Declining Population Paradigm

Question 1

Differences between SPP and DPP

Answer 1

Population size - but continuum between the two
-some form environmental change driving pop decline - beneath threshold and SPP kicks in
SPP rich in theory promoting local intensive management
DPP tries to detect declines, identify cause and prevent
-less rich in theory
-more proactive

Question 2

Applying DPP to already small populations ?!?!

Answer 2

Spoon-billed sandpiper - low population anyways, now dropping 3000 to <200
Caused by…
1. Low breeding success - disturbance or predation
2. Large scale winter habitat loss
3. Low recruitment due to hunting etc.
-no evidence of SPP

Question 3

SPP and DPP acting together

Answer 3

Atitilan Grebe
Exotic fish causes comp for inverts + reed cutting (loss of food and habitat) = pop decline
Conservation efforts to help both - increased pop
Earthquake struck = smaller lake + new grebe spp which caused hybridisation = further decline
All acting at once = synergistic impact, hard to identify cause and reverse decline

Question 4

Finding a declining population

Answer 4

Need to be aware of populations declining to help
Not always possible as lots of IUCN are data deficient (10% mammals, 24% amphibians)
Methods:
1. Using data collected by naturalists
2. Interviews with local popultions
3. Spatial variation in factors that drive declines
4. Biological correlates of vulnerability

Question 5

Data from naturalists…

Answer 5

Use sightings to record no. of sighting per unit hours, or something similar
Has revealed great white shark population crashes on certain coats

Question 6

Interview with local populations…

Answer 6

If they interact with wildlife a lot that is

Need to consider shifting baselines - young people can’t see a decline they haven’t witness (bias)

Question 7

Spatial variation in factors that drive declines

Answer 7

Not all are evenly distributed, including…

1. Habitat loss
2. Over-exploitations
3. Introduced species

Question 8

Biological correlates of vulnerability

Answer 8

Ecological and life history traits that will make a species more vulnerable to population declines
e.g. declines don’t always follow habitat loss, so need to consider more
Body size - larger bodied, longer lived, less offspring etc. hard to adapt
Brain size - changes in behaviour to adapt
Combine with environmental factors for more powerful predictions

Question 9

Causes of declines

Answer 9

Demographic causes - reduced survival or breeding success etc.
Environmental causes behind this

Question 10

Species recovery curve

Answer 10

1. Monitoring
2. Diagnosis
3. Solution testing
4. Deployment
5. Sustainable management

Question 11

Diagnosis strategies

Answer 11

1. Complete simulation model
   - like population viability analysis (PVA) but needs lots of data (too much)
2. Comparative approach - list any causes the may cause decline, identify populations which differ in environmental conditions in time (monitoring data) or space (2 different populations)

Question 12

Comparative approach examples

Answer 12

Corncrakes decline…
-correlated with change of machines starting to cut hay at 60% with the 1:1 line of equivalence
Also compare populations in areas with different environments (if no pre or post decline info)
Corncrakes showed link of presence of hay meadows with retained and lost pops

Question 13

Comparative approach problems

Answer 13

1. Often multiple factors change in environments at the same time - hard to isolate one
2. Often have insufficient monitoring to link population declines to data from e.g. 10yrs ago
3. Spatial scale and environmental monitoring can differ
4. Time lags distort relationships, so may appear stable when the environment first changes - like breeding season

Question 14

Correlation doesn’t mean causation (methods to avoid)

Answer 14

1. Check individual movements of study spp - declines in pops of certain habitat, may be vacating to better habitat
2. Test for all possible causes of decline - not always possible by lack of data, incorrect diagnosis by testing 1 hypothesis, often ignores disease here too
3. Check the proposed cause alters demography, and check data over years - whats limiting a pop can change
4. Check with experiments - PVA could be useful here (determine features for optimum management of spp)

Question 15

Solution testing

Answer 15

Experiments useful here
E.g. Linum cratericola (plant) - critically endangered by grazing by goats and competitor (exotic shrub)
E.g. skylark plots - improves foraging as no winter wheat, could reverse pop decline and made economically profitable for farmers but wouldn’t do it