I ran out of space last week, so I'll finish up today. To do a quick recap, last time I laid out the process of scientific publication and why most scientific results that are published in reputable journals can be trusted. Sometimes mistakes are made and bad data makes it through the review process, but the vast majority of the time, it doesn't happen. It is to no one's advantage to publish false findings. I made this point to try to help people understand that scientific findings that are published in good journals, particularly if there are multiple articles that support the same findings, are almost certainly accurate and correct. Anyone who tells you different is trying to sell you something or manipulate you into believing something that isn't so.
The other part of last week's column was about two ecological findings that have been reported in multiple different studies in multiple journals. One was the drastic reduction in populations of amphibians in North America over the past 20-30 years, and the other was about the massive decrease in Chinook salmon that are making it back to their spawning grounds, leading to a situation where the salmon population might reach a point of no return within the next 20 years. While there are multiple factors contributing to both of these issues, what they have in common is that they are largely man-made. More on that later. Today, we will finish up with three other ecological situations that should be of great concern to everyone, for lots of different reasons.
First, we'll talk about honeybees. Honeybees are the primary pollinators of many food crops, worth up to $200 billion a year. Feral, or "free-living" honeybees do much of that work, but there are also bees that are kept commercially to be transported to different places to be released to pollinate crops. The almond growers in California, for instance, are very highly dependent on "renting" bees to pollinate the almond groves each year. There has been a problem with honeybee colonies that has been studied since at least the 1990's. Many colonies of both wild and commercial honeybees were dying off for unknown reasons. This was alarming for a number of reasons, including the economic impact on crops, honey production and just regular pollination of flowers, trees and other plants. It was first noticed in the US, then in Europe and has since spread to Asia and Africa. Overall, the honeybee population has remained fairly stable over the decades since this phenomenon, now called "Colony Collapse Disorder," of CCD, was found. The reason for this is that beekeepers are trying to establish new colonies faster than the old ones are dying out. It's a dangerous race.
There have been a number of factors identified which are most likely contributing to CCD. Parasites, tiny mites, have been found in some dead colonies, but not all. Infections by microorganisms is common, but not universal. Chemicals, such as pesticides and fungicides have been found in many cases, but usually not at levels that would be lethal to the bees. Changes in food sources as droughts and heat stress due to climate change impact the normal plants in an ecosystem has also been cited as a contributing factor in some cases. No single definitive cause for CCD has been found, which makes finding a solution difficult.
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The current hypothesis for a cause for CCD is that it is usually a combination of factors that destroys the colony. Each factor, such as pesticide contamination, may not be lethal by itself, but exposure to chemicals could then leave the bees unable to also deal with a second stressor, like an infection. Similarly, a colony that would normally survive parasites, might be weakened enough by food stress to die off. This combination of factors is concerning from a scientific perspective, because when, for instance, a chemical is tested and found to be non-lethal to bees, and approved for use, it might not kill them outright in the wild, but it might leave them vulnerable to other factors that lead to death for the bees. This sort of interplay among factors means that our testing practices may not be adequate to examine the complexities of the actual environment. In any event, this is an indicator that the natural system that is responsible for a significant amount of our food production (not to mention economic activity) is fragile and threatened by both known and unknown factors.
The second issue is about monarch butterflies. Monarchs aren't as important for pollination as honeybees, although they do play a role. They are also part of the food chain for birds and other animals. So, not only are they part of an interrelated biosystem, they are also pretty, and that's not nothing in a world that needs all the pretty it can get. Monarchs are also part of one of nature's greatest migrations. North American monarchs spend their summer in the northern tier states and Canada. They then migrate to southern California and Mexico in the winter, as distance of over 3000 miles. In some places in Mexico, the monarch colonies can cover many acres of forest, numbering in the millions. However, those numbers are decreasing. The population of monarchs, like many insects fluctuates quite a bit from year to year, but the swings have gotten bigger in the past 20 years, or so, and the total numbers, overall, keep going down. In 2018, the population of monarchs in southern California and Mexico was down over 80% from historic norms.
There are a couple of factors that contribute to this decline. One is that the monarchs have a very specific dietary requirement. Monarch caterpillars only eat milkweed, and the species depends on finding milkweed as it migrates from its northern range to the south. The development of herbicide-resistant crops has allowed farmers to control weeds and increase crop yields, but it has also drastically reduced the amount of milkweed available to insects. Coupled to this loss of habitat is the increasing temperature in the butterflies northern breeding ground. As the temperature rises, the butterflies have to move further north, which then extends the distance of the winter migration, causing even more stress on the population.
The third issue is something more recent. It was very much unexpected and very alarming. A study published in the journal "Science" last month reported that the bird population of North America had dropped by over 3 billion (that's with a "B") birds, almost 30% of the entire avian population, since 1970. No one was expecting anything like that amount of loss. The study which was spread across the continent and is very well-documented, demonstrates how huge changes can often go unnoticed, particularly when the change is occurring in a large pool, like the bird population. It's easier to see when bald eagle populations are tanking, as they did in the 1960's and 70's, due to DDT use, because eagles are predators at the top of their food chain and there aren't that many of them, relatively speaking. Changes in small populations are easy to see.
The causes of this drastic die-off have not been fully explained, although habitat loss and pesticides certainly play significant roles. The impact of habitat loss is obvious, and it can be due to both direct and indirect human activity. As native grasslands, wetlands and forest habitat are altered, particularly in areas that are most important for bird breeding and migration, it impacts the ability of the populations to reproduce. Environmental toxins, such as pesticides and herbicides, accumulate in birds as they eat insects and plants, thus weakening the birds and making them less resistant to disease and less able to tolerate long migrations and changing weather. Three billion fewer birds in 50 years.
The point to all these stories is that we are impacting the world we live on, often in ways we don't even realize. None of the animal species or families I've mentioned are in immediate danger of extinction, but they are in danger. The populations don't have to completely die out before extinction becomes inevitable. Once populations fall below a certain level to allow for genetic stability, they can't recover.
These animals are giving us a warning. They live in the small biosphere we do. They are part of the same ecosystems of which we are a part. They are just more sensitive to the changes that are happening than we are. The amphibians are telling us that toxins are building up in the water. The fish are telling us that we have way overestimated the capacity of our waters to absorb whatever we care to put into them. The butterflies are telling us that our need to been ever more productive in growing food to feed an ever-expanding human population is not sustainable. The bees are telling us that the things we are doing are connected to each other and that one thing can combine with the next to produce unexpected consequences. The birds are telling us that the more we do to change the land and water to accommodate more people, the less room there is for everything else. They are all telling us that the climate is changing and the impacts are already being seen.
I don't want to ever experience "The Silent Spring", foretold by Rachel Carson in 1962. We must be stewards of our planet, not just users and consumers. We have done a lot, particularly since the 70's to lessen our impact on the environment, but even with all that, our animals are telling us that it hasn't been enough. We can't even see some of the changes that are happening.
Michael J. Howard, Ph.D., is the Founder and CEO of ARCH Community Health Coalition, Inc.