Lecture 21 Flashcards
stochasticity
randomness
Deterministic vs stochastic processes
stochastic - outcome is uncertain e.g. rolling a dice
deterministic - outcome is certain e.g. exponential vs logistic models
What is one possible source of variation in animal populations?
environmental stochasticity - unpredictable fluctuation in env conditions
- variability in rainfall, temp, etc.
- variability in resources (e.g. food, predators, conditions)
- variability in birth + death rates
density-dependent and density-independent factors . . .
drive population dynamics of some species
Demographic stochasticity
- arises from the chance birth and death of individuals
- analogous to coin throwing
- demographic stochasticity becomes more important as population size declines
the AVERAGE is very close to a DETERMINISTIC projection
Migration
the seasonal movement of animals from one habitat to another in search of food, better conditions, or reproductive needs.
Disperal
the movement from one breeding location to another - often influenced by age + sex (female vs male bias)
natal dispersal - from place of birth to place of first breeding
breeding dispersal - change of place of breeding
Modes of dispersal
animals:
active - fly, walk, swim
passive - currents, floods, attach to other animals, vehicles
plants:
gravity, wind, water, animals, vehicles/machinery
Dispersal has a fundamental influence on population dynamics
- invasive species
- dynamics of metapopulations (contribute to local extinction, colonisation)
How to measure dispersal
- marking + observation
- tracking technology
- intrinsic markers
Cons of marking + observation
- observation effort
- gaps in data
- long-distance movement
Radio tracking
- VHF transmitter on animal sends signal
- researcher picks up signal on receiver
- CON — need to be near the animal
- alt. to this is satellite tracking (transmitter on animal sends radio signal, satellite picks up signal, sent to researcher)
Geologgers
- record light level over time
- retrieve data and infer location (sunrise / sunset times)
very light-weight so don’t affect movement as much
Intrinsic markers
chemical composition reflects environment + food
- stable isotopes
- trace elements
ratio b/w different isotopes makes it possible to work out where the organism was
also types of parasites in organism
- as w as genetic makeup (genetic mark-ups)
Trade-offs to consider when trying to measure dispersal
- impact on animal (handling & device)
- accuracy of information
- size of the device, its price, and its data collection capacity
