Hartley Nature Center Programs
Book Reviews: How to save the natural world with native plants
Win-Win Ecology: How the Earth's Species Can Survive in the Midst of Human Enterprise, by Michael L. Rosenzweig,
Oxford University Press, 2003
Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens, by Douglas W. Tallamy, Timber Press, 2007
Birdscaping in the Midwest: A Guide to Gardening with Native Plants to Attract Birds, by Mariette Nowak, Flying Fish Graphics, 2007
Reviewed by Tom Jordan (tjordan@d.umn.edu), July 2008
Biodiversity at home. Not just out there in the woods and wilderness. Here too. In my yard and your yard. Where you and I can grow it most easily. Where we can enjoy it most often.
It’s necessary. There is no way to get around the species-area law, the observed fact that the number of species on a piece of land with suitable habitat is limited by the area of that land. For example, the number of different species of bats on a Caribbean island depends on the area of the island. More area means more species. The same is true for the number of bird species in different tropical Pacific archipelagos, the number of bird species in different areas of California chaparral, or the number of species of fruit-eating birds and mammals in the tropical forests of different continents. It is largely the same whenever numbers of species are counted on comparable pieces of land. [There are differences. The number of species is proportional to a power of the area. The power varies between about 1 and 1/10 for different cases. If the power is 1, the number of species is proportional to the area; an area 9 times bigger has 9 times more species. If the power is 1/2, the number of species is proportional to the square root of the area; an area 9 times bigger has 3 times more species.]
Decreasing area means decreasing numbers of species. In the United States, and even in the world as a whole, our use of the land has left about 5 to 10 percent of the original natural habitat. Therefore, Tallamy says, “When extinction adjusts the number of species to the land area that remains for the plants, mammals, reptiles, birds, and invertebrates … we will have lost 95 percent of the species. … This is not speculation. It is a prediction backed by decades of research on species-area relationships.” [The power in the species-area law is about 1 when the pieces of land are continents, so a 95 percent decrease in numbers of species is a good estimate of the end result of a 95 percent decrease in the habitat area of our continent.]
We can prevent this. Extinctions take time. We have time to act. Lots of species here now are doomed if habitat area continues to be as limited as it is now, but we can change that. “The predictions of mass extinction are based,” Tallamy says, “on the assumption that [most] plants and animals cannot coexist with humans in the same place at the same time. Nonsense! … most species could live quite nicely with humans … if we would just design our living spaces to accommodate them … create living spaces that are … functioning … ecosystems with high species diversity.” Rosenzweig calls this “reconciliation ecology.” He says “We can learn how to reconcile our own use of the land with that of many other species. Maybe even most of them.” He gives encouraging examples.
Rosenzweig lays out a scientific foundation that Tallamy uses. Rosenzweig’s book gives a good account of the species-area law. There are boldly clear graphs of species-area relations for a variety of data sets, including those I mentioned at the start. Rozenzweig explains how species extinction, creation, and immigration shape the species-area law [and why the power in it is different for different cases]. He then describes how these processes work when habitat area is decreased, uses the species-area law in two stages to predict how numbers of species will decrease in time, and finds agreement with two sets of data on observed extinctions.
Rosenzweig developed this broadly aimed book after his more scholarly book “Species Diversity in Space and Time” (Cambridge University Press, 1995) of work built on the classic ”The Theory of Island Biogeography” by Robert H. MacArthur and Edward O. Wilson (Princeton University Press, 1967). Rosenzweig, a professor of ecology and evolutionary biology at the University of Arizona, was a student of MacArthur. The species-area law, the MacArthur-Wilson collaboration, and Wilson’s incredible experiments in the Florida Keys, are described in Wilson’s autobiographical book “Naturalist” (Island Press, 1994; and Warner books).
So, picture your yard teeming with life. Birds. Butterflies. Bugs. We need bugs. Only plants are more basic. Plants get energy from photosynthesis. Insect herbivores play a big part in the first step of moving that energy up the food chain. Tallamy says that “Worldwide, 37 percent of animal species are herbivorous insects. These species are … very good at converting plant tissue to … insect tissue … and … providing food - in the form of themselves - for other species. In fact, a large percentage of the world’s fauna depends entirely on insects to access the energy stored in plants. … About 96 percent … of the terrestrial bird species in North America … rely on insects and other arthropods (typically, the spiders that eat insects) to feed their young.” Indeed, Nowak says, “Songbirds are particularly active as insect predators during nesting when young birds need … insect protein for their growth. Birds, in fact, seem to time their nesting to coincide with plentiful supplies of insects.” Bird feeders can not replace what nature can provide. Nowak reports that a study in Wisconsin found that even in winter “chickadees that visited feeders obtained only about 21% of their food from feeders.”
To counter aversion to insects in the garden, Tallamy asks “How is it that a … woodlot teeming with … insects still has plenty of healthy plants with beautiful foliage? [Because it] is a collection of plants and animals - producers and consumers - that are more or less in balance. Yes, there are insect herbivores eating the plants … but keeping these … in check are dozens of species of insect predators, parasites and diseases. These, in turn are eaten daily by the birds, amphibians, and small mammals. … In a balanced community, with rare exceptions, … if one species … does start to run rampant, it is soon brought back into equilibrium by the other members.”
“Our … animosity toward insects is understandable,” Tallamy says, “but seriously misplaced. Of the 9 million or so insect species on earth … a mere 1 percent interact with humans in negative ways. The other 99 percent … pollinate plants, return … nutrients … in dead pants and animals to the soil, keep populations of insect herbivores in check, aerate and enrich the soil, and … provide food either directly or indirectly for most other animals.” And, Tallamy says, “you may … find pleasure in the exquisite beauty … of insects… . Creating habitats specifically for particular insect species can be its own reward and will connect you to a fascinating part of nature.”
We can relax and let nature work for us. Redirect our efforts. Eliminate pollution and climate change caused by power lawn machinery. Cut our use of water and fertilizer. Eliminate herbicides and pesticides. Stop killing things that would increase biodiversity. We can be filled with joy by the richness of life around us. We can see that, in comparison, an expanse of perfect lawn is artificial, empty, and sterile.
“A sterile garden,” Tallamy says, “is one teetering on the brink of destruction. It can no longer function as a dynamic community. … Its checks and balances are gone. [Its] continued existence depends entirely on the gardener alone. … The self-sustaining balance we seek … is only achieved through complexity.” We want redundancy in the predators that can check unbalanced growth, substitutes for any predators that fail. To make that secure, we need redundancy in the hosts that support the predators. So, “to control insect herbivores, [we] must maintain populations of insect herbivores.” We need enough diversity to have that redundancy.
Particular species of butterflies need particular species of plants. Particular species of birds eat particular species of insects, and particular species of insects eat particular species of plants. These connections, species by species, imply that diversity of birds, butterflies, and bugs requires diversity of pants.
Consequences follow more broadly from one simple fact: most native insects do not eat nonnative plants. They “can only eat plants with which they have an evolutionary history.” Tallamy, a professor of entomology and wildlife ecology at the University of Delaware, tells how when he and his wife moved onto ten acres of land and started working to remove nonnative plants, he noticed the “striking pattern” that the nonnative plants “had very little or no leaf damage from insects.” Since this was a fact with consequences “that neither I - nor anyone else, I discovered, after checking the scientific literature - had considered,” Tallamy started collecting data. Some of it is shown in the book: his native plants supported 4 times more insect biomass, 3.2 times more insect species, and 35 times more caterpillar biomass than the nonnative plants. Nowak reports that a study in Wisconsin “found that the native plants contained the highest numbers of insects and other arthropods, while the extremely invasive Common and Glossy Buckthorns had the lowest numbers.” UMD entomologist Tim Craig and his students have data, yet to be published, that show similar patterns.
Where is the food? In what they contribute to the ecosystem, nonnative plants can be more like plastic ornaments than like native plants. Tallamy describes reasons and gives examples.
Nowak brings Tallamy’s science home to birders and Midwest gardeners. She describes a variety of ways that native plants help birds and birds help plants. “Each spring, migrating warblers arrive just in time to feast on the emerging leaf-eating caterpillars, thus helping keep insects under control until the leaves build up their defenses. Such complex interrelationships between birds and native plants have been perfected over thousands of years of coevolution.” Birds disperse plant seeds. They eat the fruits and seeds of nonnative as well as native plants, but the timing may be better for them with the natives. “Over 70% of the fruits of bird-distributed plants ripen in fall, perfectly timed for peak migration. … Plants even accommodate the migrating schedules of birds, ripening first in the North, later in the South. For example, in New England, most tree and shrub fruits ripen in August and September, which coincides with the migration of thrushes and other birds. In the Carolinas, the fruits ripen a month later. … This … is … remarkable considering plants in the South generally flower earlier in the spring, sometimes by as much as six weeks.”
Nowak’s book is about relations of plants and birds, with bugs playing secondary roles. Tallamy’s is about relations of plants and bugs, with birds playing secondary roles. Relations of birds and bugs, with plants playing secondary roles, are discussed in “The Birder’s Bug Book” by Gilbert Waldbauer (Harvard University Press, 1998). The whole ecosystem matters. Every part counts.
The delight is in the details. They are illustrated with a wealth of color photographs in both the Tallamy and Nowak books. All three books are rich in examples. Nowak’s is the most detailed about how to landscape a yard.
Native plants. We need simple rules: organic, local, renewable, native. What makes a plant native? Tallamy gives a functional definition: if members of the native ecosystem interact with it like they would with a native plant, then it is native; if they do not, it is not. Just being around for a few hundred years is not enough.
Biodiversity is what we most want to preserve as human population peaks. The species diversity that remains when/if population stabilizes will be a lasting measure of our stewardship. By working in the right direction and making progress in our own yards, we can build hope that maybe we can save the natural world after all. These books are a good part of the instruction manual.
Be sure to check our Public Programs link to the left for more fun opportunities, and call us at the number below with questions.
724-6735
Click a link:
Our Focus: Natural History, Stewardship, Sustainability.
About Us: HNC staff & farm history
E-Mail us at info@hartleynature.org
Any weird stuff happening here? contact the webtech @ LadyHawlke Design Company arr c2004