It’s hard to keep wild animals out of farms. Birds, mammals and insects all affect crop yields, in positive ways (such as flies pollinating flowers) and negative ones (such as when birds damage fruit).
Agricultural research and management programs often deal with these interactions by focusing on simplistic “good” and “bad” labels: aphids are annoying pests, for example, whereas bees are little angels.
In reality, however, no animal is 100% a “goodie” or “baddie” – their effects on crop production vary with context. Interactions between animals and crops are influenced by seasons, landscapes, management practices, and other animals. They can also be affected by the social, cultural and economic values of the local farming community. The same species can be “good” in one system and “bad” in another.
It sounds complicated, because it is. But this is where ecological research can help. Understanding the interplay between these factors will help ensure that farms can protect wildlife while also providing us with food and other resources.
Good versus bad?
When we reviewed 281 papers that evaluated increases or reductions in crop yields due to wild birds or insects on farms, we found that the binary view of “good” and “bad” animals is still widespread.
Of the studies we looked at, 53% (mostly in the agricultural sciences) focused on identifying and managing the “baddies”, by weighing up costs that animals create for farmers by damaging crops. Another 38% (mostly ecology and conservation studies) calculated the impact of the “goodies”: benefits such as pollination and pest control. Only 9% of the studies we reviewed considered both costs and benefits in a single system.
This shows that most scientific studies are still taking an approach that is too simplistic. Attempting to link increases or reductions in crop yields with a single pest or helper species doesn’t usually tell the whole story. It doesn’t tell us about other factors that influence crop yields, like seasonal changes in animal activity, effects of different management practices, or interactions between different animal species.
Because so many studies have focused on quantifying the effect of one group of animals (such as bees), or focused on effects at one crop development stage (for example, using fruit set as an indicator of pollination efficiency), the overall body of knowledge on how wild animals affect crops has become disjointed and sometimes contradictory.
In a second paper, we suggest a new way to address these complex issues that considers the social and environmental contexts of crop production across the entire growing season. By looking at the interplay between the various positive and negative effects, we can gain a more realistic estimate of how crop yields are affected by wild animals.
Here’s an example. In Australian almond orchards, native birds are often considered pests because they can cause crop losses by pecking at developing fruit. But after harvest has finished, the same birds also remove the decaying “mummy” nuts left on trees. Growers sometimes use paid manual labour to remove these nuts, because they harbour disease and pests that can damage the trees.
A cost-benefit analysis of shows that the positive economic value of the birds cleaning up the mummy nuts outweighs the cost of crop losses from damaged almonds. Averaged across the entire plantation, the presence of the birds is a net positive for farmers. This means that letting birds do their thing could be more cost-effective for growers than deterring the birds and then paying people to remove the mummy nuts. But without this cost-benefit approach, it easy to imagine how farmers would persist in viewing the birds as crop pests and shooing them away.
Very few studies have considered how wild animals create this type of cost-benefit trade-off in farming ecosystems. Yet this approach is central to the study of ecology, and there are obvious parallels between natural and agricultural systems. Both, for instance, have pollination and pest control as key functions.
Farms are ecosystems too. So we need to find a way to maintain sustainable crop production while also protecting biodiversity and ecosystem function. Doing this means moving beyond simplified systems and intensive production.
Productive farms have complex cycles of interactions between crops, wild animals and people. These cycles need to be sustained, not isolated from the system. As with any ecosystem, understanding is the first step towards protection.
Manu Saunders, Post-doctoral Research Fellow (Ecology); Gary Luck, Professor in Ecology and Interdisciplinary Science; Rebecca Peisley, PhD Candidate, Institute for Land, Water and Society, and Romina Rader, Lecturer in Community Ecology, University of New England
An international team of astronomers has discovered that the supermassive black hole at the centre of our galaxy might be the source of mysterious high-energy cosmic rays that bombard the Earth on a daily basis.
The discovery, reported in Nature, brings new answers to one of astronomy’s most longstanding mysteries.
Back to the source
In 1912 Victor Hess found that the Earth was being bombarded by subatomic particles travelling at tremendous speeds that originated from outer space. He called the particles “cosmic rays”. But the origin of these high energy particles has remained a mystery for more than 100 years.
“How cosmic rays are created and accelerated at very high energies is the big question astronomers are trying to understand,” said Associate Professor Gavin Rowell, an astrophysicist from the University of Adelaide, who was involved in the Nature study.
One theory was that cosmic rays are produced during supernova explosions. These create “remnants” that send shock waves throughout the galaxy. This electrically charges particles in space, which are then accelerated to near the speed of light, eventually hitting the Earth.
However, because the particles are mangetically charged, any magnetic field in space will change their direction. That means it’s difficult to determine their origin once they strike our atmosphere.
In this study, the researchers used the High Energy Spectroscopic System (HESS) telescopes in Namibia to look for the very fast flashes of light created when cosmic rays collide with the Earth’s atmosphere.
Using this data, the researchers were able to estimate the direction of the cosmic ray, and found it pointed back towards the centre of our galaxy.
This coincides with the location of what is believed to be a supermassive black hole, with a mass of 4 to 5 million solar masses. The HESS team suggest that the huge gravitational force exerted by the tremendous mass of the black hole was able to accelerate the particles to their incredibly high velocities.
“This result adds a new dimension in cosmic rays, and how the cosmic rays our galaxy is producing could also come from this massive central black hole,” Rowell said.
Professor Geraint Lewis, an astrophysicist at the University of Sydney, emphasised that the study also makes us aware that the universe can do things that far outstrip what we are capable of here on Earth. However, our understanding of cosmic rays is still far from complete.
He mentioned that the biggest question is explaining the precise cause of the particle acceleration.
“It is like a game of Cluedo: they’ve tied down what they think is the site of the murder, but now they are trying to locate the weapon,” he told The Conversation.
What it does tells us is that the cosmos can accelerate particles to velocities that far exceeds what we are capable doing on Earth.
“These particle accelerators in outer space put the Hadron Collider in the shade,” he said.