ORGANISMS AND THE ENVIRONMENT (Ch 21 – Biogeographic Processes)
I. ENVIRONMENTAL FACTORS
- all things consumed by an organism
- consumption causes a decrease in supply of resources (less is available)
- plants need:
- animals need:
B. Environmental Factors
- abiotic environmental factors that influence organisms but are not consumed
- directly influences rates of physiological processes
- metabolic processes have a certain temperature range
- influences animal physiology and need for shelter
- indirectly influences the availability of/demand on resources
b. Light - Photoperiod
= seasonal changes in light that trigger life processes
- vegetation structure in exposed locations
2. Edaphic Factors = soil
- texture, structure, organic matter, organisms, acidity and alkalinity
3. Geomorphic Factors = landforms
- slope steepness = angle relative to horizontal
- slope aspect = orientation of the slope
- relief or slope position II. ENVIRONMENTAL FACTORS AND SPECIES DISTRIBUTION
A. Theory of Tolerance
- each and every species is able to exist and reproduce successfully only within a
definite range of values for a particular environmental factor
R = organisms grow and Reproduce successfully
G = organisms Grow but cannot reproduce
S = organisms Survive or persist but cannot grow
T = Tolerance range for that factor, beyond tolerance is lethal
O = Optimum level, at that level maximum performance
Note: there are both upper and lower limits of tolerance, beyond which the
B. Bioclimatic Frontiers
- climate factors interacting to determine the distributional limit of a species
- what climatic elements limit:
(a) ponderosa pine?
(b) sugar maple?
C. Ecological Niche
- Total structural and functional role of a species in the ecosystem
- characteristics of a species niche include combined tolerance ranges for all the
environmental factors that influence the species
- each factor can be considered as one niche dimension
- multidimensional - as many dimensions as factors that define the niche - factors also include biotic interactions:
1. Negative interactions (cost to one or both species)
2. Positive interactions (benefit one or both species)
D. Niche versus Habitat
- role of a species, "profession"
- Fundamental niche = potential distribution of the species with optimal conditions
- Realized niche = actual habitats where organism is found due to interactions
and limitations on resources – presence of competition.
- the actual place where the organisms lives, "address"
- characterized by a particular set of environmental factors that match the
Population - a group of organisms of the same species in a given place at the same time
- changes may occur between locations (spatial)
- changes in the number of individuals within a population (temporal)
A. Spatial Distribution
Recall from last class,
Habitat = area with particular set of environmental factors (abiotic and biotic) that
match the organism’s niche.
Range: space of distribution. Does not grow on top of the mountain.
Dispersal: ability to move from birth site to a new (another) site.
1. Ecological dispersal: occurs within a geographic range
-movement of a 'propagule' that can establish a new individual.
-examples: pollination (plants), eaten by animals (birds or flying insects), pieces of
2. Geographical dispersal: expansion of the range
3. jump dispersal: cattle egret = jump dispersal followed by diffusion in the Americas.
Reproduction and finding new habitat (diffuse). 4. Diffusion: looking for new habitat and settling in. Corridors = regions of similar climate
and vegetation structure that facilitate dispersal (ex: restoring and managing habitat
for reptile and amphibians. US Natural Resources Conservation Services).
Corridors = regions of similar climate and vegetation structure that facilitate dispersal
Barriers = regions a species is unable to colonize, inhibit dispersal
- ecological barriers: biotic interactions (hint think about biotic interactions). Examples
are cattle egret in the savannah.
- geographic barriers: physical barriers (see allopatric speciation, next lecture). Examples
A. Temporal Change: Population Growth Models
Simple Model of Population Growth
- consider a population
- how many ways can it change in size (individuals become more or less
- populations change in size due to interactions of individual organisms with the environment
Geometric Growth versus Logistic Growth
Geometric Growth e.g. Duckweed (Lemna minor)
-smallest flowering plant
-reproduces from seed or vegetatively (asexually)
Example of Population Crash e.g Kaibab deer in Arizona Logistic Growth
- in nature, populations increase to a relatively constant abundance according to
the logistic population growth model
K = carrying capacity = number of individuals of a species that can be supported
relatively continuously in a given environment
- as environmental factors fluctuate with time, the actual number of individuals in
the population also varies around K.
EVOLUTION: A POPULATION PROCESS
GEOB102: BIOGEOGRAPHY 3
EVOLUTION: A POPULATION PROCESS
A. Charles Darwin 1859: The Theory of Evolution
What do scientists mean by "theory"?
- in common use among non-scientists the term theory suggests that an idea remains
unproven or even dubious: “it’s just a theory”
- in science, theory is a large and important body of knowledge and explanatory
concepts that seeks to increase our understanding of a major natural phenomenon
- theory: a body of knowledge that is unlikely to be disproved, but is likely to be
improved through testing hypotheses using the scientific method.
B. Darwin’s Theory Rests on 6 Fundamental Propositions:
1. Individuals that make up populations vary.
2. At least some of the variation is heritable. Genes are the units passed from parents to
3. "The Struggle for Existence." All populations/species have biological potential to
populate much larger areas/ranges, but they do not as resources are limited and other
environmental conditions affect populations (not getting eaten before reproduce). 4. Different individuals possessing different traits leave different numbers of
5. "Survival of the Fittest" The number of descendants that an individual leaves depends
largely on interactions of the individual (and its characteristics/traits) with the
6. "Natural Selection." Individuals possessing genetically based traits that enhance their
survival and reproduction in a particular environment will leave more offspring. The
environment “selects” favourable traits. The population will change in genetic structure
with environmental change.
Evolution: change in gene frequency in a population over time. Changes lead to
differential survival and reproductive success of individuals and population evolve.
Adaptation by Natural Selection: genetically determined traits help individuals cope
with their environment. Arises through evolution of reproduction.
“Survival of the Fittest”: successful reproduction by individuals best adapted to the
environment ( those with best traits).
Example of evolutionary processes: Peppered Moth
CHANGE IN GENE FREQUENCY
Lichen killed = dark trees
Light moths = visible
Dark moths = camouflage
Light moths dispersed or were predated by birds
Dark moths > light moths
In-class assignment: Identify and briefly explain each of the six fundamental
propositions of the theory of evolution for the peppered moth.
1. Yes vary by color
2. Yes: control for color, genetic makeup switches.
3. Not being eaten by the birds.
4. Color determines survival from predators.
5. Those better camouflaged contribute to reproductive success of individuals.
6. Genes that control (black color).
C. Modern Genetics and Sources of Genetic Variation Mutation: change to genetic material (DNA) passed from parent to offspring
Recombination: offspring receives two slightly different copies of each gene from its
- number of possible genetic combinations is very large (can depend slightly on what
kind of gene it is)
- each individual is unique (change in morphology, physiology and behavior)
Polyploidy: offspring receive two sets of genes from each parent
- fertile, but cannot interbreed with original population = new species
(genes stick together and come as double copies)
Species: individuals capable of interbreeding to produce fertile offspring
Genotype: an organism’s full hereditary information – the particular set of genes it
Phenotype: actual, observed properties of an organism (morphology, development,
behaviour), results from interaction of genes + environment.
Speciation: set of processes by which species are differentiated and maintained:
1. Genetic variation
2. Natural selection: suitability of genes in the environment.
3. Genetic drift: random changes to the genetic composition of a breeding population
leading to changes in gene frequency. Overtime can lead to new species.
Gene flow: opposite to speciation (constant mixing of genes tends to dilute variation
and prevent differentiation.
-reduces processes of speciation
WAYS TO IMPROVE SPECIATION (DARIN'S FINCHES)...
Geographic isolation: facilitates speciation by isolating populations, preventing gene
flow, accentuates genetic drift
Adaptive radiation: new environment(s) provide opportunity for new species adjusted
to different habitat(s).
Allopatric speciation - evolution of a new species by geographic isolation (physical
-Barriers: plate tectonics, oceans or lakes, mountain ranges and deserts. Sympatric speciation Cichlid fish) - speciation within a population, no spatially isolation
-reproductive isolation: timing of reproduction, mate choice and ability to use habitat or
BIODIVERSITY AND GLOBAL ENVIRONMENTAL CHANGE
GEOB 102: BIOGEOGRAPHY 5
BIODIVERSITY AND GLOBAL ENVIRONMENTAL CHANGE
A. Definition- from the International Convention on Biodiversity
The variability among living organisms from all sources and the ecological complexes of which
they are a part. This includes diversity within species, between species, within communities,
ecosystems and landscapes. (include diversity within species, between species and within
- How many species exist today?
-1.75 million species known to western science
- estimates of 4-30 million species
-1million animals; 42,300 vertebrates, the remaining are invertebrates (75 % insects)
-250,000 plants, most are flowering plants (90% flowering plants)
- New species identified yearly
- terrestrial invertebrates (e.g. insects), soil and subterranean organisms
- freshwater and marine fish and other organisms (some still being discovered) B. Measuring Biodiversity
1. Species Composition
- identify and name the species in a community (between habitat types and tropical regions)
2. Species Diversity - 2 major components
a. species richness: number of species per unit area (e.g a count)
b. species evenness: distribution of individuals among species = relative abundance (e.g a
measure of equability)
-Diversity indices: combine richness and evenness.
e.g. Analysis of two gardens:
Richness in both A and B is 5
Which garden is richer? Both are 5
Which garden is more even? B
Which garden is more diverse? Community B
C. Loss of Biodiversity
Global Extinction = the fate of all species
- loss of all individuals of a given species, genus, family or order over its entire range
- unique genome is lost forever
- ancestor becomes extinct as a new species evolves
Local Extinction or Extirpation
- species is lost from one or more geographic areas but persists elsewhere Rates of Extinction
- over geologic time, more species have evolved and gone extinct than exist today
-background rate = continuous extinction through geologic time
- mass extinctions = periods of tremendous loss of biodiversity
- 6 mass extinctions in the geologic record
- 7th mass extinction = ongoing human impacts on global biodiversity
Primary causes of extinction today:
a. over-consumption by humans (over-harvesting, over hunting)
b. introduction of exotic invasive species
c. secondary losses when biotic interactions are jeopardized
d. loss of habitat
e.g. cumulative effects of re