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BIO 225: ACT III

Ecology

• Ecology: the study of – Drivers of biodiversity – Drivers of a species’ distribution – Drivers of a species’ abundance

• Environmental science: – The study of the impact of humans on the

environment – Emphasis on air and water quality

• Conservation Biology: – The study of imperiled species and habitats

• Animal Rights, Environmentalism, Plant Rights

• People were doing ecology before there was ecology

• Understanding the abundance of organisms and their distributions is how our species survives!

• Comes from “oekologie” coined by German scientist Ernst Haeckel (oikos = house)

• Became ecology in 1893

Ecology

• Aristotle Historia Animalium – Descriptions of animals and plants

– Described plagues and the environment as a control

• Greek physician, Pedanios Dioscorides (active AD 60s–70s) – De Materia Medica

– Identification and natural history of medically important plants

• Romans – More practical: wrote on agriculture

Ecology: Post-Classic to Pre-Enlightenment

• Mostly descriptive

• Study of plants was mostly related to medicine

• Andreas Vesalius’ De fabrica humanis (1543)

– One of the first books showing dissected humans and animals

• Conrad Gessner (Swiss) 1555 Historiae animalium

– Wrote on the natural history of animals

Ecology: Demographics

• Many early scientists were interested in estimating human populations and trends

• John Graunt (1620–1674), who also held several city offices, published Natural and Political Observations Mentioned in a following Index, and Made upon the Bills of Mortality: with Reference to the Government, Religion, Trade, Growth, Ayre, Diseases, and the several Changes of the said City.

– Outlined the important aspects of demography: births, deaths, sex ratios, age structure

– Referred to wild animals

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Ecology: the small stuff

• Robert Hooke (1635–1703)

• Micrographia

– Plant cells, microorganisms

• Inventor

– barometer, thermometer, hygroscope, rain gauge, and wind gauge

Geography

• Alexander von Humboldt (1769–1859)

• I shall try to find out how the forces of nature interact upon one another and how the geographic environment influences plant and animal life. In other words, I must find out about the unity of nature

• World traveler

• Noted the relationship between climate and the limits of distributions

• Inspired Darwin (and many others)

Enter Darwin

• Natural selection

• Phylogeography

• Climate

• Pollination

• Earthworms

• Dispersal

Population Biology

• Essential to understand human populations

• Essential to understand endangered species

• Essential to understand pests

• Essential to understand other economically important species

Defining the individual

• Unitary – Individuals are discrete

– Less plasticity

• Modular – Individuals reproduce by modules

– More plasticity

– Ramets and genets

– Biomass

• Growth – Determinate

• mammals, some plants [mostly herbs])\

– Indeterminate • Reptiles, most plants

Terms

• Distribution • Range • Territory • Abundance • Density • Population • Metapopulations • Dispersion • Dispersal

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Biogeography

• Why are organisms found in some areas and not in others?

– Organisms have histories

– Organisms vary in their ability to disperse

– Organisms vary in their environmental tolerances

Plate Tectonics

• http://www.tectonics.caltech.edu/outreach/animations/anim_pangaea/Resources/anim_pangaea.mov

Species level: Helmeted Hornbill Family level: Hornbills

Order level: Coraciiformes Habitat suitability

• Abiotic factors

– Temperature, precip, pH, O2, salinity

• Biotic factors

– Predators, prey, parasites, disease, competitors

• Abiotic x biotic

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Density and Dispersion

Densities vary across range

• Breeding bird survey maps

• In general, species reach their highest densities in the center of the range

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Spatial Resolution and Distributions (see Fig 8.15)

Populations

• Number of individuals

– All individuals (N)

– Sample (n)

– Within a natural boundary

• Islands

• Well defined habitats (e.g., pond)

– Within an arbitrary boundary

• State, region, county

Populations

N is very rarely ever known • except for the very rare! • or very obvious in well-defined boundaries •too rare? extinct?

Snowdonia hawkweed from the beautiful nation of Wales. N=1

Population Indices

• Population Index

– Not all organisms are counted

– Some standard is chosen then changes indicate population changes

– Common in wildlife management

– Example

• deer brought into check stations indicate the population when the number of deer out there are never known

Population Indices

• Population Indices

– Minimal work (therefore cheap)

– Minimal information • Difficult to predict the consequences of management decisions

• Adaptive management

• Difficult to predict the consequences of environmental changes

– Climate change

– Introduced species (parasites, disease [West Nile], new food, predators, competitors)

Population Estimation

• Population estimation attempts to figure out how many individuals there are in an area – N can refer to all individuals of a species but more often the total

number of individuals in an area

– A sample of a population is n and can be used to estimate N

– Formally, n = (N hat)

– N is hardly ever known

– A good estimate is when

N̂

NN ˆ

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Population Estimates

• How do we get ?

• Plants

– Sample in a small area to get density then extrapolate

– Density = number of individuals/area

• Animals

– Capture-recapture

N̂

Capture-Recapture

• Animals are captured, marked, released, and then resampled

• Labor intensive (not cheap)

• Lots of assumptions – Animals don’t avoid trapping

– Many more but…

• Lots of information – Survivorship, sex ratios, recruitment, health, DNA

samples, etc

Capture – Recapture

• Many animals are PIT tagged – Passive Integrated Transponder

– used in livestock and pets as well as wildlife

• Mammals get ear tagged

• Birds get banded

• Animals with complex patterns can be photographed – Whales, jaguars, some salamanders

• Insects and hummingbirds – white out!

Capture – recapture

• 2 sample

)2()1(

)(1)((

1

)1)((ˆ2

secsecsec

recapturedrecaptured

recapturednnn

recaptured

nnN ondondinitialondinitial

Spatial Scale: Extent Spatial Scale: Resolution

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Geographic Range Population Growth and Regulation

• Examples – Giant puffball

• produces 7 trillion spores/individual

• If all lived and each produced 7 trillion spores each

• The mass of puffballs = mass of Earth

– European Starling • 1890 ~ 160 released in Central Park, presently 170

million

– African Elephant • 1 pair will become 19 million in 700 years

Life table analysis

• Types – Cohort/Longitudinal

• Organisms (including people) are followed from start to finish

• Difficult in long-lived organisms

• Important in epidemiology

– Static • Organisms of all ages are studied at once

• Vital rates (births and deaths) are assumed to be constant

Vital rates and life tables

• Closed population

– Birth, death, sex ratios, age structure

• Open Population

– Closed population vital rates + emigration and immigration

• Vital rates are estimated from life table analysis

• Life tables

– Cohort (longitudinal)

– Static (cross sectional)

Life Table

• Requires

– Age or stage

– Number of births for each age or stage

– Number alive at each age or stage

• You calculate

– EVERYTHING!

– Survival rates and fecundity rates

Elements of a life table

• Survival rate (Sx):

– probability of surviving to the next age/stage (Nx+1/Nx)

• Survivorship (lx) :

– proportion of original cohort surviving to time x (Nx/N0)

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Elements of a life table extended

• Life expectancy – Lx = (lx + lx+1)/2

– Tx = SUM(Lx)*Age span for category x

• Death rate (dx) = lx - lx+1

• Age specific mortality rate (qx) = dx/lx

• mx = Fx/nx

• Age specific fecundity rate fx = mxlx

• Basic reproductive rate R0 = SUM mxlx

Life Table

Life Table Basic Reproductive Rate

Survivorship Curves Fecundity

• Semelparous

• Iteroparity

– Iteroparity and age

– Iteroparity and size

– Iteroparity and resources

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Fecundity and age Age class and sex ratios

Lambda and r

• Both refer to growth rates

• Use λ when reproduction is pulsed/seasonal

• Use r when reproduction in continuous

• Note that or r=?

t

t

N

N 1

N

dt

dN

r

re

Population Growth

• Note the direction and shape of the curves

• Pulsed breeding

– Changing starting population

– Changing lambda

• Continuous breeding

– Changing starting population

– Changing r

Doubling time

• Is the time it takes for a population to double

• Human population growth rate is 1.18%. What is the doubling time?

rtd

2ln

So far no stopping populations

• Our models have populations increasing to infinity (and beyond)

• Realistic?

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Population Regulation

• Limiting factor – The resource that, if increased, would result in a

population increase

• Density-independent factors – Climate

• Density-dependent factors – Disease – Food – Competition

• Mates • Resources • Breeding sites

Carrying capacity

• Maximum population a habitat can sustain

• Represented with K

• In rare cases, K is a constant

– Breeding site limitation

– Space availability for sessile organisms

• More likely that K changes over time

Fecundity and Density Population growth

0NN t

t

rt

t eNN 0

Logistic Growth

• Growth rates

• Population size

K

NKrN

dt

dN

rt

t

eN

NK

KN

0

01

Logistic Growth

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Logistic Growth Human Populations

Human Populations

• 7 billion

• http://www.census.gov/main/www/popclock.html

Population Dynamics

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Population Dynamics

• Populations differ in their dynamics over time

– Some populations are relatively stable

– Some populations vary

– Some populations are highly variable

Mallards in North America

Greater Prairie Chicken Role of competition in phytoplankton population for the occurrence and control of plankton bloom in the presence of environmental fluctuations. Ecological Modeling.

Rodent and predator population dynamics in an eruptive system. Ecological Modeling. 142.

Delayed Density Dependence

• Fig 10.10

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Predator-prey oscillations

• Figure 10.9

Extinctions

• Small populations at greater risk of extinction

– Inbreeding

– Demographic stochasticity

– Environmental stochasticity

– Castastrophes

– Allee effect

Extinction-Colonization

• On the smallest scale, individuals die and offspring may take their place

• Small populations in habitat patches may go extinct

• The patch can be recolonized through dispersal

• These subpopulations are called metapopulations

Habitat Fragmentation

• Patchiness of habitat is normal

• Metapopulations are sustained by dispersal

• If dispersal to patches is reduced then local extinction will occur

• Habitat fragmentation reduces dispersal

Habitat Fragmentation Habitat Fragmentation

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