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Ecology
Week 1 - Introduction to Ecology
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Ecology (from the Greek oikos, house) is the scientific study of the abundance and distribution
of organisms in relation to other organisms and environmental conditions
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Acquire nutrients and energy and produces
waste
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Density - no
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Community - populations living together
Ecosystems - one or more communities of living organism interacting
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A
dynamic steady state occurs when gains and losses are in balance
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Evolutionary patterns - prokaryotes and archea were first organisms
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Species categorized based on energy - producer/ consumers ect
or types of species interactions - predation/competition ect
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Studying ecology - scientific method, natural/ manipulative experiment
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Life history: the schedule of an organism’s growth, development, reproduction, and survival;
represents an allocation of limited time and resources to achieve maximum reproductive
success
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Parity: the number of reproductive episodes an organism experiences
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Longevity (life expectancy): the life span of an organism
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Principle of allocation: the observation that when resources are devoted to one body
structure, physiological function, or behavior, they cannot be allotted to another
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There is a tradeoff between offspring number and offspring survival
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G
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parental survival, growth rate vs
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Organisms differ in the number of times they reproduce before senescence
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Iteroparity: when organisms reproduce multiple times during their life; common among birds,
reptiles, mammals, and amphibians
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Perennial: an organism that has a life span of more than one year
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Environmental conditions - stimuli for change, e
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Resource availability
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Week 2 - Populations
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The distribution of populations is limited to ecologically
suitable habitats:
Spatial structure: the pattern of density and spacing of individuals in a population
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g
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Competitors, predators, and pathogens may prevent a
population from persisting in an area
Realized niche: the range of abiotic and biotic conditions under which a species can persist
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Ecological niche modeling: the process of determining the suitable habitat conditions for a
species
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Ecological envelope: the range of ecological conditions that are predicted to be suitable for a
species (differs from the realized niche, which describes conditions in which a species currently
exists)
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Population characteristics:
Endemic: species that live in a single, often isolated, location
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Abundance: the total number of individuals in a population that exist within a defined area
(e
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, total number of lizards on a mountain)
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Density: in a population, the number of individuals per unit area or volume; calculated by
dividing abundance by area
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Dispersion: the spacing of individuals with respect to one another within the geographic range
of a population
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Dispersal: the movement of individuals from one area to another
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It
is the mechanism by which individuals can move between suitable habitats
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Dispersal can be a way to avoid
areas of high competition or high predation risk
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These can be Area or volumes based
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Mark-recapture survey: a method of population
estimation in which researchers capture and mark a subset of a population from an area,
return it to the area, and capture a second sample of the population after time has passed
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Lifetime dispersal distance: the average distance an individual moves from where it was born
to where it reproduces
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This pattern has been
observed for many organisms (e
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, birds)
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The large amount of
variation in the abundance-range size regression may be caused by fluctuations within a
geographic range
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g
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From this relationship, we expect a given plot of habitat to support fewer large individuals
than it does small individuals
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Barriers often include large expanses of inhospitable habitat
that an organism cannot cross (e
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, oceans, deserts)
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g
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Habitat corridor: a strip of favorable habitat located between two large patches of habitat that
facilitates dispersal (e
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, a narrow band of trees that connects forests)
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Distribution:
When possible, individuals choose habitats that provide the most energy
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Per capita benefit
can fall so low that an individual would benefit by moving to the low-quality habitat
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Individuals in nature rarely meet the expectations required by the ideal free
distribution
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Fitness is not solely
determined by maximizing resources; other factors may influence distribution such as the
presence of predators or territory owners
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When individuals frequently disperse among
subpopulations, the whole population functions as a single structure; all subpopulations
increase and decrease in abundance synchronously
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Basic metapopulation model: a model that describes a scenario in which there are patches of
suitable habitat embedded within a matrix of unsuitable habitat; all suitable patches are
assumed to be of equal quality
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Source subpopulation: in high-quality habitats, subpopulations that serve as a source of
dispersers within a metapopulation
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Landscape metapopulation model: a population model that considers both differences in the
quality of the suitable patches and the quality of the surrounding matrix (e
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, habitat
corridors)
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Week 3 - Population Ecology
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Population demography - he study of populations
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Intrinsic growth rate (r): the highest possible per capita growth rate for a population
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e
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Exponential growth model: a model of population growth in which the population increases
continuously at an exponential rate; can be described by the equation:

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Nt = future population size; N0 = current population size, r = intrinsic growth rate; t = time over
which a population grows, e = approx
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71828
The rate of a population’s growth at any point in time is the derivative of this equation:

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Geometric growth model - a model of population growth that compares population sizes at
regular time intervals
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When λ > 1, population size has decreased;
λ cannot be negative
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When a population is constant, λ = 1 and r =
0
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See above for graphs
Doubling time: the time required for a population to double in size; can be estimated by
rearranging the exponential growth model:

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Density independent: factors that limit population size regardless of the population’s density
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g
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Density dependent: factors that affect population size in relation to the population’s density
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Self-thinning curve: a graphical relationship that shows how decreases in population density
over time lead to increases in the size of each individual in the population; often has a slope of
-3/2
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The most common factors that cause negative density dependence are
limiting resources (e
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, food, nesting sites, physical space)
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Crowded populations can also generate stress, transmit disease, and attract predators
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Typically occurs when population densities are low, which may make it hard

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to find mates, particularly when sex ratios are uneven
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Populations are often regulated by both positive and negative density dependence
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Above some density, resources become limiting and negative density dependence begins to
play a role
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Rate of per capita increase can be
modeled as:

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Survivorship curve - A type I survivorship curve depicts a population that experiences low
mortality early in life and high mortality later in life (e
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bears, humans, elephants, whales)
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g
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A type III curve depicts a population with high mortality early in life
and high survival later in life (e
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, weeds)
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x = age class,
nx = the number of individuals in each age class immediately after the population has
produced offspring, sx = the survival rate from one age class to the next age class, bx = the
fecundity of each age class
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Number of new
offspring produced = (nx) x (sx) x (bx)
Stable age distribution: when the age structure of a population does not change over time;
occurs when survival and fecundity of each age class stays constant over time
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Population fluctuations - All populations experience fluctuations due to factors such as
availability of resources, predation, competition, disease, parasites, and climate
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Some populations tend to remain relatively
stable over long periods
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Small organisms (e
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, algae) tend to reproduce much faster than larger organisms (e
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, red
deer), so their populations often respond faster to favorable and unfavorable conditions
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Populations in nature rarely follow a smooth approach to their carrying capacity:
Overshoot: when a population grows beyond its carrying capacity; often occurs when the
carrying capacity of a habitat decreases from one year to next (e
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, because less resources are
produced)
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Die-offs often occur when a population overshoots its carrying capacity
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Population cycles: regular oscillation of a population over a longer period of time
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Cyclic populations can occur among
related species and across large geographic areas
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Overshoots can
occur when there is a delay between the initiation of breeding and the time that offspring are
added to the population
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As the time delay increases, density dependence is delayed and the population is more prone
to both overshooting and undershooting K
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When 0
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57, the population exhibits damped oscillations
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When rτ > 1
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Stable limit cycle: a pattern of population growth in which the population continues to exhibit
large oscillations over time
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Delayed density dependence can occur when there is a time delay in development
from one life stage to another
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Stochastic model: a model that incorporates random variation in population growth rate;
assumes that variation in birth and death rates is due to random chance
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Environmental stochasticity: variation in birth rates and death rates due to random changes in
the environmental conditions (e
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, changes in the weather)
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Often occurs as a result of human activities (e
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, clearing forests, road construction,
draining wetlands)
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Sources are high-quality patches that produce a large number of individuals that disperse to
other patches
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If subpopulations rarely exchange individuals, fluctuations in abundance will be independent
among subpopulations
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Unoccupied patches that are close to occupied patches are more likely to be colonized
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Less isolated patches are more likely to be rescued and are also more likely
to be colonized
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e
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Week 4 - Herbivores and predation
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Predators - Natural enemies are critical in communities as they lower the population size of
their victims
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Natural enemies - predators, pathogen, parasites, parasitoids, herbivores
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Coexistence of predators and prey determined by
immigration
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Effects of predators - Introduced, exotic, or non-native species are introduced to a region of
the world where they have not historically existed
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Parasitoids - unique type of predator that limit abundance of prey, e
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Parasitoids wasp -lays
eggs inside hose and eats the organism from the inside
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Top predators - consume both herbivores and predators - wolves, sharks ect
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This has had dramatic effects on
mesopredator prey populations
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The effects of
herbivores may be seen by fencing areas or removing herbivores to prevent grazing
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stable predator-prey population cycles can be achieved when the environment is complex so
that predators cannot easily find prey
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Growth of prey populations depends on the growth rate of a prey population (rN) and
the rate of individuals killed by predators (cNP):

Similarly, growth of predator populations depends on growth rate of predator populations
(acNP) minus the rate of predator death (mP):

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Prey population is stable when its rate of change is zero:

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Hence, a prey population is stable when the addition of prey is balanced by the consumption
of prey
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As the number of predators or prey changes and
moves away from the equilibrium isoclines, populations will increase or decrease
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Whenever prey density increases and a predator can consume a
higher proportion of those prey, the predator can regulate the growth of the prey population
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As prey density increases, predators consume a constant
proportion of prey until satiation
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Any increase in prey density is associated with a slowing
rate of prey consumption
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Low
consumption at low prey densities may occur for three
reasons: Prey can easily find refuges to hide, Predators
may have less practice at locating and catching prey but
develop a search image at higher prey densities - Search
image: a learned mental image that helps a predator locate and capture food
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Numerical response: a change in the number of predators through population growth or
population movement due to immigration or emigration
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Herbivore population dynamics - 2 types: interactive herbivore system - herbivores affect plant
population traits, non-interactive - no relationship between herbivore densities and plant
population
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Some prey reduce activity to
avoid being detected by a predator
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g
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Structural defenses reduce a predator’s ability to
capture, attack, or handle prey
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Warning coloration
(aposematism): a strategy where distastefulness evolves in association with very conspicuous
colors and patterns
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Batesian mimicry: when palatable
species evolve warning coloration that resembles unpalatable species
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Behavioral defenses are often costly because they result in reduced feeding activity or
crowding in locations away from predators
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Defense costs can reduce growth, development, and reproduction
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Defenses against herbivores - Selective pressure from herbivores has caused the evolution of
plant defenses; some have phenotypically plastic defenses induced by attack, whereas others
have fixed defenses
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g
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Chemical defenses include sticky resins and latex
compounds that are hard to consume, and alkaloids (e
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, caffeine, nicotine, morphine) that
have a wide range of toxic effects
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Consumes host resources
Causes harm to host
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 Endoparasites - live on the outside of an organism
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Intercellular: live in spaces between cells of a host
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Prions - incorrect
protein fold causes it to be pathogenic
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Very difficult to
obtain information on levels of infection & mortality
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Often occurs
when a mutation allows a pathogen to jump to a new
host species
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Mainly
arthropods - mites, lice, fleas
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 Parasite and host dynamics - Populations of hosts and parasites fluctuate over time
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Factors that influence the probability of host
infection:
o Mechanism of transmission - Horizontal transmission: When a parasite moves between
individuals other than parents and offspring
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o Mode of entering the host - Piercing tissue, reliance on a vector
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They can be a continuous source of parasites as other hosts become rare
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g
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Form protective outer layer (e
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, schistosomes)

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Vector - an organism that dispersed a parasite between hosts
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 Population fluctuation - Density of hosts can affect how easily parasites are transmitted from
one host to another
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Infection resistance: ability of host to prevent infection from
occurring (e
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, through immune response or behavior)
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Vaccinations can control infection resistance
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S = Number of individuals susceptible to a
pathogen
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R = Number of individuals that
develop resistance
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g = rate of
recovery and development of immunity
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If R0 < 1, the infection fails to spread
 Parasites can evolve adaptations that increase the probability of transmission
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Immune system responses
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Mechanical/biochemical defenses
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Mutualism:
 A mutualism is a positive interaction between two species in which one species receives
benefits that only the other species can provide
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 Generalists: a species that interacts with many other species
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Obligate mutualists: two
species that provide fitness benefits to each other and require each other to persist
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 Many plants rely on mutualisms with fungi and bacteria to help them obtain nutrients
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Endomycorrhizal fungi: fungi characterized by hyphal threads that extend far out into the soil
and penetrate root cells between the cell wall and the cell membrane
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Fungal hyphae provide plants with soil minerals
(e
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, nitrogen) and water; plants provide the fungi with sugars from photosynthesis
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Arbuscules are
branching hyphal structures found within plant cells that help the fungus to provide nutrients
to the plant
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The mutualism between plants and mycorrhizal fungi goes back more than 450 mya to the
time when plants first evolved on land
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Mutualistic interactions between plants and bacteria convert unusable forms of minerals into
forms that plants can use
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Many plants have mutualisms that defend them from enemies
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Endophytic fungi produce chemicals that repel herbivores and provide drought
resistance by increasing the concentration of minerals in plant tissue
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g
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Pollination - Many plants rely on animals to carry pollen between flowers
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The plants ‘want’ to invest as little as possible in feeding bees
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The bees ‘want’ to invest as little as possible in foraging
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Bees can rapidly learn to associate flower characteristics with pollen rewards
Floral odour can be learned in one trial with a reliability of 93-100%
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Shapes and patterns hardest to learn - takes 10-30 trials
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Critical role in community structure
Economics - 30% of human food comes from bee pollinated plants
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California 2010 – 1
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Burkle et
al
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One of the most common benefits is food in the form of seeds
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Each individual participates in a mutualism to improve its own fitness, not that of its partner
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g
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Cheating occurs when one species receives a benefit but does not provide one in
return
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The disruption of a mutualism may cause a decline of the species involved and a reduction in
their distribution
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Loss of dispersers an result in a reduction
in plant abundance
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Competition - Occurs when individuals experience limited resources
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Negative density dependence is a common type of intraspecific competition, where an
increase in a population’s density causes a decline in the growth rate of the population
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Interspecific competition can cause the population of one species to decline and eventually die
out
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Ecological factors, e
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Temp, are not included,

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however for plants sunlight, water and soil, for animals includes food and space
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E
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Increased light and fertilizer causes plants to
grow much more than with neither
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law stating that a
population increases until the supply of the most limiting resource prevents it from increasing
further
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Competitive exclusion principle - two species cannot coexist indefinitely when they are both
limited by the same resource
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Darwin suggested that competition is most intense between related species because they
have similar traits and consume similar resources
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Competition can also be intesne
among distantly related species that consumer a common resource, e
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Space on rocks for
barnacles and mussels
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To include a second species add the number of individuals of the second species and how they
affect carrying capacity of first species
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To determine the conditions under which one species will have a population at equilibrium
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Zero population growth isocline - population sizes at which a population experiences zero
growth
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When the population of species 1 is to the left of
the isocline, it will experience population growth
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For species 2:

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Predicting outcome - When K1 and K2 are the most extreme points on the axes, there are two
possible equilibria:
1
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2
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When K1 and K2 are the innermost points on the axes, net movement is to a single equilibrium
point where the lines cross
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e
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Abiotic conditions - The ability to compete well may be overwhelmed by the ability to persist
in harsh abiotic conditions
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g
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Predation and herbivory - There are often trade-offs between competitive ability and
resistance to predators or herbivores; the most competitive organisms are often the most
susceptible to predation or herbivory
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Herbivores can alter competition as they can eat plants that shade other plant competitors
etc
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Exploitative
competition is considered indirect competition because it occurs through a shared resource
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Allelopathy - a type of interference competition
that occurs when organisms use chemicals to harm their competitors
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Apparent competition could be
generated if one species facilitates the enemy of another species
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Species composition changes across a landscape; with changes in environmental conditions,
some species are better able to survive
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Ecotone - a boundary created by sharp changes in environmental conditions over a relatively
short distance, accompanied by a major change in the composition of species
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Ecotones support a large number of species, including those from adjoining
habitats, and species specifically adapted to the ecotone
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Sharp changes in the distribution of species should
occur across the ecotone
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If species distributions are independent, they should depend only on individual habitat
requirements; there should be gradual changes in species along a line transect
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g
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If
species are interdependent, removing a species should cause other species to decline; if
species are independent, removing a species should cause neutral or positive changes in other
species’ fitness
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g
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Species richness - the number of species in a community
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Relative abundance - proportion of individuals in a community represented by each species
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To
plot a rank-abundance curve, rank each species in terms of its abundance; the most abundant
species receives a rank of 1, the next most abundant species receives a rank of 2, etc
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Correlation between richness and productivity has shown a wide range of patterns:

Across studies of vertebrates and invertebrates in aquatic and terrestrial systems, a humpshaped curve is the most commonly observed relationship between diversity and productivity
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Experiments have manipulated productivity by adding
nutrients (e
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, nitrogen) to an ecosystem
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g
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Effect of habitat diversity - Communities with a higher diversity of habitats should offer more
potential niches (e
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, places to feed and breed) and a higher diversity of species
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Ecosystem engineers affect communities by influencing the structure
of a habitat, e
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Beavers building dams
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When disturbances are rare,
populations grow until resources are scarce, and competitively superior species become
dominant
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When disturbances occur at an intermediate
frequency, both types of species can persist
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Food web - complex and realistic representation of how species feed on each other in a
community, arrows indicate consumption and movement of energy and nutrients
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Producers are the
autotrophs that convert light energy and CO2 into carbohydrates through photosynthesis
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Primary consumer: a species that eats producers
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Tertiary consumer: a species that eats secondary consumers
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Guild: within a given trophic level, a group of species that feeds on similar items (e
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, guilds of
leaf eaters); members of the group are not necessarily related
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The
direct effect of one species often sets off a chain of events that affect other species in the
community
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Exploitative competition is an indirect effect; two competitors are interacting by feeding on a
third species, which is a common resource
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Trophic cascade: indirect effects in a community that are initiated by a predator
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Trait-mediated indirect effect: an indirect effect caused by changes in the traits of an
intermediate species
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Bottom-up control - When the abundances of trophic groups are determined by the amount of
energy available from producers
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Community stability - Ability to maintain a particular structure
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Community resilience - the time it takes after a disturbance for a community to return to its
original state
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Alternative stable state: when a community is disturbed so much that species composition and
relative abundance change, and the new community structure is resistant to further change
...
g
...


Week 7 - Community succession, landscape ecology
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Succession - the process by which the species composition of a community changes over time
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Pioneer species - the earliest species to arrive at a site; typically are able to disperse long
distances and arrive quickly at disturbed sites
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Observing succession - Direct observation of changes over time is the clearest way to record
succession in a community
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Chronosequence: a
sequence of communities that exist over time at a given location
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Flowering plants produce pollen grains with distinct sizes and shapes that travel
through the air and land on a lake surface
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Researchers can take a sample that penetrates
through many layers of mud on the lake bottom
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Primary succession - the development of communities in habitats that are initially devoid of
plants and organic soil, such as such dunes, lava flows, and bare rock
...
g
...
g
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Early colonizers produce organic matter that helps in the creation of
soil that generates more hospitable conditions for other species
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g
...
The use of chronosequences

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assumes that older and younger sites pass through similar seral stages
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Animal succession - changes in the plant community can change the habitats that are available
to animals which causes changes in the animal community
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Stream succession - Streams undergo rapid succession because organisms can move
downstream from sites that are less disturbed
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Lake succession - most models suggest slow transformation
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Changes in species diversity - After a disturbance that eliminates most or all species in a
community, species richness is at or near zero
...
This pattern is consistent across
most cases of succession
...

Mechanisms of succession Facilitation: a mechanism in which one species increases the probability that a second species
can become established
...
g
...
Early in succession,
inhibition can prevent movement toward a climax community
...

Priority effect: when the arrival of species at a site affects the colonization of other species;
often occurs through inhibition
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Changes in climax communities - As succession occurs, we typically observe changing
environmental conditions and a progression from small to large life forms
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When environmental
conditions are stable, the composition of plant species in a community also becomes stable
...

Transient climax communities - a climax community that is not persistent; occurs when a site is
frequently disturbed so a climax community cannot persist
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Fire-maintained climax community: a successional stage that persists as
the final seral stage due to periodic fires
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Grazers preferentially
consume the most palatable plants, leaving behind less palatable or better-defended species
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Current habitat heterogeneity is a reflection of recent and historical events
caused by natural and human forces
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Habitat heterogeneity - Natural forces (e
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, tornadoes, hurricanes, floods, mudslides, fires)
continue to cause habitat heterogeneity
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Humans act as ecosystem engineers by
constructing buildings, dams, irrigation channels, etc
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Species richness often increases from the local to landscape scale because habitat diversity
increases along this gradient
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e
...
Regional (i
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, gamma) diversity: the
number of species in all of the habitats that comprise a large geographic area
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Regional species pool:
the collection of species that occurs within a region; serves a source of species of all local sites
within a region
...

To make it easier to work with this equation in the form of a graph, we can take the logarithm
of both sides
...


Habitat fragmentation - human activities has causes widespread fragmentation of large
habitats throughout the world
...
g
...
Fragmentation decreases habitat area and
increases patch number, edge size, and isolation
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Fragmentation causes an increase in the amount of edge habitat
compared to the original unfragmented habitat
...
g
...
Species that prefer edge habitat increase in abundance when fragmentation occurs
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Corridors increase gene flow and genetic
diversity
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Habitat between fragments - The quality of habitat between fragments (i
...
, matrix habitat)
helps to determine whether organisms can move between fragments
...

Equilibrium theory of island biogeography: a theory stating that the number of species on an
island reflects a balance between the colonization of new species and the extinction of existing
species
...
g
...
Assuming the species pool of potential colonizers is a
fixed size, then the rate of new species colonizing the island declines as a function of how
many species have already colonized the island
...
g
...
Given that the island continues to experience colonization
and extinction of species, these opposing forces should result in an equilibrium point of
species richness on the island Ŝ
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At equilibrium, there is a continuous
turnover of species, resulting in a temporally variable species composition
...
Combining the effects of island area and isolation reveals predictions
regarding Ŝ
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Latitudinal trends in diversity are pervasive and
extend even to the oceans
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Mammal species richness also increases to the
west, likely due to the habitat heterogeneity of mountains
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The number of species found in a given location is positively correlated to the amount of solar
energy and precipitation
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PET often positively
correlates with species richness, but eventually plateaus as increasing temperature becomes a
stressor
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Higher energy inputs may
accelerate evolution and speciation rates
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Temperature latitudes experience
seasonal peaks in marine productivity due to seasonal mixing of water
...
A temperature-productivity relationship in marine environments provides further
evidence to support the energy-diversity hypothesis
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Pangaea: the single landmass that existed on Earth ~250 Mya and subsequently split into
Laurasia and Gondwana
...

Gondwana: the southern landmass that separated from Pangaea and split into South America,
Africa, Antarctica, and India
...
The separation and joining of continents established six distinct biogeographic
regions that contain unique groups of organisms
...
These changes have had profound effects on the
distributions of plants and animals
...
Alternating periods of cooling and warming
caused the advance and retreat of ice sheets over North America and cycles of cool, dry
climates and warm, wet climates in tropics
...
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Week 8 - Biomes and conservation
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Terrestrial biomes - Biomes: geographic regions that contain communities composed of
organisms with similar adaptations
...
Boundaries between biomes can be unclear
...
Biomes can be depicted inside a triangular area with corners representing warm
moist, warm dry, and cool dry climates
...
There are nine biomes within three temperature ranges: < 5°C, 5°C–20°C, and > 20°C
...
Growing season: months that are warm enough to allow plant
growth (i
...
, temperatures > 0°C; see shaded months in diagrams)
...

Tundras - The coldest biome, characterized by a treeless expanse above permanently frozen
soil (permafrost)
...

Precipitation is < 600 mm
...
Plants grow low to the ground to
gain protection under snow and ice
...
Temperatures are < 5°C (as low as –60°C) and rainfall is
50–1,000 mm
...
Soils are acidic and podsolized
...

Temperate rainforests - A biome known for mild temperatures and abundant precipitation,
and dominated by evergreen forests
...
In North America, these forests are dominated by coast redwood and Douglas fir that
can be 60–70 m tall
...

Temperate seasonal rainforests - A biome with moderate temperature and precipitation
conditions, dominated by deciduous trees (e
...
, maple, beech, and oak)
...
Precipitation exceeds transpiration
...

Warmer and drier parts of the biome are dominated by pines
...

(Also known Mediterranean climate, chaparral, matorral, fynbos, and maquis
...
Dominated by schlerophyllous vegetation, which has small and durable leaves
that resist dessication
...
) Tallgrass prairies occur when rainfall is high;
shortgrass praires occur in areas with less precipitation
...
Unproductive, cold deserts occur when precipitation <250
mm
...
There is a canopy of 30–40 m trees with an understory containing
smaller trees, shrubs, epiphytes, and vines
...
Organic matter decomposes quickly; vegetation rapidly takes up nutrients
...

Tropical seasonal forests / savannas - A biome with warm temperatures and pronounced wet
and dry seasons (due to movement of the intertropical convergence zone), dominated by
deciduous trees that shed leaves during the dry season
...
Fire and grazing maintain savannas
...

Subtropical deserts - biome characterized by hot temperatures, scarce rainfall, long growing
seasons, and sparse vegetation
...
Soils are
shallow and devoid of organic matter, and neutral in pH
...
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...

Streams and rivers - Lotic: characterized by flowing water
...
River: a wide channel of slow-flowing fresh water
...
Streams support
fewer species than other aquatic biomes
...
Riparian zone: terrestrial vegetation alongside rivers and
streams that is influenced by seasonal flooding and elevated water tables
...
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...
Autochthonous: Inputs of organic matter that are produced by algae and
aquatic plants inside an ecosystem
...

Rivers typically accumulate sediments from land, and high turbidity can block light and reduce
primary production
...
Lake: An aquatic biome that is larger than a pond and is characterized by nonflowing fresh water with some area of water that is too deep for plants to rise above the
water’s surface
...
Oxbow lakes are broad bends of what was once the
river, cut off by shifts in the main channel
...
Limnetic (pelagic) zone: the open water beyond the littoral zone, where the
dominant photosynthetic organisms are floating algae (i
...
, phytoplankton)
...
Benthic zone: the area with sediments at the bottom of lakes, ponds, and oceans; is
habitat for burrowing organisms
...
Hypolimnion: the deeper layer of water in a
lake or pond; can include the lower limnetic profundal zone
...

Most production occurs in the epilimnion, which is well-aerated
...

Circulation - Seasonal temperatures alter water density; water becomes more dense as it cools
to 4°C and less dense as it cools below 4°C
...
Spring overturn: the vertical mixing of lake water that occurs in early
spring, assisted by winds that drive the surface currents
...

Fall overturn: the vertical mixing that occurs in fall, assisted by winds that drive the surface
currents
...
Fall bloom: a rapid increase in the population of
phytoplankton in fall that occurs with the infusion of nutrients from fall overturn
...
Wetlands provide animal habitat, and are important natural
purification systems
Salt marshes/ estuaries - Salt marshes: a saltwater biome that contains non-woody emergent
vegetation
...
Estuaries contain abundant nutrients and
sediments carried downstream by rivers
...

Estuaries are often surrounded by tidal marshes, which are some of the most productive
habitats on Earth
...
- Mangrove swamps: a biome that occurs along tropical and subtropical
coasts, and contains salt-tolerant trees with roots submerged in water
...
Mangrove trees prevent the
erosion of shorelines from incoming waves
...

Intertidal zones - Intertidal zones: a biome consisting of the narrow band of coastline between
the levels of high tide and low tide
...
Can occur in a variety of areas, from rocky
coastlines to sloping mudflats
...
Corals are tiny animals in a mutualistic relationship with algae; corals produce CO2, and
algae produce sugars
...
Corals live in colonies; their exoskeleton contributes to the structure of
reefs
...
Neritic zone: the ocean zone beyond the range of the lowest tidal
level and which extends to depths of about 200 m; generally a region of high productivity
...
Photic zone: the area of the neritic and oceanic zones that contains sufficient light for
photosynthesis by algae
...
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...
People who place intrinsic value on biodiversity feel
religious, moral, or ethical obligations to preserve the world’s species
...

Instrumental value of biodiversity: a focus on the economic value a species can provide (e
...
,
the value of lumber and crops)
...
Benefits of diversity are estimated at $319 billion
per year in the United States, and globally at $3 trillion to $54 trillion per year
...
Regulating services: Benefits of biodiversity that include climate regulation, flood
control, and water pollution
...
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...
Supporting services: benefits of
biodiversity that allow ecosystems to exist (e
...
, primary production, soil formation, and
nutrient cycling)
...
Some extinctions are natural; some are caused by
humans
...

Explanations for extinctions include climate change following glacial retreat, human hunting
pressure, and epidemic diseases carried by domesticated animals
...
Declines can reduce the probability that a
population is able to survive changing conditions (e
...
, climate, emerging infectious diseases)
...
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...
Many livestock varieties have not been maintained; modern livestock
operations favor relatively few breeds
...
Reduced livestock genetic diversity provides less diversity
to us if we need to breed new varieties that can live in novel environments
Habitat loss - destruction and degradation of habitat has been the largest cause of declining
biodiversity
...

Overharvesting - Human technology has allowed us to harvest species at more rapid rates and
drive some species to extinction
...
Modern fishing techniques (long fishing lines, large nets, trawlers) have
increased the number of fish and shellfish caught
...
Collapsed fisheries occur in more than 25% of species assessed off the coast of the
northeastern United State
...
Only about 5% of introduced
species become established in a new region, but those that do have a variety of effects

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