Explanations for Plant and Animal Distributions
I. Ecological
A. Tolerance / Limits
Bioclimatic Frontiers
B. Species Interactions
C. Succession
Primary, Secondary
II. Historical
A. Evolution
B. Speciation
C. Extinction
D. Dispersal
I. Ecological Biogeography
A. Tolerance / Limit
Plant’s survival depends on tolerance of environment
Climate, soil, biota, topography, fire
evolved means of coping with various environments: adaptations
e.g.: drought
Examples of Types of Adaptations:
Xerophytic: adapted to drought
Examples:
1. Waxy coatings on leaves (seal in water vapor)
Tropophytic: adapted to wet-dry (heavy rain/ drought) climates
Example: Deciduous trees: drop leaves after wet season; dormant during dry
Hydrophytic: water-tolerant; require saturation
Halophytic: salt-tolerant
Animal adaptationsto temperature:
Cold-blooded: no internal temperature regulation
Active during warm; dormant during cold
Hibernation
Warm-blooded: metabolism maintains constant temperature
Fur, hair, feathers, fat
Sweating, panting
Bioclimatic frontiers
Boundary marking limits of species’ tolerance to environmental factors
B. Species Interactions
1) Competition: both species require a common resource; niche overlap
And NUH is the letter I use to spell Nutches,Who live in small caves, known as Niches, for hutches.These Nutches have troubles, the biggest of which isThe fact there are many more Nutches than Niches.Each Nutch in a Nich knows that some other NutchWould like to move into his Nich very much.So each Nutch in a Nich has to watch that small NichOr Nutches who haven't got Niches will snitch.
Dr. Seuss - On Beyond Zebra (1955)
2) Predation: one species preys on (eats) another
3) Parasitism: one species gains nutrition from the other
4) Symbiosis: some benefit gained
Commensalism: one benefits, other not affected
Mutualism: both benefit
C. Ecological Succession
Change in species composition, structure or architecture of vegetation through time.
Sequence of communities that blend into one another gradually over time.
Development of plant community is gradual !
various communities occupy a habitat until a final, stable CLIMAX community is established.
May take <100 – 1000’s years
Several different sequences can produce same climax community
Example: Isle Royale….
Primary vs. Secondary Succession:
Primary: occurs on sites with no (or very little)vestige of a former community
Mt. St. Helens
Cooled lava flow
Strip mines
Secondary: habitat not completely sterile; some members of previous community present
Forest fire (mild)
Abandoned agricultural field
Flooded land
Examples of succession:
1. Pond Bog Forest
2. New volcanic eruption
Krakatau example:
9 months: tiny spider was found
>12 months: grasses
< 50 years: dense rain forest
How did seeds get there?
Wind, carried on/in animals
Swimming, rafting
storms
3. Old field
About succession… Climax community depends on climate
Colonization of bare ground depends on availability of seeds
Same climax community can be reached through different series of steps
Succession modifies environment
II. Historical biogeography
A. Evolutionexplains the history and biodiversityof life on Earth
40,000 microorganisms
350,000 plants
2.2 million animals
800,000 insects (1/3)
Definition: descent with modification:
All life shares common ancestor.
By having generation after generation of descendants with modifications, the immense diversity of life arose.
Key is variation:Difference between parent and offspring
Darwin 1859 :
Variationacted upon by natural selection over time brings about new species.
Favorable traits become more common in successive generations of a population. Variations are inherited; those that survive are those with variations that enhance their survival.
Darwin lacked mechanism for variation
Mechanisms of evolution:mutation and recombination
Has to be a change in genetic frequency in a population over time.
Mutations
altered genetic material; create genetic variation
Most are benign or not beneficial; some increase survival rate (those are passed on)
Recombinations
Each offspring gets 2 different alleles (copies) of each gene; many 1000s of genes per organism yields enormous possible genetic combinations : variations
B. Speciation
Means by which species are differentiated and maintained:
Mutation
Natural selection
Genetic Drift: change in gene pool due to chance rather than natural selection
Geographic Isolation : populations diverge and lose ability to interbreed
C. Extinction
Conditions change more rapidly than a population’s ability to evolve new adaptations.
D. Dispersal
Species move from one location to another; colonize new areas
Example: hemlock exercise in lab