1. Marine iguanas (Amblyrhynchus cristatus) are found on the Galapagos islands of Genovesa and Santa Fe. Marine iguanas are unique among lizards in that they feed on algae in the intertidal zone. Between feeding they lie in the sun to warm themselves. Male iguanas establish territories on the rocks where females lie. Males provide no parental care of offspring while females guard the nest for a few days. Females mate once and use up 20% of their body mass in reproduction, while males try to mate more than once and do not use up much of their body mass.
The graphs below show the lengths of males and females on the two different islands, sample size (N) is indicated for each graph.
[Source: Freeman and Herron, Evolutionary Analysis, (2000), 2nd edition, page 296]
2. Comparison of mammalian brain areas has often focused on the differences in absolute size. However, in an experiment, scientists compared the sizes of 11 different brain areas relative to the total brain size for various primate species. A cerebrotype was then defined for each species, which reflected the relative sizes of different brain areas. The diagram below shows the clustering of cerebrotypes within primates.
[Source: Damon A Clark et al., Nature (2001), 411, pages 189–193]
The relationship among hominoids was constructed using the cerebrotype data and is shown below. The evolutionary trees derived from DNA sequence and bone and tooth structure (morphology) are also shown.
3. Basking sharks (Cetorhinus maximus) filter feed on zooplankton (small floating marine animals) in temperate coastal seas. Marine biologists recorded the swimming paths taken by two basking sharks about 8 km off the coast of Plymouth (UK). At the same time the densities of zooplankton (in g m–3) were recorded within 3 m of the swimming path of the sharks.
[Source: D W Sims and V A Quayla (1998) Nature 393, pages 460–464]
4. Copepods are very small crustaceans and an important component of plankton in the Arctic sea ice. The distribution of copepods, which feed on microalgae, can be related to the food and predators. The biomass of microalgae was measured and the concentration of chlorophyll a was calculated. The graphs below show how the concentration of chlorophyll a and copepods change with depth.
[Source: Martin Fortier, et. al., Visual predators and the diel vertical migration of copepods under Arctic sea ice during the midnight sun” (2001), vol. 23, issue 11, pp. 1263–1278, by permission of Oxford University Press]