(a)The species have been carried by marine trade on the hulls of ships and in bilge and ballast water and the movements tend to be between developed areas, reflecting trade patterns. Some areas are not involved; these tend to have less trade.
There may be some specific knowledge of individual species from Figure 3 which should be credited, as should other species not shown on Figure 3 (rats).
The major disruption is to food chains, as the alien species out-compete existing species reducing their numbers or even causing extinction. This can be directly through predation, or indirectly by occupying ecological niches. There is also the possibility that disease might be spread by new species, and in some cases damage to the physical make up of ecosystems (erosion). Biodiversity can be severely reduced, and in the worst cases ecosystems collapse.

Level 2 5-7 Structure is satisfactory. Does explain the pattern with some clarity. Some understanding of impact on ecosystems and uses some geographical terminology, but incomplete; makes reference to map. Explanations are clear, but there are areas of less clarity. Lacks full range. There are some grammar, punctuation and spelling errors.

(b) Indicative content
The question requires both scales of threat to be covered, which could be accomplished using the same or different examples from within the named global ecosystem.
In terms of global threats, the likely focus will be on climate change as an overarching threat to forests, coral and others. This threat may be occurring now, or projected to occur. Resource demand may also be considered globally.
At a local level threats are likely to be associated with development and exploitation of resources (perhaps directly, or indirectly e.g. oil), possibly pollution. Tourism is a possibility, in terms of coral or forest destruction, plus urbanisation and other economic development.
Expect marine or terrestrial examples of global ecosystems (biomes).

Level 4 13-15 Carefully structured. Genuine evaluation of a range of threats; provides an overview of balance of threats for named areas; detailed real world exemplification. Judgements present. Descriptive language is well employed and precise. Explanations are always clear. Geographical terminology is used with accuracy. Grammar, punctuation and spelling errors are very rare.