survival of organism: depends on their ability to respond to changes in the environment
- responses to changes can be behavioral or physiological
stimulus: change in the environment that triggers a response
behavioral response: refers to how animals cope or deal with changes in their environment by changing their behavior
physiological response: refers to how animals cope or deal with changes in their environment by changing their physiological processes/habits
example:
- stimulus: extension of day length
- behavioral response: many bird populations tend to migrate elsewhere
- physiological response: some animals slow their metabolism to conserve energy
stimulus can be communicated between organisms to trigger changes in behavior with other organisms; they can communicate with:
- audible signals: birds use audible signals to send warnings to other birds or to attract mates; some primates use vocalization to assert dominance or warn of the presence of predators
- chemical signals (pheromones): can be released by some organisms to illicit a response in other organisms; responses can be mating, warning others, to scare off predators, etc.
- electrical signals: sharks and rays can send electrical signals throughout the water to locate prey species
- tactile signals: touching between primates can be used to express affection or to indicate dominance; some plants curl up to protect sensitive parts of their bodies from damage
- visual signals: some species use warning coloration to scare off predators
- aposematism: the use of warning coloration to inform potential predators that an animal is poisonous, venomous, or otherwise dangerous
signals can be used to establish hierarchy, find mates, and find resources
- natural selection will favor signals and responses that increase survival and the chance of successful reproduction; over time this can lead to evolution of the population
cooperative behaviors: can lead to increased fitness of individuals and populations; it is cooperative if it is beneficial to another organism, the recipient, and is selected, at least partially, due to the benefits to the recipient
- example: meerkats take care of each other; they huddle together for warmth, groom each other, forage together, fend off predators together in groups, etc.

Energy Flow Through Ecosystems

organisms use energy to reproduce, grow, and maintain organization; different species have different adaptations for maintaining energy levels (and body temps.)
endotherms: use thermal energy generated from their metabolism to maintain body temp. (ex. mammals, birds)
ectotherms: do not have internal mechanisms for maintaining body temp.; absorb heat from the environment; their behaviors will change depending on their body temp. (ex. fish, reptiles, amphibians)
metabolic rate: the total amount of energy an organism uses per unit of time
- smaller organisms: higher metabolic rate because they have greater SA:V ratios and lose heat more quickly; higher metabolic rates compensate for the quicker loss of heat
- larger organisms: lower metabolic rate because they lose heat less quickly
net energy gain: can result in energy storage (ex. fat tissues of animals)
net energy loss: can result in loss of mass or death of organism
changes in energy availability can affect population sizes (less energy = smaller population supported)
trophic levels: represent steps in the food and energy transfers between organisms in an ecosystem
- organisms are classified into trophic levels based on their food and energy sources
food chains: show the transfer of energy between trophic levels; direction of arrows in food chain show direction of energy flow between organisms
food webs: show the interconnections between organisms in different food chains; provide a more complete representation of energy transfers in ecosystems
- autotroph (producers): get energy from physical or chemical sources in the environment
- photoautotrophs: get energy from sunlight (ex. plants)
- chemoautotrophs: obtain energy from small inorganic molecules (ex. bacteria)
- heterotroph: get energy from carbon compounds made by other organisms; obtain energy from carbs, lipids, or proteins by breaking down the macromolecules using hydrolysis (ex. animals)
- decomposers: break down dead organic material to allow for the recycling of nutrients in the ecosystem (ex. fungi)
- detritivores: organisms that obtain energy by consuming organic waste of dead plants/animals (ex. earthworm)
kleptoplasty: an unusual strategy for obtaining energy; when a heterotroph consumes an autotroph that it uses as a food source but then removes the chloroplasts from the autotroph’s cells to incorporate them into their own cells
energy is lost as it moves through trophic levels; it can be lost as heat or being consumed for necessary metabolic processes in organisms
- more energy is required but harder to obtain in higher trophic levels, resulting in a smaller population (ex. there are less bears (top level) than there are bacteria (bottom level))
- biomass: the total quantity or weight of organisms in a given area or volume.; increases as you go down trophic levels (producers have greatest biomass)

Regulation in Ecosystems

bottom-up regulation: in which the population size of producers decreases, so the population of subsequent (higher) trophic levels also decreases
top-down regulation: when animals at higher trophic levels limit population sizes at lower levels
- if the predators (top level) are removed, the trophic levels in between predators and producers could increase due the lack of population control of them
availability of food and energy resources affects organisms’ reproductive strategies
- organisms in unstable environments: produce a larger number of offspring to increase chance of survival
- organisms in stable environments: produce fewer offspring because likelihood of survival is increased

Population Ecology, Community Ecology, and Biodiversity

Population Ecology

population: made up of individual organisms that interact with one another and with their environment in complex ways
- population sizes and population growth are affected by how organisms obtain the energy and matter they need to survive
- population growth depends on:
- population size (N)
- birth rate (B)
- death rate (D)
population growth rates are calculated as the change in population size over the change in population time: dN / dt
- calculating population growth can be with: dN / dt = B - D
- if birth rate exceeds death rate, population size will increase
- if birth rate is less than death rate, population size will decrease
- exponential growth: if there are no limiting factors (ex. abundance of food) on a population, it will experience exponential growth and can be described with the following equation:
- N: population size
- rmax: maximum per capita growth rate of the population
- the larger the population size, the higher the growth rate and the faster it will grow
some populations eventually exceed the resources of their environment, meaning the growth is limited by resource availability
- density-dependent factors: disease, predation, competition (for food, habitat, mates, etc.)
- density-independent factors: temp., precipitation, natural disasters
- both result in logistic growth of population, with the following equation
- - N: population size
  - rmax: maximum per capita growth rate of population
  - K: carrying capacity of environment
  - carrying capacity: the maximum population that can be supported by the available resources
  - as population size increases (N gets closer to K), the rate of population growth decreases

K-Selected vs. r-Selected Populations

K-selected: possess relatively stable population sizes at or near the carrying capacity of the environment
- k-selected populations usually reproduce more than once per lifetime, with few offspring per reproductive cycle
- invest greater levels of parental care in their offspring, resulting in higher survival rates of offspring
- usually experience logistic growth and are sensitive to density-dependent factors
- examples: most mammals, birds
r-selected: live in unstable environments
- usually reproduce at a younger age and only once per lifetime with large numbers of offspring
- invest less time in offspring, resulting in lower rate of survival for offspring
- experience “boom or bust” periods, in which periods of exponential growth lead to populations that far exceed the carrying capacity (“boom”), resulting in rapid decreases of population ('“bust”)
- usually not sensitive to density-dependent factors
- examples: many fish, amphibians

Community Ecology and Simpson’s Diversity Index

community: a group of interacting populations living in the same habitat; described by their species composition and species diversity
- species composition: number of species in a given area
- species diversity: reflects the number of species in an area and the number of members in each of those species
- species diversity gives a more accurate assessment of the variety of organisms found in an area
simpson’s diversity index: way of representing species diversity with the following equation:
- n: total number of organisms of a particular species
- N: total number of organisms of all the species
- the higher the SDI, the more diverse the community

Relationships Within Communities

interactions can change over time
- changing interactions can influence how many members of the community access the matter and energy they need to survive
competition: organisms compete for resources (ex. food, habitats, mates)
- interspecies competition: between members of two different species
- intraspecies competition: between members of the same species
- any competition can lead to the demise of an organism in an ecosystem
predator/prey: predator species eat prey species and depend upon prey populations for food
- insufficient numbers of prey species will lead to a decline in the predator species
- increasing number of prey species will lead to an increase in predator species
- fluctuation in the number of predators will generally follow fluctuations in the number of species
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niche partitioning: competing species may coexist if they use the resources available in their habitats differently
- dietary partitioning: where organisms eat different prey/sources of food, so they can co-exist peacefully
trophic cascades: refers to the far-reaching effects of the reduction of one trophic level in a food web
- example: decrease in sea otters lead to an increase in sea urchins because sea otters eat sea urchins
parasitism: a symbiotic relationship where one species benefits from the relationship but the other is harmed; negative relationship
commensalism: one species benefits and the other species neither benefits nor is harmed by the relationship; neutral relationship
mutualism: both species benefit from the given relationship between them; positive relationship

Biodiversity

biodiversity: refers to the variety of living organisms in an ecosystem
- high biodiversity: increased resilience and more adaptable to changes in the environment
- low biodiversity: less resilience and cannot adapt as well to changing environments
biodiversity depends on abiotic and biotic factors:
- abiotic: non-living factors; influence the types and the number of species that can survive in the environment
- ex. climate, water availability, etc.
- biotic factors: living factors; limit how many consumers can survive in the environment
- ex. number of producers
biodiversity of an ecosystem will influence the structure of food chains and food webs found in that ecosystem
keystone species: have a disproportionately large effect on an ecosystem compared to their population size
- when a keystone species is removed from the environment, the ecosystem may collapse

Disruptions to Biodiversity

invasive species: a type of disruption to the ecosystem; a non-native species that causes struggle within the populations of the native species (ex. increases competition, introduces disease, etc.)
human impacts:
- habitat destruction (as urbanization increases)
- diseases (humans can come in contact with new species and pass off pathogens to them)
- pollution
geological events: natural disasters (ex. volcanic eruption, flood) can decrease plant and animal diversity; prolong droughts can change biodiversity
disruptions in ecosystems can lead to evolution in populations
- changed environments will select for adaptations that provide advantages in the environment
- adaptations are generate by mutations, which are random, but selection for them is not random
rapid changes in environments can accelerate the pace of evolution