Ecology. Michael Begon

Ecology - Michael  Begon


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      APPLICATION 2.3 Getting predictions right in the face of climate change

      The effects of temperature on growth, development and size may be of practical rather than simply scientific importance. Increasingly, ecologists are called upon to predict. We may wish to know what the consequences would be, say, of a 2°C rise in temperature resulting from global warming (Section 2.9.2), or to understand the role of temperature in seasonal, interannual and geographic variations in the productivity of, for example, marine ecosystems. We cannot afford to assume exponential relationships with temperature if they are really linear, nor to ignore the effects of changes in organism size on their role in ecological communities. Figure 2.10b shows for 74 fish species how maximum size varies across a steep sea surface temperature gradient in the Mediterranean Sea. If the reason for this pattern is the temperature–size rule (rather than genetic differences between locations) there could be important implications for fishery yields in a warmer climate. Van Rijn et al. (2017) suggest that the most pronounced size reductions will occur in large, active, non‐migratory species that are often the major source of economic revenue, while elevated temperatures may have smaller effects on benthic, less active, and often less valuable, species. To optimise their catch, fishers may have to adapt their fishing strategies.

      2.3.3 Ectotherms and endotherms

Schematic illustration of the avenues of heat exchange between an ectotherm and its environment.

      Source: After Fei et al. (2012).

      Amongst insects there are examples of body temperatures raised by controlled muscular work, as when bumblebees raise their body temperature by shivering their flight muscles. Social insects such as bees and termites may combine to control the temperature of their colonies and regulate them with remarkable thermostatic precision. Even some plants (e.g. Philodendron) use metabolic heat to maintain a relatively constant temperature in their flowers; and, of course, birds and mammals use metabolic heat almost all of the time to maintain an almost perfectly constant body temperature.

      endotherms: temperature regulation – but at a cost

Graphs depict the examples of the thermoneutral zone. (a) Thermostatic heat production by an endotherm is constant in the thermoneutral zone, between b, the lower critical temperature, and c, the upper critical temperature. (b) Mean resting metabolic rate versus ambient temperature in nine Japanese quail, Coturnix japonica.

      Source: (a) After Hainsworth (1981). (b) After Ben‐Hamo et al. (2010).

      ectotherms and endotherms coexist: both strategies ‘work’

      The responses of endotherms and ectotherms to changing temperatures, then, are not so different as they may at first appear to be. Both are at risk of being killed by even short exposures to very low temperatures and by more prolonged exposure to moderately low temperatures. Both have an optimal environmental temperature and upper and lower lethal limits. There are also costs to both when they live at temperatures that are not optimal. For the ectotherm these may be slower growth and reproduction, slow movement, failure to escape predators and a sluggish rate of search for food. But for the endotherm, the maintenance of body temperature costs energy that might have been used to catch more prey, produce and nurture more offspring or escape more predators. There are also costs of insulation (e.g. blubber in whales, fur in mammals) and even costs of changing the insulation between seasons. Temperatures only a few degrees higher than the metabolic optimum are liable to be lethal to endotherms as well as ectotherms (Section 2.3.6).

      It is tempting to think of ectotherms as ‘primitive’ and endotherms as having gained ‘advanced’ control over their environment,


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