chapter 8
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Chapter 8. Population Ecology. Types of Species in Communities. N ative species species that normally live in a particular community Nonnative species also referred to as “invasive” or “alien” species species that enter a new community either through immigration or introduction - PowerPoint PPT PresentationTRANSCRIPT
Population Ecology
Native speciesspecies that normally live in a particular
communityNonnative species
also referred to as “invasive” or “alien” speciesspecies that enter a new community either
through immigration or introductionIntroduction may be deliberate or accidentali.e. “killer bees,” Kudzu, zebra mussels, Asian
oysters, domesticated animals
species whose decline or migration indicates a significant change (damage) to a particular community
Serve as “early warning sentinels” of environmental degradation
Examples:AmphibiansTroutBirdsAquatic macroinvertebrates
species whose removal from its community may dramatically alter the structure and function of the community
roles:pollinatorstop predatorsdecomposers
species that alters its habitat in ways that benefit other species behaviors of such species
may influence succession and increase species richness
sometimes identical to the keystone species, while other times serves as a counterbalance
Examples: elephants, kelp, eastern hemlock, mussels
Three general patterns: (see below)Most populations live in clumps although other
patterns occur based on resource distribution.
Figure 8-2Figure 8-2
1. Resource availability varies from place to place.2. Living in herds, flocks, or schools provides
protection from predators and population declines.
Fish, birds, caribou, antelope, zebra
3. Predators that live in groups are afforded a better chance of catching prey and getting a meal.
Wolves, hunting dogs
4. Temporary animal groupings may occur for mating and caring for young.
Dolphin, albatross
Populations increase through births and immigration
Populations decrease through deaths and emigration
How fast a population grows or declines depends on its age structure.Prereproductive age: not mature enough to
reproduce.Reproductive age: those capable of reproduction.Postreproductive age: those too old to reproduce.
Populations with mostly reproductive individuals tend to increase.
Populations with mostly post-reproductive individuals tend to decrease.
Stable populations are equitability distributed among all three categories.
No population can increase its size indefinitely. There are always limits to population growth in nature.
Population change is a balance between:Biotic potential - the intrinsic rate of increase (rr) or the
rate at which a population would grow if it had unlimited resources and…
Environmental resistance – all the factors that act to limit the growth of a population.
Together these determine a populations carrying capacity (KK): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.
Exponential or geometric growth – starts slowly but accelerates rapidly as population increasesJ-shaped curve plotted on a graph of population
vs. timeLogistic growth – exponential growth followed
by a steady population decrease until the population size levels offS-shaped curveUsually levels off at or near the carrying capacityCarrying capacity is not fixed
Fig. 8-3, p. 163
EnvironmentalResistance
Time (t)
Po
pu
lat i
on
si z
e (N)
Carrying capacity (K)
ExponentialGrowth
BioticPotential
Exhibit four phasesLag – phase characterized by low birth rates, when
the population is adjusting to a new
environment
Growth – phase which shows a dramatic increase in population size (B+I > D+E)
Stationary – phase when then population is in dynamic
equilibrium (B+I = D+E)
Death – phase in which the population declines (B+I < D+E)
Members of populations which exceed their resources will die unless they adapt or move to an area with more resources.
Some populations overshootovershoot their carrying capacity.Reproductive time lagCauses a dieback or a crash
Some populations may increase their carrying capacity by developing adaptive traits (i.e. natural selection)
Some species maintain their carrying capacity by migrating to other areas.
Fig. 8-4, p. 164
Carrying capacity
Year
Nu
mb
er o
f sh
eep
(m
illi
on
s)Overshoot
Fig. 8-6, p. 165
Nu
mb
er o
f re
ind
eer
Populationovershootscarryingcapacity
Carryingcapacity
Year
PopulationCrashes
Population density: the number of individuals in a population found in a particular area or volume.A population’s density can affect how rapidly it
can grow or decline.Density dependent factors Density dependent factors include biotic factors like
disease, competition for resources, predation, and parasitism
Some population control factors are not affected by population density.Density independent factors Density independent factors include abiotic factors like
weather, fire, pollution, and habitat destruction
Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically.Stable: fluctuates slightly above and below
carrying capacity.Irruptive: populations explode and then crash to a
more stable level.short-lived, rapidly reproducing species (i.e. algae,
insects)Cyclic: populations fluctuate according to regular
cyclic or boom- and-bust cycles.close predator-prey interactions
Irregular: erratic changes possibly due to chaos or drastic change. populations that inhabit unstable or highly variable
environments
Fig. 8-7, p. 166
Po
pu
lati
on
siz
e (t
ho
usa
nd
s)
Year
LynxHare
Some species reproduce without having sex (asexual).Offspring are exact genetic copies (clones).
Others reproduce by having sex (sexual).Genetic material is mixture of two individuals.Disadvantages: males do not give birth, increase
chance of genetic errors and defects, courtship and mating rituals can be costly (energetically).
Major advantages: promotes genetic diversity, division of labor among the sexes may provide offspring greater protection through critical periods.
r-selected species: Large number of smaller offspring with little parental care
K-selected species: Fewer, larger offspring with higher invested parental care
Figure 8-9Figure 8-9
r-selected species tend to be opportunists while K-selected species tend to be competitors.
Figure 8-10Figure 8-10
The way to represent the age structure of a population is with a survivorship curve.
Late loss population live to an old age.Constant loss population die at all ages.Most members of early loss populations, die at
young ages.
age
Population Ecology. (1998) Cyber Ed.