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Flashcards in surveys and monitoring (lecture 7) Deck (20)
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Point-in-time surveying:

- why survey?

1. look at single site
- new species, management plan, impact assessment

2. compare multiple sites
- biodiversity, habitat type/condition, status of key species

surveys essential for conservation planning
- need fine scale distribution data
- expensive but cost effective

romeo error
- surveys can rediscover species thought to be extinct


What is monitoring?

- regular repeat surveys to measure change

- used to quantify loss & impacts, identify causes and identify counter strategies


What are monitoring targets?

- same as surveys: species richness, habitat condition etc

- plus additional: demography, phenology etc


Biases in UK surveys:

- breeding birds
- plants


breeding birds:
- breeding success & population size monitored annually
- distribution only 3 times since 60s

- breeding success not monitored at all
- population size monitored annually for some rare
species, otherwise haphazard
- distribution monitored twice since 1960s, but

there are also geographic biases


Why do surveys and monitoring share core principles?

- monitoring is a repeat survey
- good survey design allows for future repeats


What is accuracy?

- how close estimate is to truth
- inaccurate results are biased

- difficult to assess accuracy but possible to assess if survey methods likely to create bias
- bias usually arises from inappropriate site selection/counting methods


What is precision?

- how close different estimates are to each other
- unrelated to true value

- easy to assess: 95% confidence intervals/standard errors

- precision increases with increased sample size and reduced variation within the sample


What are the core principles of designing surveys/monitoring schemes?

1. Define objectives
- realism vs ambition

2. Define study area
- can be difficult

3. Choose survey locations
- avoid bias:
- systematic, random, or random stratified sampling

4. Minimise all other sources of variation
- observer quality: training & clear guidelines
- weather: only suitable conditions
- time of day/season: keep constant
- effort: keep constant


What is:

- systematic sampling?
- random sampling?
- random stratified sampling?

systematic sampling:
- sampling in a prespecified pattern from starting point
- prespecified pattern may match ecological variation therefore creating bias
- not ideal

random sampling:
- equal probability of selection
- can miss rare habitat types

random stratified sampling:
- increases surveying of rare habitat types
- random sampling of sites within categories e.g. habitat type
- decreases sampling where variation is low e.g. where focal species unlikely to occur


Methods: assumptions and common problems

- territory mapping

- multiple visits to site
- record location/activity of all sightings of an individual
- define clusters of sightings
- clusters = territories

- excellent technique for an appropriate species
- time consuming
- doesn't work for colonial species (e.g. meerkat), polyterritorial species (e.g. wood warbler), species whose habitats can't be detected


Methods: assumptions and common problems

- mark and recapturing/resighting

- population size estimated from number of marked individuals recaptured/sighted in a subsequent sample

- depends on whether populations are closed or open
- e.g. influence from mortality, immigration, emigration, recruitment

- labour intensive but great for elusive species
- camera traps for large animals
- pit fall traps for small mammals/reptiles


What types of marks are used for mark/recapture surveys?

- e.g. natural markings on coat, scars etc

- temporary e.g. fur clipping, toe clipping
- permanent e.g. pit tags


What method to use when designing mark-recapture in an open population?

- jolly-seber method

- key assumptions:
i) marks last during the sampling period
ii) capture probabilities are constant across
iii) emigration losses are permanent


Methods: assumptions and common problems

- transects and point counts?

- previous methods are complicated & time
- counting all individuals detected in an area simpler

- transect: route along which focal species occurrence is recorded
- point count: transect with length of 0


What are the core assumptions of transects/point-counts?

- all individuals exactly on the route are
- individuals do not move before detection
- individuals are not ‘double-counted’
- individuals are detected independently
- distances measured accurately


Transect or point-count?

transects generally better
- more individuals counted per unit time when moving along a transect

point counts good when:
- habitat is fragmented
- access difficulties lead to route diversion/difficulties moving and counting simultaneously


What can transects/point-counts be used for?

- can calculate an index of population trends


- can't compare densities b/w species/habitats
- can't calculate population size


What are issues with detectability with transects/point-counts? How is this resolved?

- detectability declines with distance from transect
- declines closer for elusive species/in dense habitats
- declines further for conspicuous species/in open habitats

- distance samplings corrects for detectability variation by estimated number of undetected individuals
- allows for estimation of absolute density estimates


Methods: assumptions and common problems

- botanical surveys?

- all general design principles apply to plants
- territory mapping & mark/recapture
- can use distance sampling, e.g. cacti, need to take plant size into account


How to survey small plants?

- usually via quadrat
- ideal quadrat size = trade off b/w sample size and time taken per quadrat
- usually measures % plant cover not individuals