Note: This program first aired July 23, 2016.
Ecosystems are like salad bars, you fill your plate with
lots of leafy greens and then sprinkle lesser amounts of more concentrated food
items on top (nuts, olives, bacon bits). Ecosystems have a similar food or
trophic structure, at the bottom are the primary producers, the plants and
other photosynthetic organisms, as you move up at each level there are fewer
and fewer non plant individuals ( herbivores, omnivores and carnivores).
Land plants are the primary producers of terrestrial
ecosystems, doing the work of capturing the sun’s energy on dry ground, they
are the lettuce on the salad bar of the forest. And it turns out there are
bacon bits here in the forest as well, in the form of caterpillars. As
herbivores these organisms are able to transfer the energy that plants capture
from the sun to higher trophic levels in the forest food web. That is what I
learned listening to a talk from University of Delaware entomologist Doug
Tallamy when he came to Maine to speak earlier this summer.
Tallamy’s work looks at the relationship between the primary
producers, insects and the upper trophic levels, mainly birds. And what he has
discovered has profound implications for the way we manage the landscapes
directly under our control. It turns out that if you want birds around,
particularly migratory song birds, you need insects, specifically caterpillars.
These birds migrate thousands of miles to northern North America to breed,
because of the plentiful food sources here.
Caterpillars, which are made up of fat and protein, are very
nutrient dense and make up a huge proportion of that food for many of these
birds. Tallamy recalled watching a pair of birds feeding their young,
calculating that the nest of young birds were fed hundreds of caterpillars a
day, thousands over the two week period they spent in the nest. And here is
where it gets interesting, because if you want caterpillars around,
caterpillars being the larval stage of lepidoptreans, the butterflies and
moths, you need plants, because caterpillars eat plants.
But not just any plants, caterpillars generally eat specific
plants, plants they have a long evolutionary relationships with. Plants do
everything they can to not be eaten, evolving elaborate chemical warfare
against hungry insects. Insects do everything they can to evolve physiologic
means of evading the plant defenses, in an ever escalating evolutionary game,
the relationship between the eater and the “eat-ee” gets more and more
specific. We have all heard about the monarch butterfly and its host plant common
milkweed, but many lepidopterans have this level of specificity with their
target food source. Others are less specific and play the field, having
relationships with plants in more than one genus. And plants are not
monogamous, as the “prey species” in this relationship, they have many
different insects trying to eat them, and can play host to tens to hundreds of
different kinds of caterpillars.
What Tallamy and his lab have quantified is the number of
different lepidopteran species (in the form of the caterpillars—which are the
stage in which these insects do the majority of their primary production energy
transfer) various genera of plants support. The results are astonishing. In my
area, native tree genera like willow (Salix) and oak (Quercus) can support
between 300 and 350 different types of caterpillars! Other native tree genera support nearly that
many. The corallary to this is that nonnative trees and shrubs, frequently
planted as part of “normal” landscaping, support virtually no caterpillars,
because no native insects have evolved ways to evade these plants’ defenses.
None. Insects are the animal that is responsible for transferring the majority
of primary productivity from plants to the rest of the terrestrial food web.
Birds, reptiles, amphibians, spiders, and rodents all rely on caterpillars as a
food source. So if you don’t have plants that support insects, you don’t have
anything else in the food web either. Biodiversity
is our life support system, and what I learned from Doug Tallamy is that it
starts from the ground up, in an elegant and fundamental relationship between
those that eat and those that are eaten.
References:
Doug Tallamy’s book on native plant landscaping in the
suburban environment: http://www.bringingnaturehome.net/
Download the data from Doug Tallamy’s studies here: http://udel.edu/~dtallamy/host/
One of Doug’s popular science articles (slightly dated) but
with interesting stats: https://www.americanforests.org/magazine/article/backyard-biodiversity/
Our local native
plant advocacy group, Wild Seed Project, has lists of appropriate native plants
(to Maine) for different environmental conditions: http://wildseedproject.net/using-natives-in-the-landscape-a-comprehensive-plant-list/
The native plant finder at the National Wildlife Federation
site: http://www.nwf.org/nativeplants-beta/About
(its a beta version--still a little buggy, no pun intended, for example, when I
searched my zip code some high scoring trees did not appear, but when I
searched them individually they showed up in my zip code…)
Nutritional info on caterpillars: http://healthland.time.com/2013/08/21/why-eating-bugs-is-good-for-you-its-about-the-nutrients/slide/caterpillar/
Want to eat some bugs yourself? Here’s a list of internet
resources: https://edibug.wordpress.com/where-to-get-bugs/
