population dynamic Flashcards
Definition of population
A group of individuals of a single species living in the same general area, so that members
• rely on the same resources
• are influenced by similar environmental factors
• are likely to interact and breed with one another
Properties of populations
Boundaries
Size/Density (Not a static property)
Distribution (clumped, uniformed or random)
Structure (age structure, sex ratio)
Boundaries
- Before studying a population, we need to define its boundaries
- May be natural ones (e.g. island, lake)
- Or arbitrarily defined (e.g. a specific area of a national park)
- Need to be appropriate to the organism under study and to the questions asked
What is population ecology
- The scientific study of of populations in relation to their environment
- i.e. how biotic and abiotic factors influence the abundance, dispersion and composition of populations
Why is population ecology important
- Sometimes pure scientific interest, but often applied focus
- Understand, but also predict and manage
- Guide how to:
- Conserve threatened species
- Control pests
- Manage harvested species
Managing populations
• Can act on different processes (births, deaths, immigration, emigration)
Step in Quantifying aspects of populations
- This may include:
- Estimating the size of the population
- Monitoring fecundity and survival
- Monitoring movement
estimating population size
Counting
• In some rare cases, may count all individuals in the population…
Sampling
…. but in most cases we need to use sampling techniques to estimate the size of a population
Sampling method
Set plots randomly
• Count within plots
• Calculate average density
• Extend estimate to whole area
Precision depends on:
• Number of plots
• Variability in counts
Mark-recapture technique
First sampling session (e.g. �”=12 individuals captured)
Marked (in some appropriate way), then released
WAIT FOR INDIVIDUALS TO MIX BACK WITH REST OF POPULATION
Capture a second time
estimated population= firstcapture number x second capture number divided by number of recapture
Some key assumptions in mark-recapture
• Marks are not lost between sampling sessions
• Marking does not alter the behaviour of individuals (trap-shy; trap-happy)
• No births, deaths, immigration, emigration between sessions (= closed population)
à If assumptions not well met, estimates will be biased (population size underestimated/overestimated)
à Model extensions exist to deal with some of these issues, e.g. suite of methods for open populations
markings
-NATURAL MARKS
-ARTIFICIAL MARKS (tag, paint, band, PIT tags)
• Batch marking vs. individual marking
• Invasiveness of marks (ethics; assumptions method)
NON-INVASIVE GENETIC METHODS ( DNA analysis of animal product that was left behind)
A typical life style Life cycle
- after birth is a juvenile phase mostly for growth
- growth stoped and move into reproductive phase
- after reproductive phase enter post reproductive phase and death by senesceane
Life cycles of all (unitary) organisms are variations of this basic outline
Difference in life cycle
• Length of generations
- Several generations per year
- One generation per year (annual)
- One generation over several years (perennial)
• Repeated reproduction?
- Iteroparous species: individuals breed multiple times; resources during breeding dedicated to
future survival
- Semelparous species: single reproductive event; no resources dedicated to future survival;
reproduction followed quickly by death
- We can find iteroparous and semelparous species among both annual and perennial species
Longer life cycles breeding
- Seasonal breeding, triggered by photoperiod, to match to availability of abundant resources
- Continuous breeding (e.g. in equatorial areas with little variability in temperature, rain, photoperiod; many primates)
- Semelparous species; most life in pre-reproductive stage, then breed and die
Demography and life tables
• To assess how the patterns of birth and death affect how a population may grow or decline in specific scenarios,
we need to monitor them in a quantitative way
• Demography: the study of the vital statistics of populations and how they change over time
• A useful way to summarise demographic information for a population is to make a life table
• To build a life table:
• We usually follow the fate of a cohort (a group of individuals of same age) from birth to death
• We determine the proportion of the cohort that survives from one age group to the next…
• … and the number of offspring produced in each age group
Survivorship curves
- A graphical representation of the survival rate data in a life table
- Plot of the proportion of a cohort still alive at each age (column 3 in previous life table)
- Usually plot log() values
Survivorship curves type
- type 1 Most individuals die late in life
- type 2 Individuals die at a uniform rate
- type 3 Most individuals die at a young age
Population dynamics
• Size is not a static property of populations. Populations can grow or decline in size
Change include birth, death, immigrate, emigrate
Problem with growth
When resources are abundant, populations have the potential to grow greatly…… but populations cannot grow infinitely!
Exponential growth = growth proportional to the population size
Types of mechanisms that limit population growth
Density independant
-any force that affects the growth of a population regardless of the density of the population. often abiotic
Density dependant
-factors that affect the growth of a population differently depending on the density of the pop. à often biotic
Negative density-dependence population growth rate decreases because the population is too crowded
Positive density-dependence population growth rate decreases because the population is too small
Density-dependent population regulation
- Negative density-dependence introduces a negative feedback in the system
- Population ↑ à Growth rate ↓
- “Stable” system, maximum population size
Carrying capacity = the maximum population size of a species that an environment can sustain Carrying capacity can vary substantially in space and time!
Density-dependence mechanisms
- INTRASPECIFIC COMPETITION FOR RESOURCES (FOOD, SPACE)
- DISEASE
- PREDATION
- TOXIC WASTES
Controversy: importance of density-dependent regulation vs. density independent factors?
some argue that density-dependant regulator and mainly competition is the main reason for limit in pop
some suggest fluctuation in the enviroment
-both is right, case specific
Mathematical models
- equation, or set of equations, used to describe a phenomenon
- quantitative representation of the truth
- a simplified one, but hopefully a useful one!
- balance between complexity and utility
- include model parameters that take different values depending on the scenario that is being represented
Exponential growth model (discrete)
Let’s consider:
- Discrete time (e.g. t refers to year t)
- Births and deaths only (we’ll talk about movement in the next lecture)
- Females (more convenient for modelling, common practice)
pop size at time t+1 = pop size at time � + births − deaths
Nt+1=Nt+Ntbt-Ntdt =Nt(1+bt-dt) =Nt(1+rt)= Ntrt
Nt=N0(1+r)t
Logistic growth model
Logistic growth model (discrete)
Logistic growth model (continuous)
Model assumptions and departures of logistical growth model
- Like all models, the logistic model makes assumptions
- If not met it lead to fluctuations in the population growth trajectory compared to the real model
Some assumptions:
- No variability in the environment (constant intrinsic growth rate and carrying capacity)
- No effects of chance (particularly relevant for small pops!)
- No consideration of population structure
- No delays (i.e. populations adjust growth instantaneously approaching carrying capacity smoothly)
- If there are delays, a population may overshoot carrying capacity.
- And during an overshoot period, the carrying capacity may be lowered by resource destruction
What is stochasticity?
- Stochasticity = randomness
- A process is stochastic if it cannot be predicted accurately
- E.g. roll of a dice (we can predict the frequency of events, but not their order)
deterministic
no randomness involved
Environmental stochasticity
- Unpredictable fluctuation in environmental conditions in space and time
- E.g. variability in rainfall, temperature, etc… and through this also variability in resources, e.g. food
resources and conditions that individuals need to survive and reproduce are not constant -> birth and death rates (and therefore growth rate) are not constant
Demographic stochasticity
- Arises because the processes of birth and death of individuals are probabilistic
- Even if the birth and death rates are constant, from year to year, there will be variability in the actual proportion of individuals that are born or die
An example of demographic stochasticity
- Population of individuals, all equal, with a survival probability of 0.6
- If there are 10 individuals… 6 individuals will survive to the next time step? Could be… but maybe not!
- In proportion, more variability the smaller the population
- Increases the risk of extinction in small populations
Accounting for stochasticity
- Both environmental and demographic stochasticity can be important for the dynamics of populations
- Not considered in the deterministic exponential and logistic population growth models
- But there are more advanced modelling approaches that allow accounting for these sources of variability (and other aspects, e.g. population structure)
Definitions: dispersal
- Most often used to describe the spreading of individuals away from others
- Can be divided in 3 phases: emigration/transfer/immigration
Definitions: migration
Mass directional movement of a large number of individuals of a species from one location to another
Dispersal
- Organisms need resources and good conditions for reproduction and survival
- There may be forces favouring aggregation… (e.g. individuals gather around a resource or for protection)
- … and forces favouring separation (e.g. individuals moving away to avoid competition)
à Dispersal is often age and sex biased (young, males)
- Immigrants/emigrants not only influence population size, but can also affect its composition _> Dispersal particularly relevant in the context of invasions
- What brings individuals to the new area in the first place à Dispersal also key for metapopulations (“a population of populations”)
Emigration dispersal is commonly density-dependent
- Commonly triggered by the more intense competition in crowded areas
- Can also go the other way: individuals leave low density patches (e.g. to avoid inbreeding)
- Regulatory effect on populations (similar to density-dependent mortality)
- Possibly the main effect of dispersal for the dynamics of single populations!
Measuring movement
- We focus on animals but movement also relevant for other organisms (e.g. seed dispersal in plants!)
- Broadly, three types of approaches:
-Individual marking
+ observation Using tracking technology
=Analyzing “intrinsic markers”
Individual marking + observation
- Information about movement from individual observations (live observation, dead recoveries)
- Need substantial observation effort, gaps in data, limitations to monitor long-distance movement
Radio-tracking
à VHF tracking
- Transmitter on animal sends VHF (radio) signal
- Researcher picks signal with portable receiver and estimates position (multiple fixes, triangulation)
- Need to be in some proximity of the animal
Satellite tracking
- Transmitter on animal sends radio signal
- Satellites pick signal, estimate location, send data to researcher
- Researcher does not need to be close to the animal
àGlobal Navigation Satellite System (GNSS
) • Device on animal uses signal from GNSS, e.g. GPS, to calculate location
- Data obtained when device retrieved. Or sent to researcher via another satellite
- Usually more accurate than satellite tracking (but devices may be heavier)
Geologgers
Devices measure light levels at regular times and store data
- Once device retrieved, data used to estimate location by inferring solar position with respect to horizon
- Not very accurate, but light weight!
Intrinsic markers
- Origin of individuals may be identified by looking at e.g.
- Stable isotopes
- Genetic markers
- Trace elements
- Species assemblages of parasites
Many methods, different pros/cons of tracking
• Need to handle animal? • Accuracy of information • Devices: trade-off between the size of the device, its price and its data collection capacity • But technology is advancing fast!
What is a metapopulation?
“A population of populations”
In a metapopulation:
- Local populations occupy discrete habitat patches surrounded by unsuitable habitat
- There is movement of individuals among subpopulations
- Habitat patches are not necessarily all occupied at any given point in time
- Subpopulations may go extinct, and later be recolonized
The dynamics of the metapopulation as a whole are determined in large part by the rate of extinction of individual subpopulations, and the rate of colonization by dispersal of uninhabited patches
Examples of metapopulations
à Glanville Fritillary butterfly (Melitaea cinxia), inhabiting meadows in the Aland Islands in Finland
à Mountain sheep (Ovis canadiensis) populations in southern California, inhabiting mountain tops surrounded by unsuitable flat desert
Can also find metapopulation in species inhabiting discrete water bodies (lakes, ponds…) • Amphibian populations connected by seasonal dispersal through the landscape • Plant/invertebrate populations may be connected as birds transport propagules between waterbodies à Growling grass frog (Litoria raniformis) in wetlands around Melbourne
Metapopulation dynamics
In a ‘classic’ metapopulation:
- Suitable habitat only found in discrete patches
- Subpopulations have a risk of extinction
- Patches can be recolonized
- Dynamics of subpopulations largely independent (i.e. not synchronous; driven by local factors ) So that when on subpopulation goes extinct, others are thriving and can generate dispersers to recolonize the empty habitat patches Correlated extinctions (driven by regional factors) can sharply reduce the expected persistence time of the system
- Habitat patches may vary in size, quality, and isolation from other patches
- All of these factors influence how many individuals move among the subpopulation
Metapopulation dynamics patch size
- In “classic” metapopulations: patches of similar characteristics, roughly equal probability of extinction “classic” metapopulation
- In real systems there may be substantial variation in the size and/or quality of habitat patches à
Sources: large/high quality patches; extinction unlikely; source of dispersers (“donor” patches)
à Sinks: small/low quality patches; frequent extinctions and recolonization (“receiver” patches)
Models of metapopulations
- Metapopulation dynamics can be studied with mathematical models (not covered in this subject)
- Range from simple deterministic models, with strong assumptions about extinction and colonization…
- … to more realistic stochastic models based on simulation that:
- Account for stochasticity in extinction and colonisation (similar to accounting for demographic stochasticity)
- Account for factors that affect extinction and colonization rates (environmental factors, patch characteristics)
Implications for conservation (metapopulation)
- Many threatened species only remain in separate, often small, populations
- No single population may guarantee long-term survival… but the combination of several populations may do!
- Important to preserve or enhance connectivity Concepts and models of metapopulation dynamics can help: - Assess viability of populations of threatened species - Choose suitable designs for reserves and corridors - Identify suitable management strategies
What is a life history?
• Pattern of survival and reproductive events for a species
Why do life histories look so different between species?
• Life history patterns are an “optimization” of tradeoffs between growth, survival, and reproduction.
Fecundity and parental investment
- Fecundity is an organism’s reproductive capacity (the number of offspring it’s capable of producing).
- Parental investment is the energetic investment into each offspring (e.g. egg size, seed size, amount of parental care)
- “Quantity versus quality” tradeoff between number of offspring and a parent’s energetic investment in the individual offspring.
- Organisms can have many offspring each with a small energy investment, or few offspring each with a large energy investment.
Fecundity and parental investment example
- e.g. Atlantic cod produce millions of eggs which drift freely in the ocean and larvae have to fend for themselves.
- In contrast, mouth-brooding cichlid fish produce relatively low numbers of eggs and then protect their young from predation by hiding them within their mouth.
- Elephants have long gestation, large young, and a long period of parental care for each offspring.
experiment to show that Parental care is costly
- Researchers in the Netherlands tested the effects of parental caregiving in Eurasian kestrels over five years.
- They transferred chicks among nests to produce reduced broods (three or four chicks), normal broods (five or six), and enlarged broods (seven or eight). They then measured the percentage of male and female parent birds that survived the following winter. (Both males and females provide care for chicks.)
- The lower survival rates of kestrels with larger broods indicate that caring for more offspring negatively affects survival of the parents.
- Same broad patterns also seen in plants.
- Plants produce either large numbers of energetically “cheap” seeds or small numbers of energetically “expensive” seeds
Age at maturity
- Early reproduction strategy: short-lived, small in body size. Strategy is geared towards early energy going toward reproduction rather than growth.
- Reduces the risk of not reproducing at all
- Late reproduction strategy: long-lived, larger in body size. Strategy is geared toward putting energy into growth to a larger size where mortality rates are lower, then later in life insetting energy in reproduction. Often a strategy that allows significant parental care of offspring.
- Strategy carries a higher risk of not reproducing at all or to maximum capacity if death occurs early.
Single vs. multiple reproductive events
Semelparity and iteroparity are two types of possible reproductive strategies
. A semelparous species is characterized by a single reproductive event before death. Semelparity comes from the Latin semel ‘once’ and pario ‘to beget’.
An iteroparous species is characterized by multiple reproductive events throughout its lifetime. Iteroparity comes from the Latin itero, ‘to repeat’, and pario, ‘to beget’.
r-selected species
(density independent)
- high rates of fecundity
- short gestation
- low levels of parental investment in the young
- high rates of mortality before individuals mature
K-selected species
s (density dependent)
- low rates of fecundity
- high levels of parental investment in the young
- low rates of mortality of mature individuals
R-selected species can undergo population booms and busts
- African locusts – an r-selected species which undergoes population booms in response to good environmental conditions (abundant food)
- The life history strategy of the locust makes this population boom possible. Females mature early (at 1-6 months of age depending upon conditions, a female can lay 100 eggs at a time, and they have a short lifespan of 3-6 months. 2-5 generations per year are possible.
- All this means that a 10-16 fold increase in numbers are possible from one generation to the next. At that rate of increase, an initial swarm of just 10000 locusts can create a swarm of 100 billion locusts in just seven generations within less than 2 years.
Population stability and fluctuation
Fluctuations can occur for biotic and abiotic reasons
Population cycling at regular intervals also possible in natural populations e.g. hare and lynx populations go through peaks and troughs on a roughly 10- year cycle. Most likely cause is predator build-up as hare populations increase, leading to hare overexploitation and a crash in their populations followed by a crash of the predators.
Parasite
– An organism that obtains its nutrients from a host or very few hosts, normally causing harm to the host but not necessarily causing death. Parasites are “predators that eat prey in units of less than one
Infection
When parasites colonise a host, the host harbours an infection
Disease
If an infection causes symptoms in the host, then the host has a disease.
Pathogen
Any parasite that causes a disease is called a pathogen
Vector
– An organism which carries and transmits an infectious pathogen into another organism
Virulence
– The severity or harmfulness of a disease.
How many parasites are there?
Lots!
- Organisms in natural habitats usually have one or more parasites
- Many parasites only have one host, or a very limited number of hosts (host specificity)
Parasites are very common – more than 50% of the species on earth, and more than 50% of individuals are parasites!
Micro-parasites
- Small and often intra-cellular.
- Multiply directly within their host.
- Often extremely numerous
Macro-parasites
- Grow on or in but do not multiply on their host. Unlike microparasites.
- Produce infectious stages which they release into the environment to find new hosts.
- Often live on the body or in the body cavities (e.g. the gut/intestine) rather than being intra-cellular.
e.g. helminths, nematode worms, tapeworms, copepods, lice, fleas, ticks, mites
How are parasites transmitted?
- Directly transmitted parasites do not require a vector to reach their hosts. They include parasites of vertebrates such as lice, mites, copepods, amphipods, monogeneans; and many species of nematodes, fungi, protozoans, bacteria, and viruses.
- Trophically transmitted parasites are eaten by hosts. When eaten, they survive digestion and mature into their adult form. They often have complex life cycles with one or more intermediate hosts. They include trematodes (all except schistosomes), cestodes, acanthocephalans, pentastomids, many round worms, and many protozoa. They have complex life cycles involving hosts of two or more species. They can alter intermediate host behaviour so they have a greater chance of being eaten.
- Vector-transmitted parasites are carried by other organisms between their hosts. They are microparasites, such as protozoa, bacteria, or viruses. Fleas, lice, ticks, and mosquitoes are the most common vectors.
What kinds of strategies do parasites have?
- Parasitic castrators reduce or remove their host’s reproductive ability and use the energy that would have gone into host reproduction for parasite growth. The host survives and sustains the parasite.
- Parasitoids are insects which eventually kill their hosts. Most parasitoids are hymenopterans, parasitoid wasps; others include dipterans such as phorid flies. Parasitoids either 1) sting their large prey, carry it to a nest and lay an egg on top which hatches and feeds on the prey, or 2) lay their eggs directly into the host. The eggs hatch and grow in the living host, eventually emerging from the host
- Micropredators attack several hosts, usually feeding on blood. Invertebrate examples include leeches, mosquitoes, flies, fleas and ticks. Vertebrates examples include lampreys, vampire bats and false cleaner fish.
- Brood parasites use other species to raise their young
To what extent are animal and plant populations affected by parasitism and disease?
The answer depends on:
- pathogen virulence
- whether the pathogen reduces host survival (death rate), reproduction (birth rate), or both.
Strong differences between microparasites and macroparasites.
Epidemic or endemic?
Pathogenic diseases can be either epidemic or endemic within populations
- Epidemic diseases are characterised by rapid changes in the prevalence of infection.
- When outbreaks occur, these pathogens cause waves of infection that can cause rapid population declines.
- Often such infections disappear from a particular host population for short or long periods
-Endemic infections persist for long times in populations, showing relatively little fluctuation in prevalence.
Epidemics can cause mass mortalities
The Black Death affected Europe during the Late Middle Ages.
Caused by the bacteria Yersinia pestis and transmitted by fleas of several species in the wild and of rats in human society.
Estimated to have killed 30% to 60% of Europe’s population. In total, the plague may have reduced the world population from an estimated 475 million to 350–375 million in the 14th century
who usually dies in an pandemic
The elderly, those who were impoverished, and those who had suffered relatively poor health faced higher risks of death during the epidemic than their younger, wealthier, and healthier peers.
What happened after the epidemic?
- Increased resources available to those that survived.
- Population grew at a greater rate after the epidemic than before.
Endemic parasites can suppress populations
Micro- and macro-parasites that don’t kill their prey can affect:
- Birth rates 2. Death rates, via increased predation 3. Movement (immigration and emigration)
Can disease cause populations to go extinct?
- Pathogens are more likely to cause host extinctions if they exhibit frequency-dependent transmission (i.e. transmission rate is similar regardless of population size), have long-lived infectious stages, or infect multiple different host species.
- This means that they can be transmitted between common reservoir hosts and species that may have small population sizes. These three traits allow for persistent transmission (and decreased host fitness) even when a host is at low abundance.
- Partula turgida was a species of air-breathing tropical land snail. This species was endemic to Ra’iātea, French Polynesia. It died out in 1996 and is now extinct.
- Investigations of the last surviving individuals showed infection with a protozoan parasite as the cause of death. The parasite was a microsporidian (Steinhausia). which causes mortality in other snails.
Strategies for disease prevention and control of microparasites
- Culling (of infected animals and plants, and disease vectors)
- Behavioral modifications including quarantine and social distancing
- Vaccination (e.g. measles)
Virulence-transmission trade-off hypothesis
Parasites depend on their hosts for survival and transmission, they should evolve to become benign, yet many parasites cause harm. Theory predicts that parasites could evolve virulence (i.e., parasiteinduced reductions in host fitness) by balancing the transmission benefits of parasite replication with the costs of host death. This is known as the virulence-transmission trade-off hypothesis.
Virulence can change through time. Initially high, evolving towards intermediate virulence to ensure ongoing transmission.
Hosts can also evolve in ways that influence virulence
Host tolerance - the ability of a host to tolerate infection with a pathogen by minimizing the damage done but without impeding replication or transmission of the pathogen.
Host resistance – the ability of a host to reduce the probability that it is infected, reduce pathogen replication within the host, and/or increase the speed of pathogen clearance (recovery)
threatened species
-Species that are on the pathway to extinction
Current number of threatened species
-More than 32000 species are threatened which is 27% of all assessed species
Key characteristics of threatened species populations
• Small population size
- Possible Allee effects
- Low genetic diversity
- Small geographic ranges
- Slow growing and reproducing
- Narrow ecological niches
What is an Allee effect?
Allee effects are a small population phenomenon in which population growth rate is reduced by undercrowding (low population density).
Allee effects are widely believed to be common and are important for conservation efforts. Even if threats that caused the decline to a small population are removed, a population may not recover from a strong Allee effect.
The most commonly observed mechanism that causes an Allee effect is mate limitation. e.g. too few animals in an area to discover mates or too few plants close enough to achieve pollination
Can also occur through cooperative defense, predator saturation, cooperative breeding, cooperative feeding or dispersal.
Allee effect via mate limitation
- Tree has a typical dispersal range for its pollen (blue circle). When trees are clustered and population size is large, pollination occurs.
- Habitat loss causes population decline. Trees become less clustered. Many trees are no longer able to be pollinated as they are too distant from their neighbour
Low genetic diversity
- In small populations, matings between relatives are common. This inbreeding may lower the population’s ability to survive and reproduce, which is called inbreeding depression.
- Lower genetic diversity leads to lowered evolutionary potential, compromised reproductive fitness, and elevates extinction risk. A small population of adders experienced inbreeding depression when farming activities isolated them from other populations.
- Higher proportions of stillborn and deformed offspring were born in the isolated population than in the larger populations.
Small geographic ranges
- Species with small geographic ranges have a higher risk of extinction than species which are widespread.
- Small ranges expose species to greater threat of habitat loss as the threatening process may occur across the entire range of the species
- Catastrophic population declines may occur after severe events, such as fire, storms, floods etc.
- E.g. The mountain pygmy possum is restricted to just three mountain top habitats in the Australian alps, typically above 1600 m in altitude
Slow reproductive rate
- Species with slow reproductive rates have higher the risk of extinction than rapid breeders. Population growth rates may be too slow to counter a population in decline from threats.
- e.g. the kakapo, a large, ground-dwelling parrot. It is critically endangered with only 209 adults confined to four islands off the coast of New Zealand. Kakapo are long-lived, with an average life expectancy of 60. The female kakapo lays 1–4 eggs per breeding cycle. Eggs hatch after 30 days. The female feeds the chicks for three months, and the chicks remain with the female for some months after fledging.
- Males and females start breeding between 5-9 years of age. Kakapo do not breed every year and has one of the lowest rates of reproduction among birds.
Narrow ecological niches
- Species with narrow ecological niches are more vulnerable to extinction than those with broad nicehs
- Ecological niche: the position of a species within an ecosystem, describing both the range of conditions necessary for persistence of the species, and its ecological role in the ecosystem.
- A narrow ecological niche means a species relies heavily on specific habitats or resources within an ecosystem. e.g. mountain pygmy possum awake from hibernating under the snow for 7 months. They rely heavily on the highly nutritious and abundant bogong moths which migrate to the mountain tops in summer
Threats to threatened species
Globally (100000+) Around the world the top two impacts on threatened species are habitat loss and change due to agriculture, closely followed by overexploitation activities, such as hunting or timber harvesting.
Australia (1500+) The top factors impacting Australia’s threatened species are invasive species and changes in habitat.
Habitat loss and degradation
Changes to habitat include broadscale loss of habitat due to clearing for agriculture, forestry, urbanization, altered fire patterns and degradation from other human activities
Shrinking habitats, shrinking populations
Overexploitation
Large, slow reproducing species are particularly vulnerable to overexploitation. Collections of animals and plants for food, medicines, pet trade
Invasive species
- Invasive species include pest animals, plants and diseases.
- Impact populations via predation, competition for space and resources, or by causing mortality through toxicity.
- Since European settlement there have been devastating effects on Australia’s terrestrial mammal fauna 22 species of native mammals have gone extinct from Australia and 100 spp. are threatened. 10% of mammal fauna are now made up of invasive species
Multiple threats
- When threats are additive, they can cause spectacular declines.
- Passenger pigeons on the US prairies declined from a population of many billions in the early 1800s to extinct in the wild in 1901.
- Decline was likely due to habitat loss plus overexploitation.
Conservation interventions to restore populations method
- Habitat restoration
- Remove single threat - overexpolitation
- Population boosting
- Genetic rescue
Habitat restoration
Creation of reserves (e.g. national parks, marine protected areas) e.g. Great Barrier Reef Marine Park has conservation zones to reduce threatening activities
Reducing exploitation levels
Removal of invasive species – predators and competitors
Population boosting
Captive breeding to increase population numbers before release back into the wild release
Might be coupled with other strategies (e.g. threat reduction)
e.g. many native Australian mammals (e.g. bilbies, numbats, bettongs, bridled nail-tail wallabies, hare wallabies) and the Lord Howe Island stick insect
Genetic rescue
- Genetic rescue is the process where inbred populations receive genes from another population such that their overall genetic diversity increases.
- In a conservation sense, genetic rescue tries to solve the problem of inbreeding depression, where too many individuals mate with close relatives because the population is small.
- The consequences of inbreeding depression are reduced biological fitness (fertility, survival, longevity, etc.)
Mountain pygmy possum case
- 3 regions (northern, central, southern)
- genetically isolated (>20,000 yrs)
- Mt Buller population discovered in 1996
- population entirely within resort boundaries
- Population & genetic decline in mount buller
- By 2009, captive breeding had not succeeded
- • Population was predicted to go extinct within 3-5 years
- • Developed a “genetic rescue” strategy
- • Males from a nearby population released into the Mt Buller population
- Population increase Genetic variation restored
