Practise biodiversity by distinguishing ecosystem, species and genetic measures, selecting sampling methods for organisms, and interpreting population, correlation and diversity data.
The natural ecosystem on Hawadax Island in Alaska was disrupted in the 1780s when brown rats, Rattus norvegicus, swam to the island from a sinking ship and then rapidly increased their population size.
The rats occupied a new niche on the island as predators. The rats ate the eggs and chicks of birds such as the black oystercatcher, Haematopus bachmani, and the glaucous-winged gull, Larus glaucescens. These birds make nests, lay eggs and rear their chicks on the beaches of the island.
Define the terms ecosystem and niche.
ecosystem
niche
Conservation ecologists carried out a project to try to restore the natural ecosystem of Hawadax Island. In 2008, they removed all rats from the island.
Before removing the rats, the ecologists measured the abundance of birds, invertebrates and seaweeds on eight of the island's beaches. Seaweeds are large algae that grow attached to rocks on the beach. The ecologists repeated these measurements in 2013 and in 2019, so that they could calculate the percentage change in abundance from 2008.
To measure the abundance of invertebrates and seaweeds, the ecologists used this method:
- They laid 30 m tapes from high-tide mark to low-tide mark on the beach.
- They placed quadrats at 5 metre intervals next to the tapes.
- They took a photograph of each quadrat.
- They analysed the photographs to calculate the percentage cover of seaweeds and the percentage cover of invertebrates such as mussels and sea snails.
State the name of the sampling technique used.
Biodiversity can be assessed at a number of different levels.
Identify the levels of biodiversity:
- that were assessed by this sampling technique
- that were not assessed by this sampling technique.
Biodiversity can be assessed at three different levels. One of these is the genetic variation within each species.
Outline two other levels at which biodiversity can be measured.
The Venus fly trap, Dionaea muscipula, is a carnivorous plant. It has traps which catch insects.
Each trap consists of a pair of modified leaves joined by a midrib of hinge cells. The modified leaves have touch-sensitive hairs. If two hairs are touched within 20 seconds, or the same hair is touched twice in rapid succession, the trap closes.
D. muscipula grows naturally in a small region in eastern USA. Fires that destroy much of the vegetation occur in this region. Three sites in this region where there had been fires were identified and investigated.
- Site 1 had experienced a fire 2 years before.
- Site 2 had experienced a fire 10 years before.
- Site 3 had experienced a fire 30 years before.
Preliminary observations suggested that over the course of time following a fire, the biodiversity of plants had increased. However, the abundance of Venus fly trap plants had decreased and so had the light intensity available to them. There was also a decrease in the nitrogen that the plants absorbed from insects as a proportion of all the nitrogen they obtained from their environment.
Name an ecological or statistical method to measure:
the abundance of D. muscipula at each site
plant biodiversity at each site
The Venus fly trap, Dionaea muscipula, is a carnivorous plant. It has traps which catch insects.
Each trap consists of a pair of modified leaves joined by a midrib of hinge cells. The modified leaves have touch-sensitive hairs. If two hairs are touched within 20 seconds, or the same hair is touched twice in rapid succession, the trap closes.
D. muscipula grows naturally in a small region in eastern USA. Fires that destroy much of the vegetation occur in this region. Three sites in this region where there had been fires were identified and investigated.
- Site 1 had experienced a fire 2 years before.
- Site 2 had experienced a fire 10 years before.
- Site 3 had experienced a fire 30 years before.
Preliminary observations suggested that over the course of time following a fire, the biodiversity of plants had increased. However, the abundance of Venus fly trap plants had decreased and so had the light intensity available to them. There was also a decrease in the nitrogen that the plants absorbed from insects as a proportion of all the nitrogen they obtained from their environment.
Name an ecological or statistical method to measure:
the abundance of D. muscipula at each site
The soft rush plant, Juncus effusus, grows in many habitats in Northern Europe. An investigation was carried out to assess whether there was a relationship between the height of soft rush plants and the altitude at which they grow on exposed hillsides.
The mean height of 10 soft rush plants was calculated at each of eight different altitudes.
The results are shown in Table 8.1.
Table 8.1
The statistical test, Spearman's rank correlation , was applied to find out if there was a relationship between the altitude and the mean height of the soft rush plants.
Use your value for to evaluate the relationship between the altitude and the mean height of the soft rush plants.
Bears are several species of mammal in the family Ursidae.
Climate change and loss of habitats due to human activity have reduced the size of some bear populations in recent years.
The scientists calculated a D value of 0.833 for the undisturbed population.
Explain what is shown by the difference in the D values between the two populations of bear.