Lecture 18 Ecology

• Ecology: the study of relationships and interactions among organisms and their environment

What’s involved? Predator-prey relationships Feeding relationshipsHabitats and niches Availability of nutrientsPollution and habitat degradation

• Ecosystem: a community and its abiotic (non-living) environment• Population: a group of organisms of the same species (capable of interbreeding)

that live in the same area at the same time• Community: a group of populations living and interacting with each other• Species: a group of organisms of similar appearance and which can interbreed to

produce viable offspring (offspring can live to maturity and produce their own offspring)

• Habitat: the physical area in which individuals of a certain species exist • Biosphere: the portion of the Earth and its atmosphere that can support life; the total

of all areas where living things are found, including the deep ocean and lower atmosphere

Organism

Population

Biosphere

Community

Ecosystem

Many organisms make up a population

Many populations make up a community

Many communities make up an ecosystem

Many ecosystems make up a biosphere

This is where abiotic factors

come into play!!!

• Autotroph/producer: an organism that makes organic molecules from inorganic molecules using light or chemical energy– “self-feeder”– Photoautotrophs: undergo photosynthesis; use light energy to convert inorganic

carbon (CO2) into organic compounds– Chemoautotrophs: break down inorganic chemicals by chemosynthesis to form

organic compounds– Examples: algae, some bacteria, plants

• Heterotroph/consumer: an organism which eats other organisms to obtain energy and organic moleculesExample - us

• Detritivore: an organism which ingests dead organic material– Examples: scavengers, earthworms

• Saprotroph/decomposer: an organism that feeds on dead organic matter using extracellular digestion– Specialized detritivores! – Consume cellulose (plant matter) and nitrogenous wastes (i.e. poop) – Examples: fungi and bacteria

Communities and

Ecosystems

• Food chain: a sequence of trophic relationships in which one population feeds on another .

• Trophic level: a step on a food chain or food web

4.1 Communities

and Ecosystems

• Food web: a diagram that shows all of the feeding relationships in a community

Energy pyramid

Fourth trophic level

Third trophic level

Second trophic level

First trophic level

Tertiary consumers

Secondary consumers

Primary consumers

Producers

Communities and Ecosystems

The Carbon Cycle

Lecture 19 Populations• Population size affected by

• Birth rate +

• Death rate -

• Immigration +

• Emigration -

Population Size

Immigration

Emigration

Birth Death

Populations

• Sigmoid growth curve involves– Exponential phase– Transitional phase– Plateau phase

Exponential

Transitional

Plateau

Populations• Exponential growth

– Unlimited – All organisms can rapidly increase their

population size if there are no factors controlling their growth

– Birth rate alone controls growth rate

Populations

• Transitional and plateau phases– The initial rapid increase in population size

slows down (transitional phase) until the rate of growth is zero (plateau phase)

– When r = 0, the number of individuals in the population has reached the carrying capacity—the maximum number of individuals of a species which can be sustainably supported by the environment

Populations

• Factors which limit population growth may be density-dependent or density-independent– Density-dependent factors

• Affect a larger proportion of the population as the density of individuals increases

• Examples: mortality due to predation or disease and intraspecific (within a species) competition

– Density-independent factors• Affect a proportion of the population regardless of its density• Example: mortality due to natural disasters (still, if the

population is denser, there will be a greater affect on the population size even though the proportion affected is independent of density)

Populations • Factors which limit population growth may be

extrinsic or intrinsic– Extrinsic population-limiting mechanisms

• Originate outside of the population and include biotic and physical factors

• Examples: food supply, predation, disease, weather

– Intrinsic population-limiting mechanisms• Originate in an organism’s anatomy, physiology, or behavior• Examples…

– Koalas may reabsorb a developing embryo when conditions are crowded and resources are limited

– Lemmings migrate in large groups when resources are depleted

– Competition for resources

Populations

• Ecologists often study a few individuals of a population in order to draw conclusions about the entire population

• Random sampling: a method used to ensure that every individual in a population has an equal chance of being selected for study– Quadrat sampling (useful for determining population

size of stationary organisms like plants) – Mark-Recapture method (useful for determining

population size of organisms that move around)

PopulationsQuadrat sampling for estimating population size

(a quadrat is a square area of known size)1. A quadrat is placed in the area to be sampled and

grid lines are marked within the transect and numbered

2. Two random numbers are selected as coordinates3. Individuals within the random square are counted

and the number is recorded4. Steps 2 and 3 are repeated as many times as

possible5. The total size of the sample area is measured6. The mean number of plants per quadrat is calculated7. The estimated population size is calculated using the

equation below

PopulationsMark-recapture method for estimating population size

1. Capture as many individuals as possible in the area to be studied2. Mark each captured individual (without making them more

camouflaged or more visible to predators—this would skew results!)

3. Release all marked individuals into habitat4. Recapture as many individuals as possible and count how many

are marked and how many are unmarked5. Calculate the estimated population size using the Lincoln index:

Estimated population size = (n1 * n2) / n3

where n1 = number initially caught and markedn2 = total number caught on second capture

n3 = number of marked individuals recaptured