Unit 3.2 Life* Flashcards
Explain the centre role of vegetation type in determining the distribution of organisms.
Most species are specific to a particular habitat. This may be due to beneficial environmental conditions, an environmental stress which reduces competition (e.g. wood sorrel and shade), or the presence of a food species. As a result, these species are associated with a specific vegetative type.
Some species, such as the common eel, require a series of habitats through its life cycle.
Other species, such as rat or bracken, are able to thrive in a range of habitats.
Give an example of the chemical and physical properties of a soil influencing floral assemblages.
The Chalk of southern England. Soils are typically shallow, free draining and very alkaline.
Chemical: Chalk milkwort is a calcicole, specialised to alkali soils. It is found only on chalk, and occasionally on limestone.
Physical: Thyme is specialised to dry soils. It thrives equally well on other dry soils.
Describe and explain the relationship between the processes of photosynthesis and respiration.
Photosynthesis, carried out by plants and cyanobacteria:
water + oxygen + sunlight = carbon dioxide + sugars
Respiration, carried out by all living things, relies on sugars produced by photosynthesis, and is the reverse reaction:
carbon dioxide + sugars = water + oxygen
Describe and give examples to illustrate the taxonomic hierarchy of classification.
The taxonomic system arranges similar species into a genus grouping, similar genera into a family grouping, similar families into a single order, and so on through class, phylum and at the highest level kingdom (plantae, animalia, fungi, bacteria, protoctists).
For example: Q. robur and Q. petraea are both in genus Quercus; Quercus grouped with Fagus and Castanea within family Fagaceae. Fagaceae is in the order Fagales, along with Betulaceae (birches, alders and hazelnuts). < order? >
Describe the hierarchy of the British NVC system.
NVC recognises 12 basic vegetative types, each of which are given a code:
- aquatic (A)
- calcicolous grassland (CG)
- calcifugous grassland (U)
- heaths (H)
- maritime cliffs (MC)
- mesotrophic grassland (MG)
- mires (M)
- saltmarshes (SM)
- shingle, strandline, sand-dune (SD)
- swamps and tall-herb fen (S)
- vegetation of open habitats (OV)
- woodland and scrub (W)
Each broad habitat type contains a number of communities. For example, 25 in W, designated W1 to W25. Each of these will refer to a specific community type. For example, W18 is a pine woodland.
Many communities have sub-communities. There are four sub-communities for W18, labelled W18a - W18d.
Interpret a floristic frequency table in terms of community classification.
NVC survey records the abundance (I - V) and frequency (0 - 9).
Comment on the usefulness of community classification compared to monitoring species populations.
NVC survey will not pick up year-on-year changes in a single plant species. If a species population were to decline due to changes in the environment, this environmental change may not be detected for many years. It is therefore not suited to short term monitoring, but should rather be used to monitor longer-term trends of 5-10 years or more.
Define the term ‘habitat’ in two different ways, giving relevant examples if each.
- a range of habitats in which a given species occurs
e. g. snakes-head fritillary occurs in traditionally managed hay meadows on alluvial soils in the floodplains of lowland rivers - distinct unit in the landscape, supporting a distinct community of organisms
e. g. agriculturally improved grassland, chalk grassland
Recall and explain, giving examples, the various ways in which an organism’s environment can be subdivided and classified, with particular reference to an organism’s requirements, the living and non-living components of the environment, and how elements of it act to control the organism’s distribution and abundance.
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Explain the rationale behind the BMWP biotic index and be able to calculate one from sample data, using an appropriate scoring sheet.
Biological Monitoring Working Party.
Species of invertebrate is given a score between 10 and 1: the most pollution sensitive species are given the higher scores. For example, some species of mayflies are extremely sensitive to pollution and score 10, while worms are very tolerant of pollution and so score only 1.
The index is the sum score for all of the species found. A higher score indicates less pollution. The rationale is that, while a greater diversity of species is positive, the presence of some species is more indicative than others, and so their presence must be weighted.
Calculate a Spearman rank coefficient and use it to assess whether there is a significant correlation between the abundance of an organism and an environmental factor.
< handout >
Describe, using examples, how biotic factors can affect an organism’s distribution.
Competition
Predation
Food source
Shelter (e.g. bats in trees)
< bottom-up or top-down >
Define interspecific competition and explain the competitive exclusion principle.
Interspecific competition is the interaction that occurs when the abundance of two or more neighbouring species is limited by the same resource. The effect of competition is to reduce the abundance of both species because they are going to share a finite resource.
The competitive exclusion principle suggests that, if one species is able to outcompete another, then over time it will gain a greater and greater proportion of resources. Eventually, it will gain 100% of resources, and exclude all other species.
List at least three mechanisms by which species are able to coexist and cite a relevant example of each.
- resource variability: for example, a small pocket of soil may be poor in nitrogen, and so favour clover, while the surrounding soil favours grass.
- niche separation: the niche each species exploits may be separated in time or space. For example, wood sorrel completes its life cycle before the tree canopy has closed.
- establishment opportunities: ruderals may not be able to compete, but they can quickly take advantage of disturbance which causes gaps in the vegetation.
- natural enemies: once any species becomes too abundant, it is able to sustain a large population of parasites, diseases and herbivores adapted to feed on it.
- climatic variability: in a particularly cold or wet year, another species, better adapted to these conditions, may be able to compete and establish a place for itself. For example, two grasses compete in the North American prairie; in normal years one is dominant, but the other is more drought-resistant and so flourishes in dry years.
Describe the use of indicator values for ranking the environmental tolerances of plant species.
Ellenberg observed plants, and ranked (1 - 12) them according to their tolerances to seven environmental variables:
- water
- light
- soil pH
- soil nutrient
- temperature
- continentality of climate
- salinity
For example, a plant ranked 1 in water-value is often restricted to places that dry out completely; 7 to damp sites; 12 to submerged plants, permanently or almost constantly under water.
Recall the C-S-R strategy approach to assigning species to functional groups, describe the main characteristics of each of the primary strategies and cite relevant examples.
(C) Competitor species grow rapidly and gain height to outcompete their neighbours. This strategy is resource intensive, and species are late to flower, as their early energy goes exclusively towards growth.
(S) Stress tolerator species are adapted to grow under conditions in which other species struggle. They are slow growing and long-lived; like competitors they will reproduce late.
(R) Ruderal species can not compete, nor can they tolerate stress. They survive by spreading efficiently and, once established, reproducing rapidly and precociously. They are well suited to environments which are frequently disturbed, during which time they survive as seeds.
Comment on the broad changes one may expect in global vegetation in response to global climate change and the basis on which such predictions are made.
Woodward focuses on the physiological tolerance of temperature by the dominant plants of various biomes. Two such variables are the tolerance of cold, and the optimum range of temperatures for leaf growth.
These optimum temperatures for each biome can be compared to predictions of future temperatures. The picture is one of biomes creeping towards higher latitudes: for example, boreal forests will shift northwards, displacing tundra.
Describe in quantitative terms what happens to light energy from the Sun between reaching the Earth’s atmosphere and being incorporated into the tissues of photosynthetic plants as net primary production.
Only 45% of sunlight is within the visible spectrum, as can be used by plants. However, much of this does not fall upon leaves, and some of that which does is reflected from the leaf.
Approximately 10% of the light reaching the surface of the Earth is used by photosynthesis. Some energy is lost during photosynthesis while much is used by the plant during respiration.
In total, only about 1% of sunlight becomes NPP.
