LIFESCI 7B Lecture Notes - Lecture 8: Ernst Haeckel, Population Ecology, Microbiota
10 Jun 2018
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Week 8
Video notes: Ecology--what is it anyway?
● Word ecology invented in 1869 by Ernst Haeckel from Greek oikos (house/household)+logia (study of,
knowledge)=oekologia→ household knowledge?
● Ecology: The scientific study of the interactions that determine the distribution and abundance of
organisms
○ Interactions in ecology
■ Biotic interactions: among organisms;
■ Abiotic interactions: between organisms and their non-living environment
○ Distribuion of organisms
■ Why are populations found where they are and not elsewhere?
■ Geographical, altitudinal, spatial distribution
○ Abundance of organisms
■ Why do populations grow or shrink? Stay constant? or go through cycles?
■ E.g. predator-prey cycles’
● Ecological systems: made up of organisms plus the external environment with which they interact
(biotic and abiotic components of environment)
○ Haeckel’s “house” meant “the total relations of the animal both to its inorganic and organic
environment”
○ Ecology is the study of “all those complex interrelations referred to by Darwin as the ‘conditions
for the struggle for existence’.”
■ → ecological interactions (within and between species) drive natural selection
● Ecology describes systems at a hiearchy of levels
○ Organism--the basic uit of ecology: an individual plant, animal, or microbe that exhibits
behavior, physiology, and life history (e.g. single prarie dog)
○ Population-- group of individuals of the same species that live, interact, and interbreed in a
particular area at the same time (e.g. group of prarie dogs in a field)
○ Community-- assemblage of interacting populations of different species in a particular area
(prarie dogs, hawks, plants, in a field)
○ Ecosystem-- the full community plus its abiotic environment (community+ the field)
○ Biosphere-- all the organisms and environments of the planet (the entire world’s ecosystems)
● Where do we find ecology?
○ Not just natural systems! → can occur wherever life is found including highly disturbed habitats
(e.g. plants growing through sidewalk cracks, agriculture, etc)--nature is all around us!
■ -even in mouths, hospitals, etc. (microbial community)
■ Microbiome: community of microorganisms that live on and in us
VIDEO NOTES: Ecology--How do we study it?
● Natural history: observation of nature outside of a formal, hypothesis-testing investigation-- provides
important knowledge on ecosystems
● Structured observations: track changes through time and detect correlations among outcomes and
possible causes
● Field observations are often the source of new questions and hypotheses and aid in design and
ecological experiments
● Ecological experiment: scientific study designed to test a hypothesis usually by manipulating the
system
○ E.g. exclosures, food supplementation
find more resources at oneclass.com
find more resources at oneclass.com
● Natural experiment: when a natural process perturbs the ecosystem dramatically, so ecologists can
learn by watching how the ecosystem responds
○ E.g. observing effects volcano eruption, flood, epidemic
● Mathematical models and computer models: important tools in the study of ecosystems
○ Simplefied versions of real ssytems, based on knowledge of natural history
○ Essential tools for:
■ Situations where experiments are impossible
■ Testing mechanisms behind observed patterns
■ Looking for GENERAL PRINCIPLES
● Looking for big picture/underlying truths that govern ecology
● Many multidisciplinary approaches
○ Molecular ecology uses genetic sequence information to study ecology of subject organisms
○ Stable isotope ecology looks for isotope signatures from different kinds of food in an animal’s
tissue, to learn from what it has been eating
○ Chemical ecology studies how organisms use special chemicals for defense against predators,
mate attraction, and other functions
○ And many more
● Take advantage of technology
○ Use of CAT scan to observe fungal activity in tree
○ Sensors, satellite imagery, GPS collars, etc
● Citizen science:
○ Because natural world is so vast (too much for one person to study) and fascinating (many
interested). Citizens can play a role in generating useful scientific data
■ E.g. group of people get together annually and count christmas birds
VIDEO NOTES: Population Ecology
● Population: all the individuals of a species that interact with one another within a given area at a
particular time
○ Why study populations?
■ To increase populations of beneficial species that provide resources/food
■ To conserve species for ethical and aesthetic reasons
■ To decrease abundance of crop pests, pathogens etc.
■ Interest in human population levels
● Populations vary in space and time
○ Abundance varies on several spatial scales
■ Geographic range--region in which species is found
● Within the range, species may be restricted to specific environments or habitats
■ Habitat patches are islands of suitable habitat separated by areas of unsuitable
habitat (environmental abiotic components→ plants found→ organisms found)
○ Population densities are dynamic, changing over time
■ Can change due to environmental fluctuations (good years and bad years!)
■ Density of one speies population may be related to other species population (e.g.
predator-prey relationships)
■ Change in population size depends on number of births and deaths over given time
● “Birth-death” or BD model of population change
○
■ B=# of births, D=number of deaths; Nt=total population in one
year, Nt+1=total population in the next year
find more resources at oneclass.com
find more resources at oneclass.com
● To calculate population growth rate (how much the population size changes
per unit of time; = B - D
○
● Per capita rates are the number of events per individual, per unit of time
○ → calculate by dividing # of events by population size
○ Per capita birth rate (b)--number of offspring produced by an average
individual (so b=B/N)
○ Per capita death rate (d)--chance of dying for an average (female)
individual (d=D/N) (total deaths/individuals who could die)
○ Per capita growth rate (r)=(b-d)= average individual’s contribution to total
population growth rate
■
■ If b>d, then r>0, and population grows
■ If b<d, then r<0, and population shrinks
■ If b=d, then r=0, and population size does not change
VIDEO NOTES: Life Histories and Life Tables
● Life history of a species describes time course of essential events during an average individual’s life
○ Growth and development, dispersal, reproduction, death (similar to life cycle?)
○ Every species can be characterized by life history depending on important events throughout
lifespan
● Life table: shows ages at which individuals make important life cycle transitions and how many
individuals do so successfully; 2 crucial types of information given from life tables
○ Survivorship: fraction of individuals survive from birth to each individual stage/age
■ Culmulative: how many are stilll alive compared to the original population?
■ Per capita death rates= total deaths/total who could die
● Divide by number of individuals that COULD have died (not original starting pop)
i.e. the # alive at the beginning of the specific time period
○ Fecundity: birth rate: average number of offspring each individual produces at a given life
stage/age
■ Year-by-year; avg number of live young at EACH stage/age
○ Encapsulates life history/demographic history of individuals of that cohort (group born in specific
year/time period, etc))
■ Observing fecundity changes and survivorship curves chage throughout life span
■ Fecundity: per capita birth rate of given year
■ Survivorship: think of each cohort have 100 individuals: tracking year after year how
many are left and how many have died
● Can calculate per capita birth rate and death rate
● Life histories vary among species,
○ How many different stages, types of stages, ages of reproduction and frequency of
reproduction, how many offspring, life span, etc.
● Can vary within a species
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Ecology: the scientific study of the interactions that determine the distribution and abundance of organisms. Abiotic interactions: between organisms and their non-living environment. Ecological systems: made up of organisms plus the external environment with which they interact (biotic and abiotic components of environment) Haeckel"s house meant the total relations of the animal both to its inorganic and organic. Ecology is the study of all those complex interrelations referred to by darwin as the conditions environment for the struggle for existence". Ecological interactions (within and between species) drive natural selection. Ecology describes systems at a hiearchy of levels. Organism--the basic uit of ecology: an individual plant, animal, or microbe that exhibits behavior, physiology, and life history (e. g. single prarie dog) Population-- group of individuals of the same species that live, interact, and interbreed in a particular area at the same time (e. g. group of prarie dogs in a field)
