Loss of pollinators and extent of overfishing – our impacts on the world are large and getting worse

Posted by on April 10, 2013
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I’ve discovered some interesting recent reports dealing with two aspects of the global environmental crisis – the impacts of global biodiversity loss, and the extent of global overfishing, or perhaps, the impacts of our foolishness and our greed.  We seem to have a foolish disregard for the well-being of species not seen as immediately useful to us, and our efforts to catch fish reveal insatiable greed seemingly untempered by awareness of the need for sustainability.

In writing Our Dying Planet, I spent some time explaining the risks we faced if biodiversity loss continued at the present pace, and I used the role of pollinators as one way of making this case.  Almost 90% of flowering plant species rely on insects to pollinate their flowers and in the absence of such insects these plants would likely fail to reproduce.  I also mentioned a Costa Rican study that had shown the economic value of rainforest due to the enhanced pollination by forest insects of coffee crops on nearby trees.  At the time, there was no solid evidence of the risk to pollination due to loss of insects, although there was considerable concern over the loss of many native bee species, and the growing incidence of ‘colony collapse disorder’ threatens domesticated honey bees.  Two articles published in Science on 29th March 2013 add substantially to our understanding of how pollinators are declining and what this means for pollination.

A broad array of agricultural plants, including cotton, buckwheat, clover, strawberries, coffee, mango, grapefruit and cucumber, are pollinated by insects, and farmers routinely rent hives full of honey bees from commercial bee keepers to sit at the sides of their fields to ensure good rates of pollination.  Many people might suppose that the use of rented hives could completely replace the pollinating activities of wild insects, allowing our agricultural production to continue unimpeded even if wild pollinators were to disappear completely.  While natural plant systems might suffer, our agriculture would not need to rely on nature to pollinate our crops.  The article by Laura Burkle and colleagues from Washington University, St. Louis MO, Montana State University, Bozeman, and University of Illinois, Champaign IL demonstrates convincingly that there has indeed been a dramatic loss of pollinator species, and consequent profound simplification of the network of plant-pollinator interactions at a site in Illinois that has been studied over 120 years.  The article by Lucas Garibaldi of Universidad Nacional de Rio Negro, Argentina, and a global group of 49 co-authors from institutions in six continents looks more specifically at pollination effectiveness and demonstrates some disturbing facts about just how well those domesticated honey bees do the job.  I’ve linked to the abstracts — both articles are hidden from view without a subscription.

In the late 1800s, Charles Robertson made collections and detailed observations of flower visitation by pollinating insects in natural habitats near Carlinville, Illinois.  Since that time this location has experienced substantial habitat change – most natural habitats have become agricultural fields, and mean temperatures have risen 2oC.  In 2009-10, Burkle and colleagues revisited those sites and collected data on 29 species of forbs (non-grass herbaceous plants) and their 109 recorded pollinator species.  Claytonia J Kelly michiganflora-netThey paid special attention to Claytonia virginica, the Eastern (or Virginia) Spring-beauty (figure © J. Kelly at Michiganflora.net), an early spring flowering plant common throughout this region, and patterns of pollinator visits to it.  For this part of the work, they had access to data and specimens collected at the same location in 1971.

Burkle Science F1.largeTheir results showed a profound loss of pollinator species during the 120 years and a consequent simplification of the network of pollinator-plant interactions.  Only 24% of the 532 pollinator species-plant species interactions recorded by Robertson were observed by the Burkle team.  About half of these losses were due to disappearance (local extinction) of 55 of the 109 species of pollinator recorded by Robertson.  Many of the remaining insect species were observed to visit a greater number of plant species than Robertson had reported, so the overall loss in plant-pollinator interactions was only 43%.  Nevertheless, this means that the matrix of interactions has been greatly simplified during the 120 years.  Their rather complicated diagram (right) shows plant species on the left and insects on the right.  Lost interactions are drawn in red, interactions that persisted in black, and new interactions not observed by Robertson in blue.  Thickness of the lines shows the importance (number of occurrences) of each interaction.

More interesting than the simplification, perhaps, is the evidence they gained on turning attention to Claytonia.  There was no substantive reduction in number of species visiting Claytonia flowers between Robertson’s study and 1971, but this number had dropped by half between 1971 and 2010.  Also, the number of pollinator visits per flower had also fallen precipitously – from 0.59 insects per minute in 1971 to 0.14 insects per minute in 2010.  Further, when they zeroed in on 6 common species of wild bee (genus Andrena) and identified pollen grains on the bodies of specimens collected from Claytonia flowers, they were able to show that these visitors were three times less faithful to Claytonia in 2010 than they had been in the late 1800s.  (That is, pollen of Claytonia represented a smaller proportion of all pollen grains adhering to the bodies of insects collected on Claytonia.)  Reduced fidelity reduces the chance of successful pollination, because the insect may not bring pollen of the right species with it.

The study by Garibaldi and colleagues is larger, and perhaps even more significant.  They recorded visits to flowers by pollinators in 600 fields of 42 different crop plants on six continents.  They contrasted visits by the honey bee (usually domesticated) and by wild pollinators in terms of amount of pollen delivered and success of fruit set, and were able to show that while honey bees brought lots of pollen to flowers,

Garibaldi Science F2B.largeThe effect of visitations by wild insects or honey bees on extent of fruit set for each crop species.  Figure © Garibaldi et al Science 2013.

their success at pollinating, as measured by fruit set, was substantially lower than was that of wild pollinators.  Specifically, while fruit set increased significantly with the rate of visitations by wild insects across all crops examined, fruit set only increased significantly with visitations by honey bees in 14% of crop species.  Taken with the evidence from Illinois of long-term decline in the availability of insect pollinators, this study tells us that it would be foolish to rely on honey bee propagation and distribution to provide pollination services to our crop plants, and that steps to prevent the further loss of insect species should be undertaken.

Also appearing last week, posted on line by the journal Fish and Fisheries, is an article by Daniel Pauly and 19 colleagues from around the world.  It concerns the apparently substantial underreporting of fishery catch by China’s global fishing fleet.  It’s an example of persistent detective work by a group of fishery scientists who began with a simple observation: the size and capability of China’s ‘distant water’ fishing fleet made its reporting to FAO (UN Food and Agriculture Organization) from waters beyond the South China Sea and northwest Pacific of an annual catch of about 368,000 tonnes of fish suspiciously small.   In fact, even Xiaobing Liu, China’s Director of the Division of International Cooperation, Bureau of Fisheries, has reported an annual catch of 1.15 million tonnes, and a similar number is included in information provided by China to FAO, but not in the statistical database of catches.  The detective work, which involved making reasonable assumptions about catch per vessel for particular types of vessel and then matching these to records of vessel activity in different countries has yielded an estimate of an annual catch of 4.6 million tonnes per year, comprised of ~3.1 million tonnes from African waters, ~1 million tonnes from Asian waters (excluding those close to China), 198,000 tonnes from Oceania, 182,000 tonnes from South American waters, and 48,000 tonnes from Antarctic waters.  China’s ‘distant water’ fleet of about 3,400 vessels operates in all regions of the world except the Arctic, the coasts of North America, the Caribbean and European waters.  China claims to have just 1600 vessels.

Pauly Chinese Fishing Nature Pew Charitable TrustsExtent of Chinese under-reporting of catch.  Figure © Nature, and Pew Charitable Trusts

What should we make of this report (which is open to view, not protected)?  First, as Pauly and colleagues take pains to point out, China is definitely not alone in under-reporting its catch to FAO, and under-reporting does not mean the catch was necessarily obtained illegally.  Second, the detective approach necessarily resulted in rather imprecise estimates that might turn out to be high – it will be interesting to watch how this study is received by the fishery science community.  On the other hand, it is wildly improbable that the real total catch is only 368,000 tonnes, and when large numbers of fish are being taken, but not reported, that can seriously frustrate efforts by managers to keep fishing sustainable.  Pauly and colleagues note that virtually none of China’s agreements with other countries granting access to fish in their waters are publicly available, so it is impossible to know whether the ships are operating legally or not.  Given that most global fisheries appear to be overexploited, and that this problem has been getting worse since the mid-1980s, the extent of underreporting that has been revealed here raises serious questions regarding our ability to rein in overfishing and move back towards sustainable catches. Think of this next time you chomp down on all-you-can-eat seafood at a restaurant near you.

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