Biology (cont.
)
Behavior ecology
• Behavior is an action carried out by muscles under control of the nervous
system
Animal physiology contributes to behavior and behavior influence
physiology
• Some behaviors rely on specialized body structures
Process of natural selection that shapes behavior also influences the
evolution of animal anatomy.
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Behavior answers the four questions
1. What stimulus triggers the behavior and how do the various body systems
bring it about?
2. How does the animal’s experience during growth and development
influence the response to the stimulus?
Proximate questions: how behavior occurs
3. How does behavior aid survival and reproduction?
4. What is the behavior’s evolutionary history?
Ultimate questions: why behavior arises
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Population
• Population: group of interbreeding
organisms of the same species
occupying the same area at the
same time
• Population is dynamic
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Population density
• Population density: the number of individuals of a given species in a unit of
area or volume
Quantifying population size and density
• Large organisms: visual counting or
photographing using unmanned aircraft
systems
• Sessile organisms (plants, algae, intertidal
animals):
• Quadrat
• Line transect
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Quantifying population size and density
• Mobile organisms:
• Pitfall trap: set up on the ground to
catch ants, lizards, snakes, spiders
• Mist net: hang between trees to catch
flying species such as flying birds and
bats
• Live trap (with baits) to catch small
animals such as rodents
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Quantifying population size and density
• Mark-recapture technique: the
caught individuals after being
released freely and randomly mixed
into the population
• Number of individual marked in first
catch/total population = number of
marked recaptures in second
catch/total number of second batch
• Assumption: no birth, no death, no
immigration or emigration
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Quantifying population size and density
• Other methods:
• For organisms which live in large herds: estimate population density based on number
of catch in a unit catch effort.
• For vocal organisms: identify and count chorusing or singing
• DNA-based technique (DNA fingerprinting technique)
Population dispersion
• Clumped: individuals are
aggregated in patches where
conditions are favorable to growth of
a species
• Clumping is also associated with
mating behavior
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Population dispersion
• Uniform: evenly spaced, associated
with direct competition between
individuals
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Population dispersion
• Random: the position of each
individuals in a population is
independent of each other
• Caused by:
• Randomly distributed resources
• Windblown seeds are randomly
distributed
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Reproduction strategies
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Survivorship curve reveal different patterns of survival
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How populations grow
• Exponential growth occurs when
resources are not limiting
• Logistic growth occurs when
resources are limited
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Hardy-Weinberg equation
• Hardy-Weinberg equilibrium: in a
population that is not evolving, allele
and genotype frequencies remain
constant from generation to
generation
• By random mating, genotype of
offspring can be determined
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Conditions for Hardy-Weinberg equilibrium
Condition Consequence if condition does not hold
No mutation The gene pool is modified if mutation occur or if
entire genes are deleted or duplicated
Random mating Random mixing of gametes does not occur and
genotype frequencies change
No natural selection Allele frequency change when individuals with
different genotypes show consistent differences in
their survival or reproductive success
Extremely large population size In small population, allele frequencies fluctuate by
chance over time (genetic drift)
No gene flow By moving alleles into or out of populations, gene
flow can alter allele frequencies
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Genetic variation makes evolution possible
• Phenotypic variation often reflect genetic variation: differences among
individuals in the composition of their genes
• For example, flower color, height, seed shape, seed color of pea plants
A determines round seeds; a determines wrinkled seeds
B determines tall plants; b determines dwarf plants
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Genetic variation at the molecular level
• Genetic variation can be measured at the molecular level of DNA
• Not all nucleotide variation results in phenotypic variations,
E.g., only one substitution in the alcohol dehydrogenase (adh) gene at
position 1490 results in a change in the amino acid sequence of the
protein and make a non-functional form of adh gene
• Genetic variation provide materials for evolutionary changes.
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Molecular processes that underline
evolution
• Formation of orthologs and paralogs,
horizonal gene transfer, changes in
chromosome structure and number
• Homologous genes derive from the same
ancestral gene.
• Homologous genes are found in different
species are orthologs, and are found within
an individual’s genome are called paralogs,
often resulted from gene duplication
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Microevolution occurs due to:
• Genetic variation (introduction of new allele into the gene pool of the
population) by mutation, change in chromosome structure and number,
horizontal gene transfer
• Events that lead to the change in allele frequency:
• Natural selection
• Genetic drift
• Sexual selection
• Migration
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Natural selection favors individuals with greater reproductive success
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Natural selection favors individuals with greater reproductive success
• Directional selection occur when a population’s
environment changes or when members of a
population migrate to a new and different
habitat.
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Natural selection favors individuals with greater reproductive success
• Disruptive selection occurs
when conditions favor
individuals at both
extremes of a phenotypic
range
• E.g., seed eating birds
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Natural selection favors individuals with greater reproductive success
• Stabilizing selection: acts against both extreme
phenotypes and favors intermediate variants
which reduces variation.
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Natural selection alters populations over time
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Genetic drift is the change in allele frequency due to random chance
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The founder’s effect
• When a few individuals become isolated from a larger population, this small
group may establish a new population whose gene pool differs from the
source population → the founder’s effect
• E.g., in 1814, British colonists who settled on Tristan da Cunha carried a
recessive allele for retinitis pigmentosa. The frequency of the allele that
cause the disease is ten times higher than in the original population
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The bottleneck effect
• A sudden change in the environment may drastically reduce the size of a
population. A severe drop in population size can cause bottleneck effect
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Effects of genetic drift
• Significant in small populations
• Can cause allele frequencies to change at random
• Can lead to a loss of genetic variation within populations
• Can cause harmful alleles to become fixed (frequency = 100%)
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Sexual selection
• Sexual selection: individuals with certain inherited characteristics are more
likely than other individuals of the same sex to obtain mates.
• Intrasexual selection: selection within the same sex, individuals of one sex
compete directly for mates of the opposite sex
• Intersexual selection (mate choice): individual of one sex are choosy in
selecting their mates from the other sex. Females prefer male traits that are
correlated with “good genes”
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Migration between two populations tends to increase genetic variation
• Migration alter allele frequencies in
certain alleles in the population.
• The transfer of alleles into or out of
the population is “gene flow”
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Natural selection alters populations over time
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The basis of identifying a species: Reproductive isolation
• Reproductive isolation: Individuals belonging to different species cannot
interbreed with each other (sexually reproducing organisms) → reproduction
isolation is used to identify 2 populations as 2 distinct species
• Biological species concept: group of individuals with a potential to interbreed
to produce viable and fertile offspring.
• Biological species concept focuses on reproductive isolation – a barrier
to prevent individuals of two species interbreed
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Reproductive isolation: Habitat isolation
Apple maggot fly (Rhagoletis pomonella) Blueberry maggot fly (R. mendax)
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Reproductive isolation: Temporal isolation
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Reproductive isolation: Behavioral isolation
• Mating behavior and anatomy of
the male animal attract the female
of the same species, not the other
species
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Reproductive isolation: Behavioral isolation
• Environmental condition may contribute to reproductive isolation
→ By-product of adaptation for feeding is reproductive isolation
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Reproductive isolation: Mechanical isolation
• Incompatible morphological features
prevents individuals of two species to
mate with each other.
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Reproductive isolation: Hybrid invisibility
• Fertilized eggs resulting from interspecies mating stop developing
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Reproductive isolation: Hybrid sterility
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Reproductive isolation: hybrid breakdown
• Hybrids may viable and fertile, but they are unable to produce viable offspring
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Mechanisms of speciation
• Accumulation of sufficient genetic changes resulting in sufficient
morphological differences for a population to be identified as a novel species.
• Due to:
• Abrupt events
• Adaptation to new environment (leads to reproductive isolation in sexually reproducing
organisms)
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Adaptive radiation results in multiple novel species from a single one
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Adaptation to environmental condition leads to reproductive isolation
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Speciation takes place at the same location: sympatric speciation
• Sympatric speciation occurs in three possible ways:
• Polyploidy
• Adaptation to local environments
• Sexual selection
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Species interactions
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Competition
• Competition: -/-
• Competitive species use the same
resource that limits the survival and
reproduction of both species.
• Interference competition: direct
interaction by physical force or
intimidation
• Exploitation competition: indirect
interaction by consumption of limited
resource
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Strategy for different species to share the same habitat
• Resource partitioning: • Character displacement: the ability
differentiation of niches, both in of species to change their
space and time, enable similar morphological properties that
species to coexist affect their ability to use resources
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Predation, Herbivory, and Parasitism
• Species interaction: +/-
• Predation results in the death of a prey
• Herbivory involves nonlethal predation
on plants
• Parasitism involves in nonlethal and
longterm predation on a host
• Parasitoid involves in longterm
predation on a host and ends up in the
death of the host.
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Predation affect prey densities
• 72% of the nearly 1500 predator-
prey studies showed a large
depression of prey density by
predators
• Feeding adaptations of predators:
• Acute senses that enable them find and
identify preys
• Claws, fangs, poisons that subdue
preys quickly and efficiently
• Fast and agile or lie in ambush
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Strategies to avoid predation
• Chemical defense: some animals can
synthesize toxins to avoid being eaten by
predators
• Aposematic coloration: warning color
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Strategies to avoid predation
• Camouflage: blending of an • Display of intimidation: to
organism with the background of its discourage predators
habitat
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Strategies to avoid predation
• Muellerian Mimicry • Batesian mimicry
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Strategies to avoid predation
• Mechanical defense:
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Herbivores have dramatic effects on plant populations
• Insect herbivore (cactus moth: Cactoblastis cactorum) helps control the
population density of prickly pear cactus
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Parasitism is a common way of life
• A parasite may have complicated life cycles and
involves in multiple hosts.
• High host density might help increase parasite’s
population density
• Holoparasites: flowering plants live on other plants
and lack chlorophyll
• Hemiparasites: can carry out photosynthesis but
depend on others for minerals
• Monophagous/polyphagous: one or more than one
hosts
• Ecto/endoparasites: live on or inside a host
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Positive interactions: mutualism (+/+)
• Resource-based mutualism: Leaf-cutter
ant (Atta cephalotes) and fungi
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Positive interactions: mutualism (+/+)
• Defensive mutualism: Acadia tree and stinging ant (Pseudomyrmex)
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Positive interactions: mutualism (+/+)
• Defensive mutualism: Red carpenter ant (Camponotus ferrugineus) and
aphids
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Positive interactions: mutualism (+/+)
• Dispersive mutualism: plant-animal interaction which involves in pollination
and seed dispersal, can be obligatory or facultative
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Positive interaction: commensalism (+/0)
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Significance of species interaction
• Bottom up control: • Top down control:
Food limitation natural enermies
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Significance of species interaction
• Mark Hebblewhite study in Banff National Park
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