Unit 2.5 Investigating Ecosystems Flashcards
Investigating ecosystems
Organisms in an ecosystem can be identified using a variety of tools, including keys
Biological key
chart that is used to identify organisms and
deduce their correct species.
Methods to measure abiotic factors
Marine ecosystems
- salinity
- pH
- temperature
- dissolved oxygen
- Wave action
Freshwater ecosystems
- turbidity
- pH
- temperature
- dissolved oxygen
Terrestrial ecosystems
- Wind speed
- Light intensity
- temperature
- slope
- Soil moisture
Light intensity
Instrument used: light meter
Why measure it?
Light intensity influences the productivity of
producers and therefore the availability of
energy in the entire ecosystem.
Important:
The fact that light intensity varies with time
(sunny period, clouds, time of the day,
season) should be taken into account.
Turbidity
Instrument used: Secchi disc.
Why measure it?
Turbidity limits the penetration of sunlight and
thereby the depth at which photosynthesis can
occur.
Important:
Problems can arise due to the Sun’s glare on the
water, or the subjective nature of the measure.
Wind
Instrument used: digital anemometer. You
can also observe the effects of wind on
objects and relate it to the Beaufort scale.
Why measure it?
- monitoring and predicting weather patterns and global climate.
Important:
- Care must be taken not to block the wind.
- Gusty conditions may lead to large
variations in data.
Estimating the abundance of organisms
Motile organisms
1. Direct method: actual counts
2. Indirect method: capture-mark, recapture (Lincoln index)
Non-motile organisms
1. Actual counts with quadrats
2. Population density
3. Percentage cover
4. Percentage frequency
Weaknesses of measuring abiotic components
- Abiotic factors fluctuate daily and seasonally, making brief field sampling less effective.
- Conditions like temperature and humidity can change rapidly, requiring extended observation for accurate data.
- Provide continuous, long-term data, offering a more accurate picture of environmental conditions.
- Continuous monitoring leads to results that better reflect the true state of the study area.
- Multiple samples over time increase the reliability of the data collected.
Lincoln index
It provides an estimate of the number of mobile species living in a chosen area.
formula: N = (n^1 * n^2) / m
N = total population size of animal studied
n^1 = number of animals captured on the 1st day
n^2 = number of animals recaptured on the 2nd day
m = number of market animals when recapturing on 2nd day
Safe harmless techniques to catch
small animals (mainly insects)
- Pitfall traps
- Sweep nets
- Tree beating
Quadrat sampling
All individuals in a fixed number of quadrats are counted and the data is used to calculate the abundance or percentage cover for the whole area.
Data can provide different measures of species abundance:
- Population density (number of species per unit area)
- Percentage cover (percentage of the total area within a quadrat which is covered by the species of interest)
- Percentage frequency (percentage of the total number of quadrats sampled that a particular species is found in)
Simpson Diversity Index
Allows us to quantify the diversity of a habitat or ecosystem.
DI = N (N-1) / Sum n (n-1)
N = total number of individuals collected
n = number of individuals in a species
Estimating the biomass of trophic levels
Biomass Calculation: Indicates total energy in a living being or trophic level, excluding water content for dry weight biomass.
Why Exclude Water: Water varies among organisms, contains no energy, and is not organic.
Measurement Process: Sampling organisms, drying, and weighing on an electronic balance.
Sampling Method: Random sampling for various trophic levels and recording organism numbers.
Estimation vs. Precision: Estimates are common due to errors in sampling and measuring, particularly for small organisms like algae and invertebrates.
Direct Measurement Issues: Can destroy wildlife and harm ecosystems; often replaced by using existing biomass tables.
- Despite challenges, biomass is valuable for studying energy distribution in ecosystems.
Estimating the energy of trophic levels
Measuring Energy Content: Calorimetry burns dried biomass in oxygen to measure energy in Joules.
Calorimeter Use: Common for estimating energy in foods, with ecological studies extrapolating whole organism energy from small samples.
