In terrestrial environments, predator body size is largely correlated with prey body size. The opposite is found for many predators in the marine environment – baleen whales in particular comprise some of the world’s largest mammals and yet they feed on something far smaller (plankton). The leopard seal is unusual in that it feeds both at the top and at the bottom of the food chain, consuming large prey, such as penguins and other seals, and small prey, such as krill, an abundant basal component of the Antarctic food web. While leopard seals are well known as raptorial predators with a ‘grip and tear’ feeding styles, a large portion of their diet (krill) is too small to be eaten in this way. For this, they use filter feeding to separate the krill from seawater.
Seabirds are well adapted to acquire their prey. Those that feed on bivalves close to the surface have short, strong bills to break into shells and access molluscan meat, and those that feed on bivalves buried deeper in the sand have much longer, slender bills to access their prey. The association between bill morphology and the prey type of different bird species is a frequently cited example of niche differentiation, where animals living in close proximity have evolved distinct feeding strategies which prevent them from being in direct competition with each other (known as resource partitioning).
There’s nothing quite like seeing something in the field. I came to this realisation about half way through my Masters course. When I started, I was a fully-fledged Geoscientist and taking on biological knowledge would have been an immense challenge if it hadn’t been for the engaging, rapid-fire seminars given by Dr Rob Hughes. He was responsible for the series of lectures dubbed the ‘rampage through the phyla’ – a crash course in invertebrate taxonomy, morphology and ecology. Many a lecture was spent sketching the characteristics of a particular family with the urgency of a Pictionary player under pressure, which is how this came about:
In a great many species, females exhibit preferences for larger males – including that world-dominating species Homo sapiens (though a recent PLoS ONE study reveals the effect is only modest in actual couples). Certainly in the marine environment, choices such as this correspond to greater fitness in a species, with larger individuals being more fertile than smaller ones. Fishing can disrupt mating systems by altering population size structure – that is, causing a shift to smaller individuals. This is a particular problem when populations are fragmented (due to patchy habitats), as there are already limits on partner choice. Lobsters populations are often fragmented and with this in mind, Drs Denice Robertson and Mark Butler have investigated the size preferences of the spotted spiny lobster (Panulirus guttatus).
Colima, Mexico. The goal: unearthing the secrets of Vulcán de Fuego or the “Volcano of Fire”. Fuego erupts roughly every two hours. Nothing major, just an outburst of billowing steam clouds from the summit, generally lasting no more than 10 minutes. These outbursts release pressure in the magma chamber below, and by letting off steam; this active volcano poses little threat to the village of La Añilera, below. However, any change from this typical cycle could hint at an upcoming eruption, so researchers at the University of Colima keep a watchful eye on Fuego’s activity. Today (ahem… some time ago, but we can pretend!), I am playing the part of one such watchful eye.