Investigating Ecosystems & Biodiversity

Investigating Ecosystems & Biodiversity - Key SQA Definitions : 

• Abiotic - A non-living feature of an ecosystem, such as light intensity, precipitation, temperature, wind speed, and wind direction.

• Adaptation - Any feature that makes an organism well-suited to living in its environment.

• Biodiversity - The variety that exists among living things. 

• Biological oxygen demand -  A measure of the dissolved oxygen that microorganisms consume while decomposing organic matter in a water sample. 

• Biotic - A living feature of an ecosystem, such as food supply, disease, or predation.

• Biotic index - A method for assessing the quality or health of an environment, based on the presence and diversity of organisms. 

• Capture-mark-recapture - Organisms are captured, marked and released. The ratio of marked vs not marked on recapture allows a population estimation.

• Density - The number of organisms per unit area.  

• Dissolved oxygen concentration - The concentration of oxygen dissolved in a water sample. 

• Distribution - The spatial arrangement of individuals within a population or the geographic range over which a species is found.

• Diversity index - A quantitative measure of biodiversity. 

• Ecosystem - A natural biological unit made up of living and non-living parts, ie the community and the habitat. 

• Ecosystem diversity - The different habitats, communities and environments in an area.

• Frequency - In ecological sampling, a measure used to describe how widespread a species is.

• Genetic diversity - The different genetic makeup between individuals in a species.

• Interquartile range - A measure of spread in a dataset. It is the range of the middle 50% of the data.

• Lincoln index - A statistical technique used to estimate the total population size of a species in a given area. 

• Percentage cover - The percentage of the total area of a sample site that is occupied by a particular species.

• Quadrat - A square device for taking a sample of a larger area, such as a field or beach. 

• Qualitative data -  Non-numerical information that describes qualities, characteristics, and experiences.

• Quantitative data - Numerical information that can be counted, measured, or expressed in numerical terms.

• Random sampling - A technique used to select a representative sample from a larger population where every individual or location has an equal chance of being chosen.

• Relative abundance - The abundance of an organism in an area relative to the total number of organisms.

• Reliability -  The consistency and dependability of a scientific measurement, experiment, or finding. 

• Simple random sampling - A technique where a small group is selected from a larger population or area such that every individual member, object, or location has an exactly equal chance of being chosen. 

• Simpson’s biodiversity index - A measure of diversity in a community, quantifying biodiversity by taking into account both the species richness and the abundance of each species. 

• Species - A group of organisms that can interbreed to produce fertile offspring.

• Species diversity - A measure of the number of species present within an area.

• Species richness - A measure of the number of different species represented in a specific ecological community, habitat, or region.

• Standard deviation - A statistical measure of the amount of variation or spread in a set of data values.

• Stratified random sampling - A technique used to obtain a representative sample from a population that is obviously divided into distinct subgroups. 

• Systematic random sampling - A technique that involves selecting sample locations at regular, fixed intervals after a randomly determined starting point.

• Transect - A technique used to sample along a fixed line across a location. 

• Trent biotic index - A method for assessing the water quality of rivers and streams, based on the presence and diversity of aquatic macroinvertebrates. 

• Validity - A measure of how accurate, well-founded, and reflective of the real-world phenomenon being investigated a set of results is.

Assessing Biodiversity

Ecology is the study of the relationships between living organisms, including humans, and their physical environment; it seeks to understand the vital connections between plants and animals and the world around them. 

The video below shows a summary of what exactly Ecology is:-

Ecology also provides information about the benefits of ecosystems and how we can use Earth’s resources in ways that leave the environment healthy for future generations. 

In order to understand how living organisms interact in the environment, first we need to understand how scientists describe living systems at increasingly smaller scales:-

Biodiversity

Biodiversity is a measure of the variety of living organisms in an ecosystem. Biodiversity is greater in ecosystems that provide a bigger range of different habitats and are home to larger populations of a variety of organisms, with the most biodiverse ecosystems being tropical rainforests.

Ecosystems with high levels of biodiversity help to provide the resources needed to sustain life, including human life. For example, novel medicines such as new antibiotics can be discovered in areas of high biodiversity.

The Biodiversity Intactness Index (BII) is a measure created to estimate the biodiversity loss across an area using a combination of land use, other human pressures and species abundance data to give a simple figure for biodiversity ‘intactness’  (how much nature is left from a pristine state). 

This analysis has been performed on 240 countries worldwide, with the countries ranked from highest BII to lowest. Scotland is ranked in the lowest 12% of 'biodiversity intactness' globally, with a value of 56%. This means that Scotland has lost nearly half of its original biodiversity as a result of human actions:-

Biodiversity Case Study (Terrestrial) : Cloud Forests

Cloud Forests are areas of incredibly high biodiversity, with Cloud Forests globally occupying only 0.4% of the land surface but containing about 15% of global diversity of birds, mammals, amphibians and tree ferns.

Cloud forests take their name due to the near-continuous fog and low-hanging clouds that hover around the upper canopy of the forest before condensing onto the leaves of trees and dripping onto the plants below. This causes a slower rate of evaporation and provides the plants with a continuous supply of moisture, without the need for soil.

This moisture helps to promote a huge amount of biodiversity, particularly within the type of plants known as epiphytes. These are plants which grow on other plants without damaging them, collecting their moisture and nutrients from the air, rain, and debris that surround them.

The Monteverde Cloud Forest in Costa Rica, for example, only covers an area of 105 km² (half the size of Glasgow) but is home to 3,200 species of plants, including 700 species of trees and 500 species of orchids, approximately 425 species of birds, 120 species of mammals, 60 species of amphibians and 101 species of reptiles. 

Biodiversity Case Study (Aquatic) : Coral Reefs

Coral Reefs have the highest biodiversity of any ecosystem on the planet. Coral Reefs cover less than 1% of the ocean floor, but contain more than 25% of all marine life.

Coral reefs are built by coral polyps as they create layers of calcium carbonate beneath their bodies to anchor them to the rock. The calcium carbonate that is created by hard corals provides a foundation for baby corals to settle upon, causing the reef to grow slowly in size. 

Coral reefs are found all around the globe, and are split into two groups:-

• Warm Water (Tropical) Reefs : These are found in warm oceans (growing best between 23–29°C) such as the waters off the coast of Australia. 

• Cold Water Reefs: These are found in much colder oceans (they are able to survive temperatures below -10°C), such as the Northern Atlantic around Scotland. 

You'd study the seas and oceans to help us learn more about the marine environment, plants and animals. You’d do research, for example, on the effects of climate change or the impact of pollution and offshore engineering on marine life. 

You would be planning and carrying out research expeditions, managing research projects and leading a team of researchers and technical staff, preparing scientific equipment at sea or in a laboratory and spending time at sea collecting data and samples or creating experiments to test your ideas in the laboratory. You could also use computers to produce models like maps of the ocean floor or populations of marine animals and collect data to observe and track changes in the marine environment. You’d write reports about your research for publication. You would present your findings to the public and other scientists.

Measuring Biodiversity

When a habitat is studied, it is almost impossible to count every individual that lives there. Small samples are taken which represent the whole habitat. Then the abundance of a particular species can be estimated (how many individuals there are). 

Sampling techniques include:-

• Quadrat

• Transect (line)

• Nets

• Traps (pitfall, camera + mammal) 

• Capture – mark – recapture 

There are many ways to measure organisms within a sample :- 

• Density - The total number of individuals of one species is recorded.

• Distribution - The spatial arrangement of individuals within a population or the geographic range over which a species is found.

• Frequency - How often a species features in an area.

• Percentage cover - The number of segments of the quadrat's area that a species is present within, as a percentage of the total area. Percentage cover is used when it is difficult to identify individual plants, such as grasses or moss.

• Relative abundance - The abundance of an organism in an area relative to the total number of organisms.

• Species richness - The number of different plant or animal species is recorded, but not the number of individuals within a species. 

Quadrat Sampling

Quadrats are used to sample plants and rarely, slow moving organisms such as slugs. The quadrat should be applied randomly and then the organisms within identified and counted. 

Sometimes, an organism may be partially inside the quadrat, making accurate counting awkward.  A general rule is made that if more than 50% of the organism is in the quadrat, it is counted:-

Simpson's Diversity Index

Once the base data has been gathered, statistical analysis of the data can be performed. For terrestrial (land-based) sampling, Simpson's Diversity Index is the most common method for analysing Biodiversity :- 

Where :-

• D = Diversity (0 = No diversity to 1 = Infinite diversity).

• N = Total number of organisms of all species. 

• n = Total number of organisms of a particular species. 

• Σ = "Sum of" all values. 

Note - Students do not need to learn formula, they will be provided in questions where needed. 

Quadrat Case Study : Garden lawn

A Quadrat was used to study the biodiversity of a graden lawn, with the following data being gathered :-

Simpson's Diversity Index for the Garden Lawn : 

Transect (Line or belt) Sampling

Quadrats are also used more systematically, using a Transect. A transect involves using a quadrat (if belt type) or rope (if line type) along a straight line across an area and is used to investigate how species change across an area. Abiotic factors (such as moisture level or temperature) influence the species that are present in a particular location.

Representing a Transect Graphically

The results of a Transect can be represented visually using a type of graph known as a Kite diagram. Kite diagrams show both distribution (location) and abundance (number) of organisms across the transect.

The distribution of a species along a transect can be shown by its position along a central horizontal line in each section of a kite diagram, with each section representing a different species.

The abundance of a species can be shown by the width of the 'kite' around the central horizontal line.

Net Sampling

Quadrats and Transects work well for stationary organisms such as plants or barnacles, but they do not work for moving organisms. In order to sample moving organisms, Net sampling can be used. In net sampling, a net is swept through an area being sampled to collect small organisms, allowing their abundance to be recorded. 

Nets can be used in streams to sample invertbrates living in the sediment through a method known as 'Kick Sampling' :-

Trent Biotic Index

For aquatic (water-based) sampling, the Trent Biotic Index is the most common method for analysing Biodiversity. It assesses the water quality of rivers and streams, based on the presence and diversity of aquatic macroinvertebrates. 

The table below is used with the Trent Biotic Index to assess levels of water pollution : 

To determine the level of pollution, the following method should be used : 

1. Look at row A (Stonefly larvae). If none of the sampled invertebrates fit this group, move on to row B. 

2. Repeat down the table until a row is reached which contains sampled invertebrates. 

3. Select the appropriate column based on the total number of species sampled. 

4. The intersection of the row and column gives the index value.  

Trent Biotic Index Case Study : River Sample

The river Esk outisde Edinburgh was sampled through kick sampling and the following data was recorded : 

Traps (Pitfall, Camera + Mammal) 

Traps are another method that can be used to sample a population. By temporarily trapping or imaging organisms, their presence in an area can be determined. 

A Pitfall Trap is a simple device used to catch usually ground-dwelling invertebrates, such as beetles. A Pitfall Trap consists of a container buried so that its top is level with the surface of the ground, with a covering to prevent birds from eating the trapped invertebrates, as well as preventing rainwater from filling the trap. Once counted, the invertebrates are released back into the environment.

Camera Traps are composed of a digital camera connected to an infrared sensor to detect animals moving past the camera. When an animal moves past the sensor it causes the camera to trigger, recording an image or video to a memory card for later retrieval. 

Camera traps provide data on species location, population sizes and how species are interacting. They also allow observation of species without direct human interaction.

Mammal Traps are humane traps used to temporarily capture small mammals (such as mice) in order to calculate their abundance in the ecosystem. The traps have a one way entrance; once the mammal enters it cannot escape. Once counted, the mammals are again released unharmed back into the environment. 

Capture - Mark - Recapture & The Lincoln Index

A variation on Trapping can be the Capture - Mark - Release method. In this method, the organism is captured in some way, they are counted, and then marked or tagged in some way that is harmless to them. They are then released back into the environment.

At a later date, traps are again used, and the number of marked and unmarked organisms is counted. An estimate of the total population can then be estimated using the following equation, known as the Lincoln Index:-

Note - Students do not need to learn formula, they will be provided in questions where needed. 

Lincoln Index Case Study : Pine Martin

Using a series of Mammal traps, 17 Pine Martin living in a forest were collected, marked with tags and released. When the traps were checked again a day later, 3 marked and 12 unmarked Pine Martin were counted, then released. 

Measuring Abiotic Factors

Organisms all have requirements for life that mean they are suited to their habitats, this is known as adaptations. For example, an Arctic Seal has a thick layer of blubber to keep it warm in the cold Arctic water. If you took that same animal to a tropical ocean, it would quickly overheat and die. 

These environmental factors that affect an organism's ability to live in an area are known as 'Abiotic Factors'.

Investigating Abiotic Factors : Choice Chamber

The impact of abiotic factors on an organism can be investigated using a device such as a "Choice Chamber". This is a circular set of chambers, each with a different set of conditions : 

The conditions within the choice chamber are controlled by : 

Using water and drying agents to control the moisture level.

Covering sections to control the light level.

When organisms such as woodlice, are introduced into the choice chamber, the organisms will tend to move to the areas which have the most favourable conditions for them :  

Investigating Abiotic Factors : Soil Moisture (Crucible & Oven Method)

In the field, a soil moisture probe can be used to measure the soil's moisture level, giving a fairly reliable result. A more accurate way of measuring the soil's moisture, known as the 'Crucible & Oven' method, requires samples to be collected and then returned to the lab.  

The collected samples are weighed whilst wet, heated in an oven overnight to dry, and then re-weighed. The difference between the two measurements will give the mass of water in the original sample. 

For example :  

Investigating Abiotic Factors : Biological Oxygen Demand

The Biological Oxygen Demand is a measure of the dissolved oxygen that microorganisms consume while decomposing organic matter in a water sample. When the water has a low biological oxygen demand, it is an indicator of good water quality : 

Limitations of Sampling Techniques

In Science, it is of huge importance that the results gained are 'reliable'. 

Sampling techniques provide good information about the frequency and distribution of organisms in an area, but there will always be limitations within the procedures which can cause errors in the overall analysis, making the data less reliable. 

Limitations can include :- 

Identifying organisms incorrectly when recording 

The 'sample size' is too small 

'Random sampling' is not actually random 

Errors in equipment set-up or use

Identification Errors

The data gathered in all field work is only valid if all organisms are correctly identified. In some cases, this is easy to do (for example, a daisy and a buttercup look very different), but it is not always so easy. Similar species will look very similar, and can cause huge errors in data if organisms are misidentified. 

Misidentifying organisms can also come with health risks. Every year in Scotland, people are poisoned after eating wild Fungi they thought were safe to eat, because they thought they were a different species. This is why it is not recommended to eat any Fungi found in the wild, unless it has been checked by an expert (and these can also make mistakes!).  

The example below shows how easy it is to make mistakes when identifying Fungi:-

A way to reduce identification errors is to use paired-statement keys to aid identification. Paired-statement keys use paired questions with branching pathways to identify an organism:-

Averages : Mean, Median & Mode

In sampling, the 'average' for the data gathered is usually sought, but the particular type of average will depend on the requirements of the investigation. 

There are three types of average used : 

• Mean - The sum of all the values in a data set divided by the total number of values in that set.

• Median - The middle value in a data set that has been arranged in numerical order. 

• Mode - The value that appears most frequently in a data set.

Standard Deviation & Interquartile Range

The size of a sample taken should be as large as is practically possible to do, as the larger the sample size, the more accurate the results will be, giving a better representation of the sampled population. The larger the population size, the smaller the 'margin of error' in the data will be. The smaller the margin of error, the more likely the data reflects the full population. 

The graph below shows how increasing the 'sample size' affects the 'margin of error':-

Taking many repeat measurements or having a large sample size will also make it easier to spot an anomalous result. Anomalous results (a result that doesn’t fit in with the pattern of the other results) can be easily spotted in the data and discarded, leading to a more accurate calculation of the mean. 

The 'spread' of the data above can be analysed mathematically by calutating the following : 

• Standard Deviation 

• Interquartile range

What is meant by 'Random' ? 

In all of the sampling discussed so far, there has been the assumption that the small samples taken were representative of the area or populations as a whole. This is only true if the samples taken were 'random'. 

There are three types of random sampling used within Higher Environmental Science :- 

• Simple Random Sampling 

• Systematic Random Sampling 

• Stratified Random Sampling

Reliability and Validity of Results

Any results gathered through sampling are meaningless unless they are both 'Reliable' and 'Valid' : 

Reliability -  The consistency and dependability of a scientific measurement, experiment, or finding. This means that if you repeat a measurement, you will get roughly the same result each time. For example, large sample sizes or ensuring effective random sampling will improve reliability. 

Validity - A measure of how accurate, well-founded, and reflective of the real-world phenomenon being investigated a set of results is. The more robust and well-planned an investigation is, the more valid the data gathered will be. For example, using a 'paired statement key' will make an investigation more valid by reducing the risk of misidentification. 

"Do No Harm" :  Invasive and Non-Invasive Sampling

When sampling living organisms, it is very important to take into account ethical concerns regarding welfare. There are legal requirements in Scotland to govern how much we can interfere with wild animals. For example, under Scottish law, it is illegal to intentionally take, damage, or destroy a wild bird's nest while it is in use or being built, according to the Wildlife and Countryside Act 1981. 

Beyond legal concerns, there are scientific concerns regarding how we sample organisms, as how we interact with an animal can greatly affect its behaviour : 

Reliability, Validity & Harm Case Study : Glen Affric 

Glen Affric is home to a variety of iconic Scottish animals, such as red deer, red squirrels, otters, grouse and pine marten. 

In a monitoring exercise, environmental scientists were trying to determine whether the construction of a new access road with wildlife corridor tunnels affected the genetic diversity of otters in the area by sampling 23 sites spread evenly across the glen. The scientists used a range of sampling techniques; sampling DNA obtained from hair traps, camera traps at each sample location and mammal traps allowing physical examination before being fitted with GPS tracking collars. 

The table shows the scientists’ assessment of the effectiveness of each technique for meeting the objectives of their research : 

Q1 : Hair samples were collected from every wildlife corridor along the motorway. Explain why the results of this study could be considered reliable. 

Samples were collected from 23 wildlife crossings; therefore, a representative sample has been collected. 

OR 

Every individual in the population had an equal chance of being sampled. 

Q2. Explain why the use of three techniques would increase the validity of the study.

None of the techniques alone could be used to meet all the objectives of the research and, as some of the techniques can be used to meet the same research objective, the findings from the use of one technique could be used to back up the findings of another.

Q3. The scientists determined that hair sampling was a better technique for identifying individual otters, rather than physical examination and fitting the otters with a GPS tracking collar. Suggest a reason why hair sampling was determined to be the better technique.

The animal does not need to be captured/no harm comes to the animal/it’s non-invasive.