Ecology

• The study of how organisms interact with each other and their environment

Key Elements of the Environment

• Temperature – most organisms require a narrow range (humans excluded)

• Water – very important, much more diversity in rainforest than in desert

• Sunlight – where almost all energy originates from

• Soil – pH, minerals, nitrogen, phosphorus affect the ability of plants to grow

Population properties• Population size – number of individuals• Population density – number of individuals in a

given unit– Los Angeles – 7544 people/square mile– South Sioux City, NE – 2725 people/square mile– Manila, Philippines – 111,576 people/square mile– New York City – 27,012 people/square mile

• Population dispersionclumped uniform random

Population growth• Population at current time = population from

past time + births during that time – deaths during that time + immigration – emigration– Simulation of population growth – start off with

10 people (5 couples) – each couple has 4 kids• How many offspring? - 20• 20 children become adults and each couple has 4 kids• How many offspring? – 40• Doubles each generation – so let’s draw a graph

Population growth• Exponential growth – the larger

the population, the more it will grow

• Eventually this has to stop– Space– Availability of resources

• Carrying capacity – the max population

• This type of growth is called logistic growth (sometimes called a sigmoid curve)

Factors that influence population density

• Density-independent events– Severe weather (floods, drought, etc.)– Severe geological disturbances (volcanoes,

earthquakes, etc.)

• Density-dependent events– Aggressive behaviors (defending territory)– Emigration

Maximizing population productivity• Demand for fish has increased due to general health benefits and increase in

global population• Overharvesting has caused population decline in wild salmon• Salmon farms have helped alleviate the problems of overharvesting• Farms have negative health and ecological impact

– Toxins in fish– Fish lice and viruses are becoming common if farmed salmon, which are passing

them on to wild salmon

overharvesting Wasting resources

Maximum sustainable yield

Demography• The study of populations using statistics• Cohort – A group of individuals that are the

same age• Fecundity – Number of offspring produced in

a standard time (for example, a year)• Mortality – The number of individuals that die

in that time• Proportion of males to females is called the

sex ratio

Survivorship curve• Type I – Most live a long

time, then suddenly die• Type II – constantly die

off• Type III – many die off

young, the ones that survive live for quite some time

Community and Ecosystem• Community - all the species in a given area• Ecosystem – all the species and all the non-

living components in a given area

The Niche and Competition

• Niche – all the ways in which an organism uses its habitat

• Habitat – the place where an organism lives• Competition – when two organisms attempt

to use the same resource– Interspecific – between two different species– Intraspecific – between the same species

Fundamental Niche vs. Realized Niche

Fundamental Niche – where a given species is ABLE to liveRealized Niche – where a given species actually lives because of competition

Competition• Competitive exclusion - If two species are competing for the same

resource, the one that uses it more efficiently will out grow the other

Time

Popu

latio

n

P. Bursaria grown separately

• No two species can occupy the same niche if resources are limited. If two species coexist…• Resources are not limited• They do not occupy the same niche

Resource partitioning• Competition between two species is rare in

nature because of 2 reasons:– One would outcompete OR– A new niche would be formed by dividing up

resources – resource partitioning• Sympatric – closely related species that divide up resources

– must live close to each other• Allopatric – closely related species that do not divide up

resources – so usually do not live close to one another• Allopatric species look more alike than sympatric species –

called character displacement

Character Displacement

• Character displacement is not the same as disruptive selection

Coevolution• Symbiosis – two organisms that live together

and whose existence is altered because of this relationship– Mutualism – both benefit– Commensalism – one benefits, other is unharmed– Parasitism – one benefits, other is harmed• Sometimes parasitism can be considered a predator-

prey relationship

Predator/Prey cycles

• Predation – the consuming of one organism by another– Predator – the one doing the eating– Prey – the one being eaten

Defense against predators• Plants– Thorns– Spikes– Prickles– Chemicals (pungent tastes usually associated with toxicity)– Many others

• Animals– Poisons– Warning coloration– Camouflage– Speed– Many others

Mimicry – a type of defense• Batesian mimicry – non-harmful organism mimics the look

of a harmful organism• Mullerian mimicry – similar pattern development between

harmful organisms• Self-mimicry – one body part looks like another body part

Batesian

poisonous Non-poisonous

venomous

MullerianMullerian

Ecological succession

• Succession – more complex communities replace simpler ones as time goes on– Primary Succession – occurs on a substrate that

never had life prior• Examples: volcanoes, rocks, lakes left by glaciers

– Secondary Succession – occurs on a substrate that had life prior, but was almost completely wiped out• Deforestation, flood, fire