Question 1
Discuss how global warming may affect the distribution and diversity of ecosystems.
Expression of ideas
The sub-headings below are for guidance only. Credit should be given for the Marking points whether the student identifies them under these titles or not.
Global Warming element:
climate change/biomes shift;
Distribution:
biomes move towards higher latitudes / altitudes;
Credit a detailed example
Diversity:
if the shift is too rapid some species will not be able to survive, decreasing diversity;
if the species are on islands or mountains they may run out of space to migrate to;
keystone species/critical to ecosystem, whole ecosystems may be lost/damaged;
changes to the precipitation/temperature/humidity may make an area more or less conducive to the existing ecosystems;
For example, desert areas may receive more rainfall so allowing a more diverse ecosystem;
For example, Sub-Saharan areas receive less rainfall leading to desertification / (southward) expansion of Sahara desert increased fires in tropical rain forests (due to higher temperatures or increased aridity) would lead to loss of species / reduce niches;
altered rainfall patterns might reduce habitat diversity;
Global Warming element:
melting ice caps/permafrost;
Distribution:
exposed areas after melting in high latitudes and/or altitudes;
Diversity:
the newly exposed areas might support new tundra ecosystems, potentially increasing diversity;
if ecosystems space in the tundra is reduced then diversity decreases;
flooding of coastal area ecosystems will reduce ecosystem diversity;
positive feedback loops might occur with the release of methane/clathrates accelerating further global warming/ climate change, stressing ecosystems even more;
Global Warming element:
Changes to the oceans/aquatic areas (higher water temperatures/change in El Nino frequency and intensity);
Distribution:
areas closer to the surface/shallow depth ecosystems are more exposed to the changes;
Diversity:
higher temperatures are likely to bleach/destroy some coral ecosystems; ...and accelerate ocean acidification, damaging plankton/base of marine ecosystems;
ocean circulation may alter allowing some areas to become more diverse;
a possible change of deep sea currents may benefit some areas that would receive more nutrients, thus increase species diversity;
a possible northward movement of Gulf Stream may benefit Iceland and Greenland (ameliorate temperature);
Global Warming element: thermal expansion of sea/ sea level rise;
Distribution of biomes:
increased erosion of coast/ alteration of continental shelf landscape may alter the extent of littoral/shallow coastal zone;
flooding of coastal ecosystem may destroy them, e.g., mangroves; ...but at the same time create new littoral/tidal ecosystems;
Diversity:
reduce intertidal habitat diversity as some species won't tolerate the shift of tide lines (low \& high);
creation of new tidal fronts may bring more nutrients thus increase aquatic species diversity;
Marking guidance:
Award [7 max] for marking points above, and [1 max] for a clear conclusion that is justified by points raised.
Note to examiners: An isolated statement/opinion e.g. "global warming will alter distribution / diversity of ecosystems" should not be considered as a valid conclusion. A valid conclusion may, however, be stated within the body of the response rather than at the end, and may involve some balanced decision:
e.g. effect of global warming would be higher in Polar ecosystems as temperature increase is higher there, so low latitude ecosystems may be only partly affected;
[1 max]
Award [2max] for part (c) if response just identifies global warming elements with no reference to effect of global warming on either distribution or diversity.
Award [5 Max] if the answer addresses only negatives or only positives of distribution and diversity changes