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HUMAN IMPACTS ON MARINE ECOSYSTEMS – NOT JUST A SIMPLE NUMBERS GAME

It’s well known that removing large numbers of top predators from the ocean impacts on the abundance of their prey, their prey’s prey and the small creatures and vegetation those prey eat: a phenomenon called a ‘trophic cascade’.

However, according to Professor Robert Warner of the University of California Santa Barbara, it’s not just a simple numbers game. By removing the top predators, we are also indirectly affecting the behaviour, reproduction and diet of prey and predator alike, changes that are potentially more disruptive for marine ecosystems than simple predation alone [1]. Professor Warner is in Australia as the 2013 recipient of the prestigious Selby travelling award and is discussing some of these indirect effects at Macquarie University today.

Parrotfish hiding from predators (photo: Peter Vorotnikov)

Parrotfish hiding from predators (photo: Peter Vorotnikov)

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The secret life of social spiders.

Adult D.cancerides and offspring sharing prey

Adult D.cancerides and offspring sharing prey (Agnarsson & Rayor, 2013)

In the Hobbit, young Bilbo Baggins fights to free his terrified companions from the webbed larder of a colony of giant spiders. But spiders that hunt cooperatively only exist in the realm of fantasy, right? Not so, according to renowned spider expert, Linda Rayor of Cornell University, New York. Speaking at Macquarie University today, Rayor explains that social spiders, though rare, are very real.

Only a tiny number of spiders (just 88 out of the 44,000+ known species) display what is termed ‘prolonged sub-social’ behaviour: A maternal-offspring relationship that extends beyond the customary maternal defence of the egg-sac and on to active food provision and protection of the young into adulthood [1]. The relationship may be more tolerant than loving in nature, but in the world of spiders, anything less than cannibalism is remarkable. Continue reading