Rate of increase reveals much more about a population than the speed with which it grows. It measures a population’s general well-being, describing the average reaction of all members of the population to the collective action of all environmental influences. No other statistic summarizes so concisely the demographic vigour of a population.
G. Caughley
Population Ecology: The Basics
• How do births, deaths, immigration, & emigration affect wildlife populations?
• What affects births, deaths, immigration, & emigration?
• What are demographic characteristics?
• What is the difference between exponential & logistic population growth?
Population Ecology: The Basics
• What is Aldo’s model?
• What is carrying capacity?
• What are patterns of abundance and what controls them?
• What is metapopulation and how does it relate to wildlife population dynamics?
• Who cares?
Population Ecology: The Basics
• What is a population?
• Why not deal with individuals?
(U.S Fish & Wildlife Service) (U.S Fish & Wildlife Service)
Population Ecology: The Basics
• N = B + I – D – E (demographic characteristics)
• Nt+1 = Nt + Bt + It – Dt – Et
N
Effects of: Harvest Restocking Habitat Weather Other organisms
Population SizeBirths
Deaths
Immigration
Emigration
♂:♀
Juvenile:Adult
Population Ecology: The Basics
• Population growth without resource limitation– Exponential
• Nt = N0ert • dN/dt = N/t = rN
– Assumes no I & E or I = E– Assumes no structure
– r» Instantaneous rate of increase,
intrinsic rate of increase, Malthusian parameter, or per capita rate of increase
» b - d» Units: ind/(ind*time)» Based on 0
N
Time
A B
N
dN/d
t
A B
Biotic Potential
C
Population Ecology: The Basics• Population growth with resource limitation (in relation to conditions)
– Logistic growth• Nt = K/(1 + [{K - N0}/N0]e-rt)• dN/dt = rN(1 - [N/K])
– Assumes no I & E or I = E– Assumes no structure
– K = carrying capacity» Max. # the environment can support» Assumes constant K» Can change with time & space» K = N?» K > N?» K < N?» K = ∞?
– Density-dependence N
dN/d
tN
Time
Accelerating Phase
K
Inflection Point (½ K)
DeceleratingPhase
Inflection Point (½ K)
K
Population Ecology: The Basics
• Population growth with resource limitation (in relation to conditions)
– Logistic growth• Nt = K/(1 + [{K - N0}/N0]e-rt)• dN/dt = rN(1 - [N/K])
– r v. dN/dt
– Unused portion of carrying capacity» (1 - [N/K])
» N = 2, K = 100 → 0.98» N = 98, K = 100 → 0.02
N
dN/d
tN
Time
Accelerating Phase
K
Inflection Point (½ K)
DeceleratingPhase
Inflection Point (½ K)
K
Population Ecology: The Basics
• What is this thing called Carrying Capacity?
– Ecologically-based • K-carrying capacity (KCC)
– Socio-economically-based• I-carrying capacity (ICC)• Optimum carrying capacity (OCC)• Minimum-impact carrying capacity (MCC)
– Animals must be removed
N
Time
MCC
KCC
ICC (½ K) OCC
Population Ecology: The Basics• Aldo Leopold’s Population Model
– Decimating factors– Welfare factors
– Other possibilities?• Exposure• Space• Harvest = removal
– The limiting factor (link)?
– Influences• Land-uses• Weather• Fire
N
Time
K
Inflection Point (½ K)
Hunting (Harvest)
Diseases & Parasites
Accidents
Starvation
FoodCoverW
ater
Special Factors
WelfareFactors
Predation
Env
ironm
enta
l Res
ista
nce
DecimatingFactors
Biotic Potential
Population Ecology: The Basics
• Other patterns of abundance– Density-dependent v. density-independent factors– Causes?
N
Time
N
Time
N
Time
D
BA
N
Time
C
KK
K
Population Ecology: The Basics
• Metapopulations– Groups of local populations
• Subpopulations or demes• Size, quality, connectivity, & distance (I & E are important)
– Island Biogeography & Conservation Biology» Matrix
Population Ecology: The Basics
• Minimum viable populations (MVP)– National Forest Management Act of 1976
– Species- & site-specific
– 50/500 rule
USDA photo by: Bob Nichols
Population Ecology: The Basics• Minimum viable populations (MVP)
– Shaffer (1981)• Need for performance criteria
• 99% chance of surviving for 1000 years despite stochastic events
– Genetic stochasticity– Environmental stochasticity– Natural catastrophes– Demographic stochasticity
» BBDBBD v. DDBBBB
– Importance of individuals• Florida panther
(U.S Fish & Wildlife Service)
Population Ecology: The Basics
• Effects of sex & age structure on population growth?
Population SizeBirths
Deaths
Immigration
Emigration
♂:♀
Juvenile:Adult
Population Ecology: The Basics
• So what!
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