Download Lecture 3: Wildlife Ecological Principles and Population Ecology Part 2

Wildlife Populations
 Wildlife Population = Animals of the same species that
occupy and interbreed within a given area over a given time
period
 Population size (e.g. 10000 elk in Kentucky)
 4 factors that strongly influence population size are:
Immigration
Birth
Death
Emigration
Population Characteristics
 Density = (# individual animals/unit area)
 Birth Rate (Natality) = # births/per number of




individuals/year (per hundred, thousand, etc.)
Death Rate (Mortality) = # deaths/per number of
individuals/year
Population Growth = change in numbers over time
Age Structure = how many individuals in each age group
Sex Ratio – ratio of males:females
Demographic Terminology
Demography – the statistical study of populations.
AGE CLASSES (Spans pre-reproductive to reproductive to post-reproductive stages)
 Birth to a few months or 1 year old = “young” (cubs, pups, calves, fawns, kittens, nestlings,
etc.)
 Few months-2 years = (yearlings or juveniles; may or may not be reproductive)
 > few months, or 1-2 years-xx years = adults (most able to breed)
 > x-xx years = reproductively senescent (unable to breed) adults
For example: 0-1 year black bears are cubs, 1-2 year old bears are yearlings (note that males can
breed at this age), 3-4 year old female bears typically are young non-reproducing adults (males
still breeding), 4-13 years are reproductive male and female adults, and 13+ years are senescent
adult females (males likely still breeding).
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Remember, the actual ages that determine these classes can vary depending on species; the above longer-spanned time
categories largely holds true for mid-large sized mammals. Reproductive capability per age class also varies by sex since
males typically breed earlier and longer given that females have a limited number of eggs and decreasing capacity to
conceive and carry a fetus to term past their “prime age”. Sperm count and quality of males tends to decrease with age in a
similar way.
Population Density
(# animals/unit area)
10 km2 total area
with 8 goldenwinged warblers.
What is the
population density
per km2?
Dispersal = outward movements of individuals away from their
established areas of activity. Dispersal out (emigration) and
dispersal in (immigration) influences population size and
growth. (e.g. bears in Kentucky have dispersed from range in VA
and WV)
Natality (Birth Rate)
Natality = number of offspring per unit time, usually
one year. Has the greatest influence on population
growth. Varies with species, with populations, within
age classs, and with years. Highly dependent on
available resources and thus the condition of the
mother.
Death (Mortality) Rate
 Mortality Rate = # individuals dying/unit time, usually one
year. Life tables (both cohort and static) are commonly
used to examine the life history of populations and
understand survival/survivorship (your likelihood to
live/survive to a given time period). Total mortality of
wildlife usually = natural + harvested (hunted/trapped)
Cohort Life Table = Start with set
number and follow through lifetime.
Must start with lot of individuals and
monitor for very long time.
Static Life Table = Assess survival of a
handful of individuals from each age
class. Much easier to gather data in the
field.
Cohort Life Table (Isle Royale Moose)
This image cannot currently be displayed.
lx = number of animals remaining in population
dx = number that died in that year
qx = proportion of population that died in that year
ex = average life expectancy of remaining individuals (in years)
Survivorship Curves
 Survivorship curves often used to portray life tables
and are easier to visualize.
 Knowing animal life history strategies gives us clues as
to what common survivorship looks like over the
course of an animal’s lifetime.
 Type 1 Curve (k strategist)
 Type 2 Curve (in-between k and r strategies)
 Type 3 Curve (r strategists)
r – selected species (Reproduce
and forget about em’ strategy)
 Biotic potential
 High
 Juvenile mortality
 High
 Population turnover
 Rapid
 Age at first breeding
 Younger
 Body size
 Small
 Life span
 Short
 Dispersal rate
 Rapid
 Population stablity
 Low
 Successional stage
 Early to mid
K – selected (strong parental
investment in few offspring strategy)
 Biotic potential
 Low
 Juvenile mortality
 Low
 Population turnover
 Slow
 Age at first breeding
 Older
 Body size
 Large
 Life span
 Long
 Dispersal rate
 Slow
 Population stablity
 High
 Successional stage
 Mid to late
Pests
Cockroach
Norway rat
House mouse
Rock dove
(pigeon)
r - selected
Game
Species
Cottontail rabbit White-tailed deer
Elk
Mallard
Bobwhite Quail Moose
Black bear
Endangered
Species
Golden eagle
Whooping crane
African elephant
California condor
Some sharks
k - selected
1.0
Frequency
of Surviving 0.5
Type III
(r)
Type II
0.1
Age
increasing
Type I
(k)
Survivorship Curves
These curves can tell us not only information about relative lifespan and survival for
a given age of animal, but also about how harvest (hunting/trapping/fishing) may
impact population structure differently than natural predation (Fig 2-9)
How Animal Harvest Influences Mortality
Hunting, fishing, and
trapping are a type of
predation (when one
species consumes another).
When these activities
substitute for other forms
of natural mortality and do
not increase total mortality
it is considered a form of
compensatory mortality.
When these activities add to
total mortality it is called
additive mortality.
Sex Ratio
 Sex ratio= Ratio of males:females or vice-versa.
 Example: 61:39 (61 bull elk:39 cow elk in above photos)
 This value can inform us on potential breeding
capability of population, how management may have
impacted each sex, etc.
Age Structure
 Stable populations = birth rate ~ = date rate
 Increasing (growing) populations = birth rate > death rate; lots more youth in
population
 Decreasing (declining) population = death rate > birth rate; see lots more older
members in population relative to young.
Population Growth
The ability for a species to reproduce and grow in population
size is known as its biotic potential. Basically, how many offspring
could they potentially have under ~99% of usual circumstances.
Examples Biotic Potential
Deer = 2
Quail = 15
Bats = 1
Coyote = 8
The actual number added to the population on an annual basis
that become reproductive members of the population is
called recruitment. Using the same example, here’s what
typical recruitment #s are:
Deer = 1.3
Quail = 8.6
Bats = 0.9
Coyote = 2.5
Population Growth
Limited by the carrying capacity (k); the maximum
population size that environment /habitat can
support.
Population Growth
There are two general types of growth curves: J (unrestricted or
exponential growth) and S (restricted or logistic growth). J curves
are characteristic of r-selected species, while S curves typify kselected species. Why? R-selected species reproductive capacity
can temporarily outpace limiting growth factors, K-selected
reproduction is more limited and cannot (see next slide).
R-selected species can irruptively grow past their carrying capacity and are
more prone to boom-bust population cycles than k-selected which tend to be
more stable in their growth, but can be irruptive when placed into new areas,
when they recolonize areas, or in the absence of predation or competition.
Mice Population Explosion!
http://www.bing.com/videos/search?q=rat+population+explosion+austalia+you
tube&FORM=VIRE3#view=detail&mid=5120DC41F7F5655E13995120DC41F7F565
5E1399
Density-Independent Growth
Meaning that a population can grow irrespective of its density
Usually occurs early in exponential growth phases, particularly with rspecies
Density-Independent Limitations to Growth
Meaning that a population can be restricted in its growth by
factors independent of the population size. These are usually
abiotic (nutrients, climate, catastrophes, etc.)
But for all species, eventually the party is over with regards to
population growth; it will be slowed or halted by one or more
limiting factors (LFs) such as food, disease shelter, etc.
These LFs typically dictate carrying capacity (k).
Percent Population Loss
Density Independent Growth
Population Size Increasing
Density Dependent Growth
 Particularly at low population
densities, animals need to be able to
find mates, thus population growth
can depend on having a certain
density of individuals to make this
happen ; when they can’t this is
called the Allee effect (imagine a
lone man and woman released on
opposite ends of a planet we are
colonizing…not so good for
propagating our species there! Ditto
when we’re trying to reestablish
animal species)
Density Dependent
Limitations to Growth
 As numbers grow and population
density increases, then food, shelter,
water, and other resources become
limiting as intraspecific competition
increases. Also, disease and parasites
have an easier time moving between
these more crowded hosts, thus
mortality increases.
Percent Population Loss
Density Dependent Growth
Population Size Increasing
Inversity
When times are good (resources abundant), k-species in particular tend to
have higher number of offspring. When times are harsh (resources scarce),
tend to compensate and have fewer to no offspring. Example: Pronghorns
have more twins when resources are in good supply, and vice-versa.
Wildlife Management
Production & Yield
As mentioned before, much of wildlife management is focused on
manipulating populations of species; this is very much like raising
and harvesting an agricultural crop in terms of the way “numbers
of animals” are viewed and discussed.
Production – increasing the # of a species
Population Turnover - not a McDonald’s dessert menu item;
change in population size from year to year.
Yield – what we as humans reap from a species
Maximum Sustained Yield – maximum harvest of species without
driving down population size over a given time. This is the goal for
most game species. But, managers should be concerned with the
ecological carrying capacity (k) of the land so it is not damaged,
and the sociological carrying capacity of the people that have to
coexist with these animals. Concern for the entire ecological and
human communities is important.
During the course of a year, surplus created from newly born
individuals and immigrants are offset by loss from emigration and
death. Thus, a wildlife manager must be aware of and be able to
quantify how all these BIDE factors influence population size so they
can set harvest decisions that maintain the ecosystem and meet the
needs of stakeholders such as hunters, farmers, and wildlife
watchers(a very difficult job!).
Some common animal population growth
and size limitations
First and foremost, in Kentucky, food is rarely a limiting
factor; however, habitat availability and quality typically are
Examples of Limiting Factors in KY:
 Quail in Kentucky – nesting & brood (chicks) rearing habitat
 Tree Squirrels – hard mast production & nesting trees
 Wood Ducks – nesting trees and quality streams
Examples of Limiting Factors Elsewhere:
 African Wild Dogs – high lion and hyena density (interspecific
competition)
 Koalas – eucalyptus trees
Symbiotic Community Relationships
Important for Population Regulation
 Symbiosis – two or more species living together or in same
habitat.
 Parasitism – one species lives in or on another host (e.g. dogs and
tapeworms) and typically does not kill host.
http://www.youtube.com/watch?v=CzdhZQiRmic

Disease - when one species invades another causes a decrease in fitness or
death. Can be parasites, but most often are bacteria, viruses, fungi, prions,
and protozoans.
 Mutualism – when two species interact and benefit each other (e.g.
coyote and badger)
http://www.youtube.com/watch?v=hkTCkb9swvQ
 Commensalism – when two species interact, but only one benefits.
(e.g. cattle egrets following elephants and other large mammals that
kick up dirt and insects for the egrets to eat)
http://www.youtube.com/watch?v=vWk1Jhoh4ZA