Transcript Distribution - Gustavus Adolphus College

What limits/influences distributions?
1) Historical Factors
– factors associated with past events or distance (in
geologic time); contingency and priority effects
2) Contemporary Factors
– factors operating in ecological time (e.g. behavioral,
abiotic and biotic factors) that limit or affect patterns
of distribution
1) Historical Factors
Evidence that geologic history plays a role in distributions:
A. Continental drift – Marsupial, ratite and Nothofagus
distribution (vicariance explanation - fragmentation of environ;
ie. splitting of a tectonic plate) in contrast to dispersal limits
B. Glaciation – Temperate forest tree distributions
C. Area spatially inaccessible – non-native species (e.g.
starlings, cane toads, large mammals on islands, etc)
D. Insufficient time (relative to dispersal speed)
How can we determine if historical or
contemporary factors have affected
distributions?
Examine historical record
Fig. 3.1
Examine fossil record and consider continental drift
Godwana in Permian (286-245 mya). See also Fig. 4.7 in Krebs
Outside of range
Fig. 3.2
Do manipulative/transplant experiments
2) Contemporary factors
A. Habitat selection – Why are some habitats occupied?
Individuals ‘choose’ based on stimuli from:
1.
2.
3.
4.
5.
Landscape, terrain
Type of nesting or feeding sites
Density of resources &/or conspecifics
Life stage, size of individual
‘Cultural’ based on early experiences
Evol’n reasons – ultimate reason(s)
Ecological reasons – proximate
worst
best
Fig. 5.8. Ideal distribution model of habitat selection
2) Contemporary factors
A) Habitat selection – individuals ‘choose’ based on
stimuli from:
1.
2.
3.
4.
5.
Landscape, terrain
Type of nesting or feeding sites
Density of resources &/or conspecifics (aphids)
Life stage, size of individual
‘Cultural’ based on early experiences
Evol’n reasons – ultimate reason(s)
Ecological reasons – proximate
2) Contemporary factors
B. Biotic factors
1.
2.
3.
4.
Limitation by competition
Limitation by predation
Allelopathy
Mutualism
2) Contemporary factors
C. Abiotic factors – means and extremes
– Leibig’s rule of the minimum
– Shelford’s law of tolerance
– Acclimation
Fig. 3.3
How do organisms expand ranges?
Modes of dispersal
1. Diffusion - gradual spread
2. Jump- movement across long distance
“Colonization rates are driven not by the mean
dispersal rates, but by extreme dispersal events
(Krebs 2001).”
3. Secular - spread in conjunction with adaptation
Fig. 4.1 Zebra mussel dispersal; Sometimes all three operate together
Fig. 5.2. Multiple causation; factors that affect realized niche