BIOLOGY 2F03 Lecture Notes - Lecture 10: Western Grey Kangaroo, Semibalanus Balanoides, Eastern Grey Kangaroo
26 Nov 2016
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Chapter 10: Distribution and Abundance of populations and Species
• Population: a group of potentially interbreeding individuals of a single species inhabiting a
certain area
• Many attributes of pop. are determined by interactions between physiological ecology of
species and the biotic/abiotic conditions that individuals encounter
• Ecologists study populations for a few reasons
o Detailed understanding of natural pop. can provide insight into general processes
that drive ecological interactions.
o Population level interactions serve as foundation for many resources-based
economies, are strong societal pressures to understand population dynamics
o Study of many species at risk, recovery plans to allow for recovery of threatened
populations.
o Another great pressure faced by plant/animal species is the exponential growth of
human population
• All pop. share several characteristics
o Distribution: includes size, shape, location of area (volume) the pop. occupies
o Number of individuals within it and its density (# of individuals per unit area)
o Population density can be refined to either absolute density or ecological density.
o Absolute density: what most scientists refer to when they simply say “density”. #
of individuals of a pop. per unit area
o Ecological Density: uses concept of niche, not all of the conditions found within
a given area will contain the niche requirements of a particular species
o focus on distribution, abundance, dispersal
10.1 Distribution Limits
• Physical environment limits the geographic distribution of species.
• Species should only be found in locations that falls under their specific niche requirement.
• A determining factor of the geographic distribution of a species will be the underlying
distribution of biotic and abiotic conditions in combination with a species’ niche
requirements
• When species occupy habitats that contain conditions on the edge of those found within the
niche, metabolic costs for compensating for environmental stressors will take up grater part
of organism’s energy budget. Physical environment places limit on distributions of pop.
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• The Macropodidea include kangaroo/wallabies
• Caughley found close relationship between climate and distributions of 3 largest kangaroos
o Eastern grey kangaroo (EGK) confined to eastern third of continent. Includes
temperate forest (SE), tropical forests (N), mountains (central). Climactic factor
that distinguishes varied biomes is little seasonal variation in precip. or
dominance by summer precip.
o Western grey kangaroo (WGK) lives in southern/western regions. Distribution
depends on temperate woodland and shrub land biome. Climactic feature is
predominance of winter rainfall.
o Red kangaroo (RK) distributed in arid and semiarid interior. Covers savanna and
desert biome. Occupies the hottest/driest areas
• These 3 kangaroo species cover most of Australia; none live in northernmost region where
tropical forests are common.
• Caughly explains that northernmost areas are to hot for EGK, too wet for RK and to hot in
the summer/too dry in winter for WGK
• These limited distributions are not determined by climate directly
• The kangaroo may lack adaptations for certain conditions, not enough good/habitat, too
many pathogens/competitors
• The tiger beetle (C. longilabris) lives at high altitudes and elevations than any other tiger
beetle species. Yukon to eastern Canada
o Lives in northern temperate/boreal forests. Can reach Arizona/New Mexico,
southern pop. confined to montane coniferous forests (similar climate to boreal)
o During last glacial period, it lived more south than it does now. Due to melting of
glaciers they moved northward. Beetles in south live in isolated mountaintop pop.
o Schultz studied enviro. Physiology of separated pop of these species. Compared
physiological characteristics of pop. from Maine, Wisconsin, Colorado and
Northern Arizona. Measured water loss rates, metabolic rates, and body temp.
preferences
o Metabolic rates are higher and preferred body temp. (35*C) lower than other tiger
beetle species, supports hypothesis that C. longilabris is adapted to cool climate of
boreal/montane forests.
o None of the measurements differed significantly among pop. physical enviro.
Limits distributions of species, these limits may be stable for a long time
• Organisms in intertidal zone have evolved different degrees of resistance to drying, major
factor to zonation among intertidal organisms
• Barnacles show pattern of zonation.
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• Connell described that Chthamalus stellatus restricted to upper levels, while Balanus
balanoides are limited to middle/lower levels.
• What role does resistance to drying play in the intertidal zonation of these two species?
o 1955 warm weather with calm seas/low tides caused no water to reach upper
intertidal zones occupied by both species. During this Balanus in upper zone had
higher mortality than Chthamalus. But Balanus in lower zones showed normal
rates of mortality.
o Balanus appears to be more vulnerable to drying/dehydration. Higher rates of
drying/dehydration exclude these barnacle species from upper intertidal zone
• What excludes Chthamalus from the lower intertidal zone?
o Larvae settle in lower zone, adults do not survive there
o Connell transplanted adult Chthamalus to lower zone and found transplanted
adults survive well in lower zone
• If the physical environment does not include Chthamalus from lower zone, what does?
o Chthamalus is excluded from lower zone by competitive interactions with
Balanus
• Biological factors sometimes are more important than physical factors when determining
distribution/abundance.
10.2 Dispersal
• Dispersal can alter species distributions and local population densities.
• Immigration: Dispersal into the local pop.
• Emigration: Dispersal out of the local pop.
• Dispersal of individuals allows for metapopulations, has important consequences for natural
communities.
• Dispersal is different from migration. Migration is the seasonal movement of individuals
from one location to another, dispersal is a permanent migration from one pop. into another
• Expanding pop. are in process of increasing geo. Range
• Why should this type of pop. provide us with some of the best records of species dispersal?
o New species in area is recorded quickly. Ex. Expansion of Africanized bees
through S and N America is well documented, aggressiveness of these bees makes
sure their dispersal is always noticed
• Honeybees (Apis melifera) evolved in Africa/Europe. Range extends from tropical to cold,
temperate enviro.
o Differentiated into several locally adapted subspecies.
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Document Summary
Physical environment places limit on distributions of pop: the macropodidea include kangaroo/wallabies, caughley found close relationship between climate and distributions of 3 largest kangaroos, eastern grey kangaroo (egk) confined to eastern third of continent. Includes temperate forest (se), tropical forests (n), mountains (central). Climactic factor that distinguishes varied biomes is little seasonal variation in precip. or dominance by summer precip: western grey kangaroo (wgk) lives in southern/western regions. Distribution depends on temperate woodland and shrub land biome. Climactic feature is predominance of winter rainfall: red kangaroo (rk) distributed in arid and semiarid interior. Yukon to eastern canada: lives in northern temperate/boreal forests. Can reach arizona/new mexico, southern pop. confined to montane coniferous forests (similar climate to boreal: during last glacial period, it lived more south than it does now. Due to melting of glaciers they moved northward. Beetles in south live in isolated mountaintop pop: schultz studied enviro. Compared physiological characteristics of pop. from maine, wisconsin, colorado and.
