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
1 (self-contained unit containing) community of / all / different, organisms / populations / species, and their interactions ;
2 (with the) biotic and abiotic, environment / factors OR
with each other and with the physical environment ;
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.
role / function, of a species within its, ecosystem / habitat ;
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.
(interrupted belt) transect ;
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.
were assessed:
1 abundance / density / (\%) frequency / \% cover, of (selected) species ;
not assessed:
2 number / range, of (different), ecosystems / habitats ;
3 genetic, variation / diversity (within each species) ;
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.
To calculate the genetic variation that exists within a species, scientists:
- obtain DNA sequences from many individuals of one species
- count the number of nucleotides that differ when the sequences of two individuals are compared
- repeat this with different pairs of individuals.
This allows scientists to calculate the mean number of differences at every nucleotide position along the sequence (mean number of nucleotide differences per site).
1 number of / range of (different), ecosystems / habitats ;
2 number of species and their relative abundance ;
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
random sampling using frame quadrats ;
plant biodiversity at each site
Simpson's index of diversity ;