You’ve seen posters and read bumper stickers. You’ve watched news videos and opened colorful solicitations for money. Cries of “Save the bees!” and “Protect our pollinators!” are ubiquitous, having replaced pleas for pandas, whales, and spotted owls. But wait. How can you save a bee?
The truth is, you can’t. Not really. If you catch an endangered rusty-patched bumble bee and put it on your sun porch with flowers and sugar syrup, you’ve gained nothing. If you snag a monarch butterfly and give it an entire greenhouse full of the finest milkweed, you’ll receive nothing for your efforts except a large invoice.
We simply cannot save individual insects. We can’t even save large aggregations. The one and only thing we can protect is a pollinator’s habitat. If pollinators have the space they need, and that place is filled with their natural foods, building materials, housing choices, and water, then and only then can we begin to save them.
Connectivity is Key
Note that I said, “begin.” That’s because even a perfect environment containing all the desired components must be connected to others like it. Small populations must interact with other populations in order to share genes and maintain diversity.
Populations that are cut off from each other can spiral into oblivion, something the biologists call an extinction vortex. In simplistic terms, the smaller a population becomes, the more it inbreeds, and the more it inbreeds, the faster the gene pool shrinks. As the gene pool shrinks, it offers fewer genetic choices to future generations, meaning the offspring are less likely to have the traits that would allow them to survive unusual circumstances such as pathogens, droughts, or predators.
In one study, researcher Penelope Whitehorn monitored populations of native bumble bees, Bombus muscorum, on nine islands off the coast of Scotland that were isolated from mainland populations.1 She found the island populations to be much more susceptible to a parasite called Crithidia bombi that lives in the bee’s gut. In addition, the inbred populations were much more likely to produce infertile males, which further weakened the breeding population.
Weaknesses such as susceptibility to parasites or infertility are much more likely to show up when a population is small. Although so-called bad genes occur in large populations, too, most bad genes are recessive, so they express themselves only in the homozygous state. That is, an individual must have received the same recessive gene from each parent.
Of course, the genetics of haplodiploid creatures such as bees operate a bit differently. Since males have only one set of chromosomes, a so-called lethal gene would not be passed to progeny through the male. Instead, a male with a lethal gene would simply die. But in fact, most genes that affect the fitness of bees are not lethal. For instance, genes affecting foraging ability or cold tolerance can easily be transferred to female offspring through both parents.
Although double recessives are possible in a large population, they are statistically rare. However, in a small inbreeding population, a bad gene may become quite common, so offspring are much more likely to get a pair of them. This condition, called inbreeding depression, can cause a population to fail quickly. Like water circling a drain, the population gets smaller and weaker until it just disappears.
Habitat fragmentation hastens extinction
Biologists have been studying habitat fragmentation for years, mostly in the form of island biogeography.2 After monitoring island populations, studying their fossil records, and comparing them with similar populations from other islands, a number of principles became clear. Chief among these is large islands will host a greater number of species than small islands, and islands that are close together will have more species than islands farther apart. Area and distance are keys to species richness.
Large islands have lots of resources and many variations of habitat. Think of Australia as a large island, and you can see lots of opportunities for a variety of species to thrive. Habitats are extremely varied and the landmass is so large, the chances of inbreeding are small.
Now think of an island of ten acres in the middle of the Atlantic. Surely, it could support some forms of life, but the opportunities are limited. The number and types of habitat are small, food sources are limited, inbreeding is high, and if something goes terribly wrong — like a hurricane — the whole thing could collapse.
In contrast, let’s put a similar little island a quarter-mile off the Australian coast. The insects and birds living on that island are close enough to interact with populations on the mainland. With occasional cross-breeding with those “foreign” populations, the gene pool is strengthened. Even after a catastrophic event such as a storm, populations can be boosted with input from the mainland.
Slicing and dicing the continent
Back here in North America, we too have a big chunk of land with lots of habitat to choose from and plenty of resources. Islands, in the traditional sense, are rare, and most of the ones we have are close to a large landmass. So what’s the problem?
The problem is simple. We have segmented our continent into millions of small parcels that are disconnected from one another. This division, called habitat fragmentation, produces biological islands. The landscape is still physically connected, but travel between the different pieces is impossible for many species.
In nature, many features can cause a patch of land to be a biological island. Think of mountain ranges, deserts, rivers, and lava flows. All of these things can stop species from moving in or out. But the number of those natural barriers doesn’t hold a candle to all the artificial barriers we have built and the sheer number of biological islands we have created. The impenetrable walls we have built leave wildlife locked into wastelands of limited resources and restricted genetics.
Have you ever seen an aerial photo of New York City’s Central Park? It’s a perfect biological island, a green oasis surrounded by multiple roads and immense skyscrapers, which are further surrounded by expanses of water. Even now, some creatures can get in and out by themselves, including certain birds and insects, but most cannot.
Unfortunately, a habitat fragment doesn’t need to be nearly as spectacular as Central Park. Nearly any park in any city is a fragment, as are most wildlife preserves and conservation areas. At some point, they are bounded by highways, cities, agricultural fields, shopping malls, industrial areas, parking lots, stadiums, and residential developments. To many animals, these are as impenetrable as oceans.
When considering pollinators, remember that honey bees have an extraordinary flight range, which allows them more opportunity than most bees. Many bee species have flight ranges of perhaps 300 yards, which basically means they can’t even cross a modern parking lot. It means that few populations in an average town can connect with each other, which can lead to what the biologists call “local extinction.”
A local extinction starts small. The ball field on the edge of town which used to nestle against a forest is now surrounded by housing developments. The small bees, beetles, and fragrant violets that used to grow there disappeared over time leaving nothing but weeds, mosquitoes, and broken bottles. It doesn’t sound like a big deal until you realize it’s happening not just in one ball field, but in hundreds and thousands of similar areas. Soon, instead of a local extinction, you have entire states and then regions of extinction. The total obliteration of a species happens one individual at a time.
The pesticide question
Many of the special interest groups that defend pollinators spend a lot of time and energy — not to mention money — on trying to restrict insecticide use. Clearly insecticides are problematic and more prudent use of pesticides would likely benefit pollinators. But we must remember that even if we banned every last pesticide, pollinators would still be imperiled by habitat fragmentation alone. What we have here in North America and across the globe is thousands of tiny populations, all suffering from genetic isolation.
It is easy to point to something like insecticides and say, “There it is! There is the problem. Make it go away and everything will be better.” But how do you make habitat fragmentation go away? With a world population rising along with sea levels, we cannot expect that cities and roads, industry and agriculture are going to disappear any time soon. Instead, we need to get creative with the landscapes we have left.
Connecting the dots
The importance of connecting divided populations has not been lost on conservation biologists. In fact, many impressive corridors have been built to accommodate a wide variety of animals. For example, the Trans-Canada Highway has six dedicated overpasses and 38 underpasses that have not only reconnected wildlife populations, but have prevented countless wildlife collisions on the road.
Similarly, 56 miles of U.S. Highway 93 in northwest Montana have 41 wildlife and fish crossings and 39 jump-outs.3 An even more unusual set of structures — 31 underpasses and one bridge — were built in Christmas Island National Park in Australia to accommodate millions of crabs on their annual migration. Equally impressive projects can be found in Singapore, Kenya, and the Netherlands, which carry endangered species as well as common ones.
So if wildlife corridors are vital to bears and badgers, why not for insect pollinators? It’s easy to think that since insects fly, they don’t need help crossing the street. But that is not necessarily so. It turns out that insect pollinators need some legs up as well.
Insects have special needs and unique problems. Take the monarch butterfly, for example. Monarchs need to travel amazing distances to complete their life cycle, and along the way they need to eat and to rest, just like everyone else. Because they need fresh wings to complete the entire migration cycle, they even breed along the way! But cities and towns, highways and airports have replaced their precious milkweed with concrete, pavement, and landscapes sprayed free of “weeds.” The corridors of these creatures need to be lined with milkweed — the larval host plant — if the species is to survive.
In contrast to monarchs and other migrating animals, most insect pollinators don’t fly very far from their natal nest. Since travel is limited, everything they need — including mates — must be within that short flight range. Instead of acting like flyways, insect corridors simply allow connectivity between populations, allowing them to interact with each other. Think of an insect corridor as a bucket brigade of sorts. Each of the individuals remain close to home, but buckets of genetic material get passed along in both directions, providing a constant flow of genetic material in and out of small populations.
Bees can be difficult
Every animal presents a unique set of problems and bees are no exception. For example, the alfalfa fields of the Touchet Valley in eastern Washington are home to the largest population of managed alkali bees anywhere on earth. These native ground-dwelling bees — wearing show-stopping stripes of pearlescent green, orange, blue, and yellow — labor tirelessly to pollinate the seeds that will be shipped worldwide. So when the state decided to widen the local two-lane road into a freeway, the alfalfa growers wanted to know how to protect their 120 acres of nesting bees.
In response, Washington State University ran a four-year study to learn how to help the bees cross the road. In one experiment, they erected tall mesh fences along both sides of the roadway hoping to force the bees to fly up and over the freeway to get to the fields on the other side. Instead, they discovered that alkali bees fly one-to-three feet off the ground. Period. So when the bees came to the mesh, they flew up and over and right back down, just like a pole vaulter. They crossed the road at the one- to three-foot level until they came to the next mesh, and then repeated the maneuver. Needless to say, the mesh was a total fail.
Regardless of similar problems, successful pollinator corridors have been built and more are on the way. Brent Council in north London is in the process of building a seven-mile pollinator corridor that will connect 22 wildflower meadows. The bustling City of Seattle is home to the Columbia Street Pollinator Pathway, a system of gardens that unites two pollinator-friendly landscapes. Nora’s Woods, a small park on one end, is connected to the Seattle University campus on the other. The twenty gardens in between follow strict guidelines for pollinator habitat, but each is maintained by the individual landowner.
Planting trees, whether in rural America or in so-called urban forests, is one of the best things we can do for the planet. Not only can trees produce a huge number of flowers per square foot of planting space, but they provide habitat to countless species beyond pollinators. Trees and shrubs make excellent corridor plants because they can thrive in places limited by pavement and concrete.
Aside from the fact that trees can yield all types of fruit and nuts, they have benefits we sometimes forget. Trees filter the air, absorb pollutants, reduce run-off, provide windbreaks, provide sound and visual screening, lower temperature in their immediate vicinity, and sequester carbon. Furthermore, deciduous trees have the dual benefit of providing shade in the summer and allowing sun exposure in the winter. It’s no wonder honey bees like to live in hollow trunks.
We all can help
While large-scale pollinator initiatives are important, they require cooperation among public entities, businesses, and private landowners. These projects are vitally important, but they can take many years and much money to implement. In the meantime, we should not overlook the good we can do as individuals.
While a small garden or a balcony flowerpot cannot feed many pollinators, it can feed some, and that is the point. Every time we fill a gap in the landscape with a plant that provides a resting place or a minibar to a passing pollinator — or even a trysting place for members of that bucket brigade — we are contributing to the connectivity that is so vital to their survival. No planting is too small to make a difference.
Honey Bee Suite
Notes and References
- Whitehorn P, Tinsley M, Brown M, Darvell B, Goulson D. 2010. Genetic diversity, parasite prevalence and immunity in wild bumblebees. Proceedings. Biological Sciences/The Royal Society. 278. 1195-202. 10.1098/rspb.2010.1550.
- Quammen D. 1996. The Song of the Dodo: Island Biogeography in an Age of Extinctions. New York, NY. Scribner.
- A jump-out is an earthen ramp on the freeway side of a wildlife fence that allows an animal to walk to the top of the fence and jump down to safety.