboring shrubs appear to influence distribution of creosote roots
- They release compounds into soil that inhibits other plants
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Distributions of individuals on large scales
Birds have random and clumped distributions
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density vs. body size
- small herbivores=high densities
- large herbivores=low densities
- same with organisms
- these are negative relationships, excludes humans
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Commonness and rarity
- 3 factors=geographic range of species, habitat tolerance, and local population size
- Populations that are least threatened by extinction have extensive geographic ranges, broad habitat tolerances, and large local populations
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Rarity 1
- Extensive range, broad habitat, and small local populations
- Peregrine Falcon
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Rarity 2
- Extensive range, large populations, narrow habitat tolerance
- Passenger pigeon
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Passenger pigeons
- Once abundant
- Flocks with 300 million birds per hour
- May have been most abundant ever existed
- Nested in long narrow colonies
- They were dispersers
- Only laid one egg at a time
- Needed big flocks for mating behavior
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Passenger pigeons and humans
- In 1878 a market hunter shipped 3 million birds where their last stronghold was held
- Last bird seen in 1900
- Martha died in 1914 in cincinnati zoo
- First time we knew the exact moment of a species extinction
- Sparked concern about conservation
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Rarity 3
- Restricted range, narrow habitat tolerance, small populations
- California condor, mountain gorilla
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How do plants disperse?
- Long distances through the wind
- With seeds
- Other plants can use fruits and animals
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How do barnacles disperse?
Barnacles disperse by larva, when competent, makes decision of places to settle and turns into non-mobile adults
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How do spiders disperse?
- Juvenile spiders transport by a string through the wind
- Very good at dispersing
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Africanized honeybees
- Exotic
- Most rapid dispersers
- Very good at migration, went from south america to north america
- Traveled across America 10 times faster than any other animal
- Didn't more further up north because it was too cold
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Collared doves
- Native species that decided to expand, moved quickly
- Majority didn't travel far
- Only few went far, increases variation
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Rapid changes in response to climate change
- Maple trees began to move north as climate warmed
- Didn't move individually
- Used to predict future responses due to anthropogenic effects
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Owls and kestrels
- Individual owls go where prey are
- Short time change responses
- Predators migrate because of prey
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Dispersal in rivers and streams
- stream dwellers have mechanisms to allow them to maintain their stream position
- Streamlined bodies-fish move upstream w/ little energy(angling body and using sideways currents)
- Bottom dwelling
- Adhesion to surfaces
- Tend to get washed downstream in spates(short term flood)
- Muller hypothesized populations maintained dynamic interplay between downstream and upstream
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Drift
going up to the water column and drift. Insects and fish do this to find more food, less predators. Insects do this at night
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Colonization cycle
- upstream and downstream dispersal and reproduction have major influences on stream populations
- dams have interfered with fish feeding and breeding grounds
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Udeodenum damns
- Gets eaten and hitchhikes to maintain position.
- Lays larvae inside of fish gills.
- Disperses fish
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Estimating patterns of survival=structure=age
- Cohort life table
- Static life table
- Age distribution
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Cohort life table
- Identify individuals born at the same time and keeps records from birth
- Follows one age group til last one dies
- Not oak trees
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Static life table
- Record age at death of individuals
- Estimate of age pattern of entire population
- Snapshot
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Age distribution
- calculate difference in proportion of individuals in each age class
- assumes differences from mortality
- today's population
- gets estimate about population growth/shrinking
- triangle=rapid, rectangle=steady
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Survivorship curves
- Generalized-some species have a mix
- Type 1=lots of old dying
- Type 2=consistent, same probability of dying
- Type 3=lots of young dying
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High survival among young
- Dall sheep
- Assumption: proportion of skulls in each age class represented typical proportion of individuals dying at that age
- Bi-modal mortality, <1 yr and 9-13 yrs
- Static life table, Type 1 curve
- Young skulls harder to find than old
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Type 2 survivorship curve
- Mud turtle
- Equal death rate at every age
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Type 3 survivorship curve
- Cleome
- lots of seeds with high death rates with young
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Rio grande cottonwood populations
- Old trees not being replaced
- Reproduction depends on seasonal floods(prepares seed bed&keeps nursery areas moist)
- Floods are absent because of dams, fewer germination areas
- Lots of 40&50 y/o trees, few really old trees.
- Huge decline in young because of no reproduction
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Grant's study
Age structure changed rapidly because dynamic age difference due to reproductive success and reproductive failure
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Why do population sizes change?
- Increases because of births and immigration
- Decreases because of deaths and emmigration
- Nt=No+B-D+I-E
- No=initial population
- Immigration and emigration are often ignored when considering world populations. Consider if in a cluster
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Exponential growth
- Continuous population growth in an unlimited environment can be modeled exponentially
- Appropriate for populations with overlapping generations
- As population size increases dN/dt gets larger
- dN/dt=rmaxN
- dN/dt= change in population size per unit time(slope)
- r=max per capita growth rate of a population(max intrinsic growth rate for animals producing millions of eggs)
- J shaped growth curve
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Exponential model
- growth by constant rate(2,4,8,16)
- Nt=No*ert
- er=#female offspring per individual
- t=time, expressed as number of generations
- dN/dt=rN
- Assumptions of exponential model=continuous reproduction, all organisms are identical, environment is constant in space and time
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Biotic potential
- All species have ability to reach infinite numbers in a short amount of time
- Decomposers can eat the corpses
- Fruit flys
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Exponential and Logistic models
- As N approaches 0, N/k is small or 0.
- When N is small, turns into exponential model
- When N approach K, turns less into logistic
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Logistic model
- dN/dt=rN(1-N/k)
- dN1/dt=rN1(1-N1/k1-p12n2/k1)
- density dependent vs density independent factors
- S-shaped
- competition is intraspecific in logistic
- N2=competitor sharing same resources
- k=carrying capacity
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Logistic population growth
- dN/dt=rN(1-N/k)
- as resources are depleted, population growth rate slows and eventually stops and stabilizes
- Sigmoid(s-shaped) population growth curve
- carrying capacity is the number of individuals of a population the environment can support
- As population size increases, logistic growth rate becomes a small fraction of growth rate
- Highest when N=k/2
- N/k=environmental resistance(intraspecific competition)
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limits to population growth
- environment limits population growth by altering birth and death rates
- Density dependent=disease, resource competition
- Density independent=natural disasters
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Easter island
- 400 AD colonized by polynesian
- Exponential growth
- Forest resources declined
- Exceeded k and the resources depleted
- Slavery and cannibalism also started happening
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Human population through time
- Rapidly increased from less than a billion to 7 billion
- Due to increase in death rates
- Industrial revolution
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Exercise in logic
- sustained positive exponential growth eventually leads to an infinite number of individuals
- Infinite numbers require infinite resources
- Earth is finite
- Therefore Earth cannot support sustained positive exponential growth
- There are two ways to reduce global population growth, decrease birth rates and increase death rates
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Earth's human carrying capacity
- Depends on lifestyle
- Antoni van Leeuwenhoek made first estimate
- Difficult to predict bc it depends on multiple moving factors
- Divide total amount of most limiting resource(law of the minimum) by the individual requirement for that resource
- Carrying capacity can change as populations change
- Most scientists say 10±3
- How much of earth's surface should be allocated to non-human species?
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Are we living sustainably?
- once growth surpasses sustainable yield interest, the resource based principle begins to dwindle
- mankind behaves towards environment the same way young people behave towards their finances(expect salary to raise) not how retired people behave(fixed income)
- exceeded sustainable yield of freshwater
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