(^) Oxygen consumption per unit weight, measured by before-and-after Winkler
titrations, decreases with body size. That is true of animals in general, of course.
Hummingbirds have higher metabolism per gram than eagles, and babies have higher
metabolism per gram than parents. For zooplankton the decrease is more pronounced
in the tropics than in high latitudes. In the figure the scatter is fit by regression lines
equivalent to:
(^) or:
(^) That derives (divide by Weight) from Rate = a(Weight)b, an allometric relation
applicable to many biological rate-to-size comparisons. At least for the data as Ikeda
grouped them, b (slope) decreases and a (position) increases with habitat temperature
(boreal ∼8°C, tropical ∼28°C). The latter effect is obvious: warmer conditions drive
most processes faster, including biological rates. However, respiration differences are
not as large between regions as they would be for a single species experiencing such
large temperature changes. That is because species of cold and warm habitats adapt to
produce rates of movement and activity as closely similar as changes in biochemistry
allow. For example, speed capabilities for predator attack and prey escape will be
pushed by selection toward hydrodynamic limits not set by temperature. Change in
slopes between regions is not altogether understood. For some reason, log[respiration]
compared among species in the tropics and subtropics is almost proportional to body
surface area (b ∼ 2/3), while in higher latitudes it is more affected by body mass (b
closer to three-quarters). The change in slopes represents an interaction of size with
ff
(ff)
#1