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APS271 Conservation Principles > declining population paradigm (lecture 6) > Flashcards

declining population paradigm (lecture 6) Flashcards

1
Q

What are the differences between the small and declining population paradigms?

A
  • continuum, relative importance of factors shift over time

small population (SP):

  • rich in theory
  • promotes local & very intensive management
  • firefighting
    e. g. vaquita: < 30 individuals

declining population (DP):

  • less rich in theory
  • general principles concerning diagnosis and management of causes of decline
  • less intensive management over larger areas
  • proactive
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2
Q

What is an example of the declining population paradigm affecting small populations?

A

Spoon-billed sandpiper (CE)

  • previously 3000 pairs now <200
  • low breeding successes: disturbance and predation
  • large scale winter habitat loss
  • low recruitment: hunting

i.e. not yet experiencing stochasticity, inbreeding, allee effects

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3
Q

How can small and declining population paradigms act together?

  • Atitilan grebe
A

factors driving decline change over time:

  • DPP: habitat destruction, exotic species
  • SPP: earthquake, hybridisation
  • multiple factors interact (can be synergistic)
  • diagnosing & thus reversing causes of decline is essential, but difficult
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4
Q

What are difficulties with declining populations discovery?

A
  • difficult due to geographic or taxonomic biases in monitoring
  • many species are data deficient
  • need to exploit other methods
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5
Q

How are declining populations discovered?

  • naturalist recordings
A
  • haphazard naturalists’ recordings can reveal past population sizes/population crashes
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6
Q

How are declining populations discovered?

  • local people
A
  • interviewing local people e.g. fisherman can give accurate idea of population declines if shifting baselines taken into account
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7
Q

How are declining populations discovered?

  • spatial variation in factors driving decline
A
  • look for areas where factors driving decline are intense

e. g. habitat loss, over-exploitation, introduced species

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8
Q

How are declining populations discovered?

  • biological traits
A
  • idea that ecological and life history traits predispose species to population declines in response to human activities

e.g. body size
- hunting
- bigger animals mean
more food
- reproduction
- bigger animals have a
slower growth rate

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9
Q

What are the weaknesses of using biological traits to identify declining populations?

A
  • Collen et al., 2011
  • species traits weaker predictors than environmental traits
  • Fritz et al., 2009
  • geographic transferability is limited
  • body size only a good predictor in the tropics
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10
Q

What is meant by the cause of a decline?

A
  • demographic causes
    e. g. reduced surival/breeding success/recruitment
  • environmental causes
    e. g. poisoning from DDT/pesticides
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11
Q

How to diagnose cause of a decline?

  • simulation model
A

Population Viability Analysis (PVA)

  • requires knowledge of relationship between demographic traits & all external factors
  • for most species, knowledge barrier too great to implement with sufficient speed
  • need plenty of data
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12
Q

How to diagnose cause of a decline?

  • comparative approach
A
  • list plausible factors for decline
  • identify populations that differ in these environmental conditions through time/space
  • allows environmental factors causing decline to be identified
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13
Q

How to diagnose cause of a decline?

  • comparative approach: timing
A
  • compare timing & decline of environmental change

e. g. dramatic corncrake decline when machine cutting of hay (vs hand cutting) reaches 60%

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14
Q

What are problems with comparing timing?

A

several environmental factors often change simultaneously
- e.g. agricultural intensification
- more machinery/chemicals/hedge
removal/higher stocking densities

monitoring is too infrequent to
identify precise timing of change in environment or population decline,
e.g. many plants
- spatial scale of population &amp;
environmental monitoring differ
e.g. fish stocks &amp; marine wildlife
- time lags can distort relationships
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15
Q

How to diagnose cause of a decline?

  • comparative approach: different environments
A
  • use when not possible to compare populations pre and post decline
  • can compare declined populations with undeclined populations at other sites

BUT

correlation does not always = causation
- positive correlation between rat poison & rat population doesn’t mean poison isn’t good for rats

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16
Q

How to diagnose cause of a decline?

  • comparative approach: different environments - radiated tortoise
A 
Radiated tortoise:
- madagascan endemic
- harvested for food &amp; pet
trade, pop thought to be
declining
- trade bans, but no
evidence that trade was
causing the decline

compared densities in commercial areas (1 per km2) and remote sites (2500 per km2)

supporting evidence:

i) densities increase with distance from urban areas
ii) commercial hunters travel increasing distances c.200 km

17
Q

How to diagnose cause of a decline?

  • check for individual movements: great tits
A
  • say in first year 50 tits in woods, 50 in hedgerows
  • second year 50 tits in woods, 10 in hedgerows
  • does this mean hedgerows have declined in quality?
  • not necessarily true
  • buffer effect: if habitat quality varies then highest quality sites will be occupied first & abandoned last
  • if tits prefer woods & can move between woods &
    hedges then any factor that drives a population
    decline (e.g. a cold winter) will result in greater pop
    decline in hedges
18
Q

How to diagnose cause of a decline?

  • test for all possible causes of decline
A
  • rarely possible due to lack of data
  • common problem is
    lack of information from
    non-breeding grounds of
    migrants
  • need to acknowledge bias
19
Q

How to diagnose cause of a decline?

  • test for all possible causes of decline: albatross
A
  • many studies only test the
    favoured hypothesis
  • can lead to incorrect
    diagnosis

Rolland et al., 2009
- albatross all threatened by long-line fishing
BUT
- in Indian yellow nosed albatross, cholera is more important

20
Q

How to diagnose cause of a decline?

  • test for all possible causes of decline: New Zealand birds
A
  • major declines in NZ native birds: introduced
    predators & associated factors
  • disease ignored: avian malaria equally likely as
    causal agent
  • major factor on other islands, present in introduced &
    native birds & known to cause mortality
21
Q

Recovery case studies:

  • Linum cratericola
A

critically endangered

  • discovered at 2 sites in 1966
  • extinct at 1 sites invaded by an exotic shrub
  • also a large number of feral goats

hypothesis that grazing invasion causing decline

  • 1997
  • 2 groups of plants enclosed in goat-proof fence & invasive shrub cleared
  • intensive goat control in general area
  • population size increased until goats broke into enclosure
  • often need to manage more than 1 threat to a species
22
Q

Recovery case studies:

  • skylark
A 
1970-2008:
- decline of 53%
- almost all of decline on
farmland
- higher productivity on
spring sown cereals than
winter cereals
- reduced food availability
  • skylarks struggle to forage in tall thick winter cereals
  • leaving undrilled patches in winter cereal fields
  • fields w 2 skylark plots per herctare have significant benefits
  • mostly use them for foraging but increases breeding success
  • more chicks, heavier chicks

APS271 Conservation Principles (20 decks)

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