surveys and monitoring (lecture 7) Flashcards Preview

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Flashcards in surveys and monitoring (lecture 7) Deck (20)
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1
Q

Point-in-time surveying:

  • why survey?
A
  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

2
Q

What is monitoring?

A
  • regular repeat surveys to measure change

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

3
Q

What are monitoring targets?

A
  • same as surveys: species richness, habitat condition etc

- plus additional: demography, phenology etc

4
Q

Biases in UK surveys:

taxonomic

  • breeding birds
  • plants

geographic

A

breeding birds:

  • breeding success & population size monitored annually
  • distribution only 3 times since 60s

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

there are also geographic biases

5
Q

Why do surveys and monitoring share core principles?

A
  • monitoring is a repeat survey

- good survey design allows for future repeats

6
Q

What is accuracy?

A
  • 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
7
Q

What is precision?

A
  • 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
8
Q

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

A
  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
9
Q

What is:

  • systematic sampling?
  • random sampling?
  • random stratified sampling?
A

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
10
Q

Methods: assumptions and common problems

  • territory mapping
A
  • 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
    BUT
  • time consuming
  • doesn’t work for colonial species (e.g. meerkat), polyterritorial species (e.g. wood warbler), species whose habitats can’t be detected
11
Q

Methods: assumptions and common problems

  • mark and recapturing/resighting
A
  • 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
12
Q

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

A

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

artificial:

  • temporary e.g. fur clipping, toe clipping
  • permanent e.g. pit tags
13
Q

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

A
  • jolly-seber method
  • key assumptions:
    i) marks last during the sampling period
    ii) capture probabilities are constant across
    individuals
    iii) emigration losses are permanent
14
Q

Methods: assumptions and common problems

  • transects and point counts?
A
  • previous methods are complicated & time
    consuming
  • counting all individuals detected in an area simpler
  • transect: route along which focal species occurrence is recorded
  • point count: transect with length of 0
15
Q

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

A
  • all individuals exactly on the route are
    detected
  • individuals do not move before detection
  • individuals are not ‘double-counted’
  • individuals are detected independently
  • distances measured accurately
16
Q

Transect or point-count?

A

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
17
Q

What can transects/point-counts be used for?

A
  • can calculate an index of population trends

BUT

  • can’t compare densities b/w species/habitats
  • can’t calculate population size
18
Q

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

A
  • 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
19
Q

Methods: assumptions and common problems

  • botanical surveys?
A
  • all general design principles apply to plants
  • territory mapping & mark/recapture
    irrelevant
  • can use distance sampling, e.g. cacti, need to take plant size into account
20
Q

How to survey small plants?

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