unit 4: BIO 311D

ecology

the scientific study of the interactions between organisms and the living/biotic and non-living/abiotic parts of their environment

these interactions determine the distribution of organisms and their abundance

Why Ecology?

• studying ecology helps us undertand the relationships between organisms and their environment, including how ecosystems function and how they are affected by human activities

• humans are part of the global ecosystem and our everyday decisions can positively or negatively, directly or indirectly, impact all the other levels of life

• can implement practices and policies to conserve and restore ecosystems for future generations

tolerance for abiotic conditions

species have a range of tolerance for abiotic conditions; sunlight, water, pH. nutrient availablity, this limits where they can live

abiotic factors

influences species distribution

• ecological factors

  • red kangaroos are adapted to arid areas

  • cannot tolerate cold or wet areas

  • drink less water than most other kangaroos, urine is more concentrated to conserve water

• history and dispersal

  • geographic isolation- only in Australia

  • land bound, cannot disperse due to continential drift

biotic factor

influence species distribution

• giant kelp normally thrive in the waters along California’s coast

• long-spined sea urchin eats the kelp

• when sea-urchin removed, kelp growth occurs

• sea otters are keystone species that eat the urchins and this helps the kelp thrive

• climate change has caused an increase in urchin population, loss of otters, 95% of kelp forests have been destroyed

keystone species

disproportionately big impact relative to their abundance

population

a group of individuals of a single species living in the same general area

three ways to describe populations

1. number- count the number of individuals

2. density- estimate the number of individuals in a given area, quadrant sampling, marked

3. dispersion- spatial arrangement of individuals, clumped, uniformed, random

• depends on environmental conditions and biological needs

Three patterns of dispersion

clumped, uniform, random

clumped dispersion

most common pattern of population dispersion

• resources are patchy

• social behavior (hunting, predator defense, mating/paternal care

uniform dispersion

organisms are fairly evenly spaced over the area they occupy

• species with aggressive, territorial interactions

• try to avoid contact, compete for a scarce environmental resource

random dispersion

organisms have an unpredictable distribution

• species that do not interact strongly

• ex. wind-blown dandelion seeds

population size is the result of 2 processes

birth/ immigration- add individuals to the population

death/ emmigration- remove individuals from the population

change in population size =

(birth + immigrants) - (death + emmigrants)

change in population size for a closed population =

births - deaths

population growth rate

model population growth rate

births = deaths, R = 0

births > deaths, positive growth

births < deaths, negative growth

r

growth per individual and we multiply by N to get total growth R, tells you how fast individuals are reproducing

R

how much the entire population changes, tells you how fast the population is growing

exponential growth

• population increase under idealized conditions, resources are unlimited

• rare in the living world

• when introduced species where they have no natural predators to limit growth

• cannot be sustained for long

• j-shaped curve

equation of exponential growth

example of exponential growth

elephant population grew exponentially after hunting was banned in Kruger National Park, South Africa

• caused damage to food supply

• birth control and elephants exported

carrying capacity (K)

the maximum population size the environment can support

• varies depending on the resources available at any partiicular time

• not a constant number so population growth is dynamic

what limits population growth in real ecosystems?

food, space, disease

logistic population growth model

the growth rate declines as carrying capacity is reached

• equation starts with the exponential model and adds an expression that reduces per capitia rate of incease as N approaches K

• s- shaped curve in graph

• limits growth by including carrying capacity

logistic growth equation

what happens to birth rates and death rates as you approach K?

birth rate decreases and death rate increases

[(K-N)/K]

the fraction of K that is available for population growth

N<<K, similar to exponential growth, close to 1

N~K, close to 0

N = K, population stops growing. = 0

Where is r greatest on the graph, where is the point of maximum growth?

steepest slope

why do some populations overshoot K before settling down to a relatively stable density?

negative feedback, there are time lags for death rates to kick in and reproduction to slow down

density dependent factors

influenced by the relative size of a population

mostly biotic factors

• competition for limitied resources

• predators

• availability for resources

• nutrient supply

• disease spread

• accumulation of wastes

when these factors work the birth rates fall and death rates rise with > population density

• keeps the population growth close to K

example of density dependent population regulation

a snowshoe hares chane of dying depends on how many lynx are present

density independent factors

not influenced by the relative size of a population

mostly abiotic parts

• abiotic factors- temperature, CO2 levels

• natural disasters

• weather conditions

the birth rate and death rate do not change with population density

why did the human population increase relatively slowly until 1650 then begna to grow exponentially?

advances in agriculture and the industrial revolution decreased death rates and increased life expectancy

although human population is still growing, why did population growth began to slow during the 1960s?

innovation can increase K, but there are environmental limits, the carrying capacity for humans is unknown

community

a group of populations of different species living together and interacting with each other

trophic structure

a community can be organized by who feeds whom

producers

obtain atoms and energy and convert then into essential carbon-based molecules of life

• make their own food

consumers

feed on producers and other consumers to survive

• must consume their food

decomposers

feed on dead organisms or waste to renew the raw materials for life

• break down decomposing organic matter

• key for health of ecosystems

who are decomposers in land based ecosystems?

fungi, earthworms, dung beatles and other recyclers

two main types of interactions

intraspecific and interspecifc

intraspecfic interactions

interactions between organisms within the same species

• competition for resources, mates, shelter

interspecfic interactions

interactions between organisms of different species

• competition

• predation

• herbivory

• parasitism

• mutualism

• commensalism

classification of community interactions

can have positive, negative, or nuetral

competition

(-/-) interaction

• when individuals of different species compete for a limited resource that limits the survival and reproduction of each species

  • weeds compete with garden plants

  • different animals trying to eat the same food source

competitive exclusion

• when two species compete for the same limiting resource and use it in the same way, they cannot coexist in the same place

• one species will used the resources better and the inferior competitor will be eliminated

competition for limited resources leads to

competitive exclusion

ecological niche

the specifc set of biotic and abiotic resources that an organism uses in its environment

• location of habitat

• activity patterns of the organism, time active

• resources its obtains from the environment

• interactions that occur with other species

• food, ran

two types of ecological niche

fundamental niche

the niche which could potentially be occupied

realized niche

the niche that is actually occupied, primarily due to competition

how to distinguish both niches

predation

(+/-) predator kills and eats other species

• species adapted ways to defend themselves

  • mechanical- thorns, shells, quills

  • chemical- toxins

  • behavorial- herding

coloration

• adaptation to defend aganist predators

• cryptic coloration- camouflage

• aposemetic coloration- bright warning coloration

herbivory

(+/-) herbivore eats parts of a plant or algae

parasitism

(+/-) parasite derives its nourishment from another organism, the host, which is harmed not usually killed in the process

• endoparasite- parasite live inside host, tapeworm

• ectoparasite- parasite live on their host, mosquitoes

mutualism

(+/+) both species benefit from relationship

• symbiosis- cannot live without eachother, only present in some

commensalism

(+/0) one of the species is benefited and the other is neither harmed or helped

food chain

simplistic linear sequence of organisms through which nutrients and energy move from one species to another

• each organism occupies a trophic level

• quaternary, teritary, secondary, primary, primary producers

apex predator

top level carnivore has no natural predators

food web

a complex web of interdependent feeding relationships within a community

• more representative of nature

• organisms can have more than one food source and predators

• species my play a role at more than one trophic level depending on the food chain

species diversity

increases in two parts

• species richness- number of different species in the community

• relative abundance- the proportion each species represents of all individuals in the community

biodiversity

extremely important for healthy ecosystem

• diverse communities

  • have higher levels of primary production- energy

  • are better able to withstand or recover from disturbances

  • more resistant to invasive species

invasive species

organisms that become established outside their native range

• become dominant because they lack natural enemies, can negatively impact the native biodiversity

• outcompete natives for food and space, reshaping the ecosystem

foundation species

dominant species that are the most abundant or that collectively have the highest biomass

• strong effects on communities as a result of their number or size

  • loss can allow other species to take over ______

keystone species

presence is key to maintaining biodiversity within an ecosystem and upholding its structure

• unrelated to abundance in a community

ecosystem engineers

species that dramatically alter their physical environment

• some foundatio species can be ecosystem engineers- trees

• ex. beavers create dams- new habitats for organisms

two models of community organization

bottom-up model- a unidirectional influence from lower to higher trophic levels

• altering biomass at lower levels will cause changes through the food web

top-down model- a unidirectional influence from higher to lower trophic levels

• altering biomass at higher levels will cause changes through to food web

• move in alternating +/- effects

disturbance

an event, such as a storm, fire, flood, drought, or human activity, that changes a community by removing organisms from it or altering resource availability

• most communities are constantly changing after disturbance

intermediate disturbance hypothesis

moderate levels of disturbance foster greater species diversity than do high or low levels of disturbance

• too much disturbance wipes everything out

• with too little disturbance, the dominant species take over and outcompetes other species

ecological succession

a disturbed area my be colonized by a variety of species, which are replaced by other species, which are replaced by still other species

primary succession

recovery/colonization in an area that is virtually lifeless- bare rock

• soil has not yet formed

• prokaryotes, protists, lichens, and mosses- pioneers, colonize first and creat organic matter and soil for species to grow

secondary succesion

occurs when an existing community has been cleared by a disturbance that leaves the soil intact