Introduction to Wildlife & Fisheries ConservationWFSC 304

Lecture 16: Applied Population BiologyWhat do we need to know about a population in order to manage it?

Demographic parameters (birth rate, etc.) Habitat requirements (limiting factors that determine carrying capacity) Population dynamics (trends over time)

Demographic parameters1. Birth rate (natality)—Population measure of number of individuals produced

per unit of time. Mean litter size commonly used to compare populations2. Fecundity—number of offspring produced per female per bout

i. Accounted by ageii. E.g. clutch sizeiii. Depends on

1. The length of the breeding season2. Gestation period3. Nature of the reproductive cycle

a. Reproductive success often lowest in youngest and oldest females in population

b. Generally increases with age then decreasesc. The age that females begin breeding affects population

structured. Example: Black rhino females breed from age 4 to 10;

therefore, many nonbreeders in the populatione. Example: some ungulates breed at age 1 and breed

until they dief. Populations may differ in patterns

i. E.g. guppiesii. Predator sites have advanced maturity, increased

reproductive effort, many small offspring4. Maternal size or provisioning5. Fate of preceding neonates

3. Sex ratio4. Death rate (mortality)5. Survival by age—can be used to construct “life tables”

6. Age structure—to model pop dynamics realisticallya. The relative proportions of various age groups in a population.b. Affects birth rates when a population exhibits differences in age-specific

fecundity7. Dispersal (immigration and emigration)8. Number (abundance)9. Density—number per unit area

These factors collectively determine r, the rate of population increase• Measures a population’s general health by describing the average reaction of

all members in the population to the array of environmental influences• Intrinsic rate of increase (biotic potential) – the exponential rate at

which a population with a stable age distribution grows when no resource is limited.

• Can be used to compare with the observed rates of increase in nature• r limited by carrying capacity of the environment, K

DispersalMovement away from natural areas or into unfamiliar areas

Measured in rate and distance Mixing gene pools—once thought to prevent old-school long timeframe

speciation; now known to promote rapid ecological speciation by creating sexual selection (reinforcement).

Emigration – leave a population and do not returno Density-independent – innate o Density-dependent – population pressures

Immigration – one-way movement into another are or population

Modes of population regulationDENSITY INDEPENDENCE

Population growth rate does not depend on density E.g. catastrophic events or wide scale mortality

DENSITY DEPENDENCE Increased mortality or decreased natality due to shortage of resources Increased mortality due to increased predation or parasitism Increased mortality or decreased natality due to increased intensity of

intraspecific social interactions

The Allee effect is realized at low density, such as when individuals of a species are too sparse to find mates.What factor would you expect drives negative density-dependence in conchs?What is another possibility?

Estimating density in nature• Can measure presence/absence but is not as informative as density• Census (complete count) is ideal but extremely rare• Generally we sample the landscape and deduce a population estimation• Scale varies dramatically

• 2,000 barnacles/square meter• 0.025 field mice/square meter• 0.000004 deer/square meter

• Simpler for sessile organisms; organisms that move and intermix are troublesome

• What technique?

eDNA• Technique uses species-specific

sequence primers and PCR to check for DNA amplification—if you can make DNA from Atlantic pipefish primers, then Atlantic pipefish are in the water sampled

• Environmental DNA becoming more used• Most useful for presence/absence• Methods being developed for quantitative assessment

Mark-recapture• Population size is constant during study• Marking must not affect catchability• Marking cannot be lost• All individuals must be equally catchable• Captured animals must be a random sample of the population• Major methods:

• Lincoln-Peterson methodN = Number of animals in the population

n = Number of animals marked on the first visit

M = Number of animals captured on the second visit

m = Number of recaptured animals that were marked

N = Mn/mThis is a one capture/mark, one subsequent recapture approachOriginal capture and recapture effort should be equal

• Multiple capture/recapture methods (e.g. Schnabel, Schumacher-Eschmeyer, Jolly) developed for ongoing survey work

Quadrats and Line Transects• Randomly placed quadrats (e.g. m² PVC frames for forb sampling

• Line transects random or ordered by plan where species are noted in range of line (e.g. 1 m either side)

• Like you did in RENR 215 (Ecology Lab)

MigrationRecall that natural populations are habitat mosaics, like islands in a sea, connected by migration. We call the population structure layed out on habitat mosaics “metapopulations”

Mountain sheep metapopulation in southeastern California. The species has permanently occupied the mountain ranges shown in red, with populations of the sizes indicated. Mountain ranges in yellow do not currently have permanent mountain sheep populations though they may have been occupied in the past. The species has been reintroduced into the mountain ranges in purple and green is where natural recolonization occurred in the past 15 years. Arrows indicate observed sheep migrations. Human settlements, major highways and canals all of which are barriers to the animal’s movement are shown in black.

Individuals ecological interactions translate into population-level effects Landscape-level changes impact individuals and these effects carry through

also to the population level

It is eEasy to conduct spatially-explicit simulations if basic parameters can be estimated from real populations.

At left is an example of a simulation that helped inform refuge design for a threatened species in old-growth Pacific northwestern forests.