04. DYNAMIC POPULATIONS Flashcards
Define population
- grp of indiv
- same spp
- same location
- rely on same resources
- influ by similar environ cond
- interact w e/o
What four factors influence population size?
births, deaths, emigration, immigration
What are the three types of population distribution
clumped, uniform, random
*occurs @ subpop lvl too
What causes a uniform distribution of individuals within a population?
comp for resources - either defensive/protective measure or simply X enough indiv in pop to live in close prox to e/o
Define population ecology
study of r/ship bw pops + environ + its resources. considers biotic + abiotic influences on pop abundance/distrib/comp
How can population ecology be applied?
measure:
- abundance
- birth/death rates
- mvmt
How might we reduce the size of a population?
Use rabbits as an example.
e.g. rabbits
- inc deaths - intro disease
- dec births - contraceptive in bait
- dec immig - fences
- inc emig - intro predator
Which members of a deer population would be most effective to target to control population size?
females
What two factors influence precision when estimating abundance via plot sampling?
- no. of plots
- variation in counts bw plots
Outline how sampling works
- select plots across portion of pop range
- count indiv in plot
- est avg density and detectability
- extrapolate to est whole pop
Equation for estimating abundance
N=n/p
N → abundance
n → # seen
p → prob of detection
Outline how mark-recapture works
- capture indiv + mark all of them - incl double colours to ID indiv
- return to pop + allow time to remix
- recapture + record how many were from 1st trap
- est prob of detection
Outline the key assumptions of mark-recapture
- marks remain
- marking is benign
- ethical - X harm indiv
- sci integrity - prob of recapture X impacted by org learning avoidant behaviour from 1st trap
failure → bias = systemic over/underest
- closed pop - X birth/death/mig
List some marking methods
- leg bands
- ear tags
- collars
- paints/dyes
List methods for counting/sampling
- mark-recapture
- natural marks (e.g. fur or fin patterns)
- genetic methods (collect genetic info to ID indivs)
- signs as indices (e.g. footprint, droppings)
Pros/cons of the use natural marks to estimate abundance
pros - non-interference w animals (ethical + X impact quality of data bc X learn avoidant behaviour)
cons - poss that patterns change during study period
Name the three broad phases of the life cycle
juvenile, reproduvtive, post-reproductive
How is the life cycle defined?
according to length of gen (several, annual, perennial) AND # reprod events/yr (interoparous vs semelparous)
Examples of semelparous vs iteroparous annuals
semelparous annuals - wheat, gypsy moth
iteroparous annuals - common groundsel, field grasshopper
What do perennial life cycle patterns indicate about food availability?
seasonal breeding → reprod in times of high food availability
consistent breeding → spp in areas w high food availability e.g. primates in tropics
Example of semelparous animal
pacific salmon - breeds once then dies
Define demography
study of birth/death rates of pops + how they change over time
What does a life table do?
tracks the fate of a set cohort from birth to death + records how many indiv survive each yr + how many offspring they prod
Outline the three types of survivorship curves
time vs log10(#surviving indiv)
Type I = log curve → most indiv die late e.g. elephants
Type II = linear slope → indiv die at uniform rate e.g. squirrels
Type III = neg exponential curve → most indiv die @ young age e.g. butterflies
What characterises population growth, decline and stability?
stable → R=1
growth → R>1
decl → R<1
Outline the difference between density-dependent and independent limits to population growth
ind - affects pop growth regardless of pop density (often abiotic) e.g. wildfires
dep - affects pop growth diff acc to pop density + often BC of pop density (often biotic) e.g. resource depletion
What is the ‘carrying capacity’ of a population?
max pop size that an environ can sustain i.e. births=death → stable pop
Outline negative density-dependent population regulation
- inc pop → dec growth rate
- occurs when carrying capacity = surpassed
Why does negative density-dependent population regulation occur?
- comp for resources
- inc opp for disease spread
- predation (preds pick more abundant prey spp)
- inc prod of toxic waste
What is a potential shortfall of the exponential growth projection?
ignores movement - only considers survivors/recuits
Under exponential growth…
the rate of inc (r) = constant
What does logistic growth project?
for density-dep growth, growth rate decl w inc abundance
Logistic growth equation
Image 4
Key assumptions of logistic growth model
- X variability of environ cond
- X effect of chance - esp influ in sml pops
- linear change in per cap growth rate w density
- X consider pop structure e.g. reprod stage → impact fecundity
- pop growth rate adjusts instantaneously → approach K smoothly i.e. X delays - esp problematic bc if delays do occur, pop will overshoot + overexploit resources → dec K
Compare stochastic and deterministic processes
diff = certainty of outcome - stoch process → outcome = uncertain vs determ process → outcome = certain
stoch = randomness
How does environmental stochasticity influence population dynamics?
variable resources/predators/shelter → variable birth/death rates
How does environmental stochasticity relates to density?
Environ stoch encompasses both density-dep and ind factors - either/both influ pop dynamics of diff spp at diff times
What does the term ‘demographic stochasticity’ mean?
random fluctuations in demographics of a pop
arises from chance birth/death of indiv
Which populations are most impacted by demographic stochasticity?
sml pop - chance of extinction = higher
How does demographic stochasticity affect the risk of extinction of a population?
always a chance of extinction, though v unlikely. Likelyhood dec as pop size inc
What does dispersal mean?
when indiv moves from one breeding location to another
What are the two types of dispersal?
natal disp - mvmt from birthplace to breeding place
breeding disp - change of breeding site
What two factors influence dispersal?
- age - mvmt prior to breeding
- sex - fem bias in birds vs male bias in mammals
Outline the modes of dispersal
animals
- active - fly, walk swim
- passive - currents, floods, attach to other animals/vehicles
plants
- gravity, wind, water, animals (attach/in gut), vehicles, machinery
How have humans introduced new modes of dispersal?
- attach to clothes
- purposefully intro invasive/non-native spp
- trades routes/vehicles = new vectors for mvmt e.g. starfish attach to bottom of cargo ship
How does dispersal commonly regulate population size
- migration out of pop → decl pop size
- intro of invasive pred spp → inc pred pop size/decl prey pop size
What are the three ways we can measure dispersal?
- marking & observation
- tracking tech
- instrinsic markers
What are the limitaions of measuring dispersal via marking and observation?
- observation effort
- gaps in data
- X track long dist mvmt
What are the three types of tracking technology used for measuring dispersal?
- radio tracking
- satellite tracking
- geotrackers
What are the pros/cons of measuring dispersal via radio tracking?
cons - researcher needs to be near animals to recieve signal
What are the pros/cons of measuring dispersal via satellite tracking?
pros - researcher X need to be nearby
cons - heavy
What are the pros/cons of measuring dispersal via geotrackers?
pros - lightweight
cons - limited accuracy bc relies on assumption that animal is in same spot @ sunrise/set - X acct for mvmt w/in day
How can we measure dispersal using intrinstic markers?
- measure stable isotopes - chemical composition reflects environ/diet
- genetic markers reveal where animal was born
- parasites = clues abt locations visited
Outline the factors influencing what dispersal measurement system is used
-size of animal
- habitat
- cost
- accuracy
- impact on animal + sci integrity
What are the five categories of metapopulation spatial dynamics?
- classic
- mainland-island (source-sink)
- patchy pop
- non-equilibrium (extinction w/out recol - often caused by habitat fragmentation by humans)
- mixtures
What characterises a ‘classic’ metapopulation?
frequent extinction and recolonisation in habitat patches
Populations that inhabit patchy habitats are not always metapopulations. Why?
metapop req some lvl of interaction bw pops
At the regional scale, what two factors drive metapopulation dynamics?
extinction + recol
Do metapopulations arise in natural or in transformed habitats?
transformed - habitat patches often arise from habitat fragmentation
What factors influence how prone a population is to extinction and recolonisation?
- larger terr → lower prob extinct
- larger aquatic veg cover → lower prob extinct
- inc connectictivity → lower prob extinct + inc prob recol
What is a life history strategy?
a spp’s pattern of growth, survival + reprod events
How have different life history strategies arisen?
LH strats = shaped by NS bc traits that max offspring survival = favoured over time - whether this is high fec/low PI or low fec/high PI depends on environ cond
What are the three categories of reproductive behaviour that reflect different life history strategies?
- fecundity vs parental care
- age at maturity (early vs late reprod)
- semelparity vs iteroparity (# of reprod events w/in lifetime)
Fecundity and parental investment have an _ relationship
inverse
What does a high fecundity/low parental investment life history strategy entail?
prod as many offspring as poss BUT each have low chance of survival bc too energetically expensive to protect(see Dihkstra 1990 - Eurasian kestrels caring for more offspring neg impact survival of parents)
h/e only 1 offspring has to survive for pop = stable
Pros/cons and characteristics of early reprod strategy
characteristics: short-lived + sml body size bc early E invested into reprod, X growth
pros: reduces risk of X reprod at all
cons: lim ability to prov parental care bc short life cycle → dec prob of survival
Examples of late reprod strategy
- elephant
- sharks - fishing esp problematic bc target larger animals = adults → X able to prov parental care to max capacity → impacts survival prob of young too (double whammy)
Define semelparous and give two examples
single reprod events before death e.g. pacific salmon, desert agave
Define iteroparous and give two examples
multi reprod events across lifetime e.g. humpback whales, mountain ash, humans
Most perennial plants are…
iteroparous
Example of an semelparous Australian mammal
monotremes
Characteristics of r-selected species
- density ind
- high fec rate
- short gestation
- low PI
- high mortality before indiv reach AoM
Characteristics of K-selected species
- density dep
- low fec
- higher PI
- low mort rate of indiv before reach AoM i.e. high survival prob
Example of how r-selected species rapidly adapt to changing environmental conditions
- desert locust pop boom when food = abundant + heavy RF
- this is bc fem mature early (1-6mo) + can lay 100s eggs + die after 3-6mo → makes 2-5 gens per yr
- altogether contrib to x10-16 inc in pop size each gen → swarm of 10K locusts can inc to 100bn in 7 gens = 2yrs
How do boom/bust cycles of r-selected species impact ecosystems?
pop fluctuation in r-selected spp has conseq across food chain → pop flux can be biotic, abiotic or both
Define parasite
org that obtains nutrients from another org, commonly harming host + poss causing death
Define infection
when parasite colonises host org
Define disease
when infection causese symptoms in host
Define pathogen
??
Define vector
org that carries + transmits infectious pathogen to another org
Define virulence
severity/harmfulness of disease
Outline the characteristics of micro- and macro-parasites
micro:
- sml + intra-cell
- multiply rapidly w/in host
- transmitted dir
- v numerous - viruses, bacteria, protozoa
- e.g. covid (virus) or Plasmodium falciparum (protozoa) → colonises human RBCs - mosquitos = vectors
macro:
- grow on/in body cavities
- reprod by releasing infectious stages into environ - poss col same host as parent
- rarely complete life cycle w/in one host
- e.g. helminths, nematode worms, lice, fleas, tapeworms
Outline the differen ways parasites are transmitted
- direct - X req vector e.g. smallpox
- trophic - eaten by host e.g. Leucochloridum = parasitic flatworm
- vector-transmitted - carried by other org e.g. dengue virus by mosq
Outline the different strategies employed by parasites
- parasitic castration - sterilise host + redir E/space typically used for reprod → grow/fuel parasite
- parasitoids - insects that kill host thru 1) stinging host + laying egg on dead body = food for young or 2) laying eggs dir inside host → emerge + kill host after hatching e.g. alien wasp
- micropredation - attack several hosts + usually feed on blood e.g. ticks, leeches, fleas
- brood parasites - use other spp to raise young e.g. Channel-billed cuckoos uses magpies/currawongs/crows
How common are parasites?
> 50% spp + >50% indiv = parasites (Windsor DA 1998)
Definition and characteristics of epidemics
- rapid changes in disease prevalence - often cause waves of infection
- can cause mass mortality
- disappear from host pop for period of time
- rapid inc pop growth rate after event bc more resource available per indiv
- e.g. 1995/98 pilchard herpesvirus in pilchard fish → 75% mortality
Definition and characteristics of endemic infections
- persist in specific pop for LT period w minimal prevalence flux
- can suppress pop #
- only dir caused spp extinct x1 - protozoan parasite caused Partula turgida snail extinct in 1996
- BUT can make pop more vulnerable to extinction bc suppress pop size (sml pops are more prone to extinct) e.g. TAS devil pop # decl 90% bc disease = v vulnerable
When is culling used to control disease spread?
when transmission = density dep i.e. when disease spreads best when too many animals
→ cull infected/vectors
What are three strategies for disease prevention and control of microparasites?
- culling (infected orgs/vectors)
- behav modif incl quarantine/soc dist
- vax e.g. measles
Why do parasites harm their host?
Provide a case study to support your claim.
virulence-transmission trade-off hypothesis argues optimal ongoing transmission occurs at an intermediate virulence lvl
i.e. beyond intermed virulence lvl cost of inc host mortality trumps benefit of inc transmission = X desirable for parasite survival/reprod
e.g. monarch butterflies + protazoan parasite (de Roode et al. 2008) shows optimal fitness (replication) = intermed vir
Outline two host responses to parasites
- host tolerance - ability to cope w infection of pathogen by minimising damage (but X reduce transmission)
- host resistance - ability to reduce prob of pathogenic infection/replication/transmission OR inc speed of pathogen clearance (recovery)
What is a threatened species?
pop/spp on path towards extinction
How many species are threatened with extinction?
> 32K = 27% all assessed spp (IUCN)
amphibians = most @ risk (41% spp) IUCN
What characteristics of a population make is more at risk of extinction?
- sml pop size (low genetic div + poss allee effects)
- sml geog range
- slow devt/reprod
- narrow eco niches
What is an allee effect?
when growth rate of sml pop = dec bc of undercrowding i.e. low pop density
Why do allee effects occur?
bc mate lim (most common), coop defense, pred saturation, coop breeding, coop feeding/dispersal
Why are allee effects relevant to conservation efforts?
sometimes even if remove threat that originally caused pop to decl, pop might still X be able to recover from Allee effects w/out help e.g. mt pygmy possum ‘love tunnel’ @ mt hotham
Outline how an allee affect via mate limitation can cause extinction
e.g. habitat fragmentation/destruction → trees too far apart from neighbours to pollinate
Outline how low genetic diversity can cause extinction
inbreeding depression
- inbreeding → inc homozyg → inc prob of indiv born w delet recessive alleles → threatens indiv survival/reprod → cascading conseq for pop survival in sml pops
- can cause extinct bc lower reprod fitness/opps (bc indiv death) → dec evol potential → less able to adapt to changing/new environ → poss extinct
Outline how small geographic range can cause extinction
sml range = inc risk that habitat destruction/fragmentation impacts spp entire range → disruptive events (a/biotic) impact survival of whole spp
Outline how a slow reproductive rate can cause extinction
inc risk that deaths>births bc X able to replace indiv as rapidly e.g. kakapo parrot only breeds every couple yrs + only lays 1-4 eggs/breeding cycle
Outline how narrow ecological niches can cause extinction
bc spp heavily relies on specific habitat + its resource → X able to adapt to new/changing environ → lack of fitness = fatal → decl pop numbers
e.g. mt pygmy possum rely on bogong moths = food
What are the key threats to threatened species globally? How do they differ from threats to Australian species and why?
global threats = habitat loss + overexploitation
Aus threats = invasive spp + changes in habitat bc historic genetic iso of Aus spp → high lvls endemism + specialisation → Aus spp X well adapted to cope w novel spp/environs
Outline habitat loss and degradation as a threat to threatened species globally
clearing for agri + urbanisation → habitat loss/degred/frag
→ creates habitat patches → pops can shrink bc:
- stochastic processes
- allee effects
- low genetic div
Outline overexploitation as a threat to threatened species globally
- animals/plants collected for food/medicines/pets
- lg/slow reprod spp = most vulnerable
- e.g. sharks = absent from 15% coral reefs bc overexpl
Outline invasive species as a threat to threatened species globally
- pest animals, plants + diseases
- impact pop size thru pred, comp for terr/resources or inc deaths bc toxic
- 10% Aus mammals = invasive spp → 22 spp native Aus mammals = extinct
Example of how threats are often overlapping
extinction of passenger pigeon from Nth Am
- pop = bns in early C19 → extinct in wild by 1901
- habiatat loss AND overexploitation
Name and outline three types of conservation interventions
- threat reduction
- habitat restoration, dec exploitation, dec invasive spp
- facilitated by est reserves
- e.g. croc hunting ban 1970s → saltwater croc pop recover from ~3000 to >100K now
- e.g. humpback whales - dec hunting → pop recover from 100s in 1960s
- population boosting
- captive breeding
- combo w threat reduction to ensure LT success
- e.g. Lord Howe stick insect - captive breeding program @ melb zoo + removal of rats from LHI → pop successfully recovered
- genetic rescue
- recieve genes from diff pop to inc genetic div → resolves inbreeding depression
- e.g. mt pygmy possum - intro males from nearby pop into struggling Buller pop → successful pop growth + inc genetic div (Weeks et al. 2017)
