Features

What links different pollinating insects in your garden or sea otters and kelp?

In a recent paper in Royal Society B Becky Morris of Oxford University's Department of Zoology explored how species interactions create networks in which apparently unconnected organisms can affect one another.

I asked Becky about how these networks work and what the possible implications are for how we attempt to conserve biodiversity around the world...

OxSciBlog: How are species organised in networks?
Becky Morris: Species don’t exist in isolation; they are each linked to one or more other species, with which they interact in a variety of different ways, for example as predators or pollinators.

Think of them as being like web sites (the species) arranged on the World Wide Web (the network). For example, all the insects that pollinate flowers in your garden, along with the flowers that they pollinate, could be considered as a relatively discrete network (although they would also interact with species outside this network).

OSB: Why is understanding such networks important?
BM: Because species are organised in networks, any perturbation to one species is likely to have a knock-on effect on many other species in the network, including those with which it interacts only indirectly. Indirect interactions occur when one species affects a second species through one or more intermediate species. Through such indirect interactions, species that are not closely linked can affect each other, something that you would not predict without considering network structure.

A good example of this is in Pacific kelp forests, where sea otters feed on sea urchins. In areas where sea otters have been hunted to extinction, there has been a huge increase in their prey, sea urchins, which has resulted in the urchins overgrazing and decimating kelp forests. The sea otters have indirectly affected the kelp, via the intermediate sea urchins.

OSB: How might it change our approach to conserving biodiversity?
BM: Rather than focusing on conserving species it might be better to focus on conserving networks of species and their functions. In practice this would be extremely challenging. It is really only possible to ensure that the species that are involved in the networks are present; it is not possible to make them interact.

This has has been demonstrated in a recent study in restored heathlands in Dorset, where individual species of plants, bumble bee pollinators and their natural enemies were successfully restored, but the interactions between the bumble bees and certain natural enemies were not reestablished, so the network structure was not restored to how it was in ancient heathland sites.

However, a network approach can be used to evaluate the impacts of practices such as habitat management and biological control, and these practices indirectly affect biodiversity. A network approach will lead to much greater insight than if only species were monitored, but as yet we have no way of actually focusing our conservation efforts on the interactions between species, rather than the species themselves.

OSB: What impact could human activity have on these networks?
BM: Human activities such as deforestation, habitat fragmentation or climate change all have the potential to alter or disrupt network structure, which in turn will affect their susceptibility to species loss, and the functioning of ecosystems.

A recent study led by Jason Tylianakis from Canterbury University in New Zealand revealed changes in network structure for insect communities in coastal Ecuador, along a gradient of habitat modification from the original forest habitat, through coffee agroforest, to the most modified pasture and rice fields. Surprisingly species richness did not change along this gradient of habitat disturbance, so if we looked only for changes in species richness we would not see any effect.

OSB: What future research is needed in this area?
BM: More experiments and theoretical studies are needed, taking into account the variability of the real world. We still don’t understand exactly how networks respond to perturbations, and whether there are critical thresholds at which the loss of species leads to the loss of network structure and functioning (and whether they can be restored). We need to be able to make general predictions, rather than have a case-by-case understanding.

Dr Rebecca Morris is a Royal Society University Research Fellow based at Oxford University's Department of Zoology.

With Halloween almost upon us we thought we should give you a scare of the eight-legged variety.

So I asked George McGavin, of the Oxford University Museum of Natural History, about scary spider encounters and why arachnids deserve gasps of wonder along with our yelps of fear...

OxSciBlog: What has been your favourite encounter with a spider?
George McGavin: My favourite encounter has got to be when I found the goliath bird-eating tarantula (Theraphosa blondi) when filming Lost Land of the Jaguar in Guyana. We went out after dark to scour the forest close to base camp - after several hours we had not found anything and I was beginning to think that we'd never find one when Bruds, one of the rangers, radioed to say he had found a likely burrow.

Sure enough the burrow was occupied by a large female which I was able to coax out using a blade of grass as a lure. Once in the open I blocked the hole with my machete. The spider was the size of a soup plate and although equipped with half inch long fangs, their main defence is to flick tiny harpoon-like hairs in the face of any attacker. This she did with great enthusiasm and the air was soon filled with her abdominal hairs. They got in my face, eyes and throat but I was not going to be deterred.

When she had calmed down I gently picked her up to show to the camera. She was a real star and even leapt off my hand towards the cameraman - a great performance!

OSB: In evolutionary terms how successful are spiders?
GMcG: Arachnids appeared on Earth around 420 million years ago. Today there are about 80,000 species worldwide. They are a very old group and include things like mites, ticks, scorpions, whip-spiders, harvestmen and pseudoscorpions. The true spiders have mastered the use of silk for prey capture, transport, protection and other uses.

OSB: How important are spiders to preserving ecosystems?
GMcG: As terrestrial carnivores arachnids they have a huge impact on populations of insects and other small invertebrates. A hectare of grassland may be home to several million spiders and other arachnids. One species lives in water in a specially constructed silk diving bell and can prey on small fish fry. Recently the first herbivorous spider has been discovered.

OSB: Why do you think many people have a fear of spiders?
GMcG: In the UK 7 million people are arachnophobic to some degree. While it is true that there are a dozen or so species of spiders whose fangs are strong enough to break human skin they will not do you any harm and allergic reactions to spider bites are very rare.

In Australia, however, where there are several dangerous species, people seem a bit more relaxed about their eight-legged friends. In the middle ages in Europe spiders were associated with diseases and death and I wonder if this might be might origin of our phobia.

OSB: What do scientists still need to find out about spiders?
GMcG: While the arachnids are not as diverse as the insects there are still many more species waiting to be discovered. We actually know very little about the lives of most spider species.

 Dr George McGavin is an Honorary Research Associate at the Oxford University Museum of Natural History. 

Tiny flashes of blue light from beneath the icy South Pole could help scientists uncover the origins of cosmic rays and neutrinos.

These flashes occur when neutrinos created by cosmic rays strike nuclei in the ice, releasing energetic muons which travel through the ice faster even than light can -  producing a burst of Cherenkov radiation. This is detected by IceCube, a 'telescope' made up of thousands of optical sensors buried up to 2.5km deep in the Antarctic icecap. This location is ideal because under the huge pressure at such depths the ice is free of air bubbles and very clear.

Subir Sarkar of Oxford University's Department of Physics leads the British involvement in IceCube, he told The Telegraph's Richard Gray: 'Cosmic rays were discovered 100 years ago, but we still have no idea where they come from. At first glance, IceCube seems like a crazy experiment. How can you study the sky when you bury your detectors a mile beneath the ice? But it gives us a new way of tracing their paths back to their source.'

'The real excitement is that neutrinos and cosmic rays will reveal an entirely new way of looking at the universe and allow us to see into places where we haven't been able to before.'

'Currently we have no way of peering into black holes through the dust and gas that surrounds them, so if high energy neutrinos are being emitted from their fringes, then we can 'see' into places we haven't been able to before.'

IceCube isn't due to be completed until 2011, when all the optical sensors will have been installed, but as early as 2006 its detectors began to pick up the flashes of neutrino collisions. It's already identified an area of the sky near the constellation of Vela as a prolific source of cosmic rays.

Being able to spot these very rare neutrino collisions could help us understand the nature of the dark matter thought to make up around 23% of our Universe.

Normally we think of metals in our water supply as a bad thing, but when it comes to trace amounts of metals welling-up from the ocean’s depths we should count ourselves lucky that they appear.

That's because metals such as iron and zinc are essential to all kinds of marine life – they act rather like a 'fuel' that powers ocean ecosystems. On 17 October an Oxford University-led expedition will set sail for the South Atlantic to study these ‘micronutrient’ metals.

'Because they are present in seawater at such low concentrations they are difficult to measure but with this new expedition we hope to revolutionise our understanding of the metal 'micronutrient' cycle and gain insights into the past, present and future of Earth's climate,' explains Gideon Henderson of Oxford University’s Department of Earth Sciences and the Oxford Martin School, who is leading the UK-GEOTRACES consortium.

Gideon will lead a team of 24 scientists from 10 UK institutes aboard the Royal Research Ship Discovery, one of NERC’s research vessels, collecting samples and carrying out experiments on the 39-day cruise from Cape Town to Montevideo.

The RRS Discovery will head to the South Atlantic where the ocean is particularly rich in life, but where the sources of micronutrients are a mystery. By collecting samples, and making a wide range of measurements both on board and back in the lab, the research team hopes to learn how the metals enter and leave the ocean, and how their abundance in seawater influences marine biology.

Much of our understanding of past climate comes from measurements of marine sediments but understanding how climate information is reflected in the chemistry of the sediments is essential if we are to interpret this evidence correctly.

Understanding the cycle is also vital if we are to assess whether proposed geo-engineering schemes, such as 'seeding' the oceans with iron to increase their carbon uptake, might work.

'Changes in marine ecosystems also have a wider impact: these ecosystems are vital for food production, biodiversity, international development, tourism, and pollution management,' Gideon tells me.

'Any changes in the cycling of micronutrients in the South Atlantic will have an impact not just on the local area but also on the natural resources, economies and standard of living of countries around the world.'

UPDATE: Read regular updates of the mission's progress on the UK-GEOTRACES blog.

Tumours seem to pacify our immune system by tapping into our bodies’ codes, but we may be able to use this trick against them in our bid to hunt them down.

Melanomas are not only one of the most aggressive types of human tumours but the cancerous cells are able to survive and proliferate despite the body’s best efforts to destroy them. Professor Vincenzo Cerundolo, Director of the MRC Human Immunology Unit at the University of Oxford, has been trying to establish how melanomas survive these attacks.

Our bodies are continuously fighting off infections and invading cells. We have many methods of defence at our disposal as part of our immune system - a huge, highly organised army complete with different types of troops and manoeuvres.

The ranks include a particularly potent type of cell called a neutrophil. Neutrophils are packed full of powerful enzymes that can destroy cells at the same time as recruiting reinforcements to the area (inflammation). But, as in any battle, there are always fears over friendly fire so the immune system can quickly issue messenger proteins that revert the troops to being passive so they don’t damage the body’s own cells.

The problem is that, as with any code used in war, the enemy can crack it. Vincenzo’s team recently discovered that melanomas have done just that as they also produce the messenger protein that signals inflammation to stop.

The protein concerned is called serum amyloid A (SAA) and it switches neutrophils from being aggressive to being anti-inflammatory. In other words, the melanomas seem to have evolved a way to manipulate the body’s own safety mechanisms so that they aren’t destroyed.

Unfortunately for melanomas though, producing anti-inflammatory neutrophils isn’t the protein’s only effect. The latest work from Vincenzo’s group, published in Nature Immunology, shows that SAA also affects another type of immune cell called an invariant natural killer T cell (iNKT) where it has exactly the opposite effect, jumpstarting the immune response  by activating antibody-producing cells  (B lymphocytes) and recruiting more cells capable of destroying tumours and virus infected cells (Killer T lymphocytes).

Vincenzo explains that 'SAA is used in the body to fine-tune the immune system, keeping the body alert to attack but stopping it from doing any unintended damage. The question of how melanomas can beat the immune system's defences has been asked for a really long time, and melanomas have many tricks up their sleeves, but we think their use of this protein is a really important one. But finding out that SAA also interacts with these iNKT cells was a really unexpected result and it means there’s a possible way of restoring the anti-tumour immune response.'

In healthy people the number of neutrophil cells is already an order of magnitude above iNKT cells, but in cancer patients there are even fewer iNKT cells to attack the tumours. Vincenzo says, 'it’s very early days but there are drugs that can promote activation of iNKT cells which we might be able to use to get patients’ immune systems to fight back.'

'Our bodies are set on the slightly cautious side as we don’t want our immune systems to damage the healthy parts of our body, but if we know what we’re doing we could activate the immune system in the places and at the times that we need it. SAA is secreted during inflammation from any acute or chronic problem such as influenza or arthritis. If we can manipulate iNKT cells sufficiently it could be a very exciting prospect indeed, not just for cancer but for many other inflammatory diseases.'