More Mayslake Fruits

by Carl Strang

Earlier I featured several plants at Mayslake Forest Preserve that produce fruits timed to coincide with the fall migration of berry-eating birds. This mutualistic interaction for the most part benefits the birds, through nutritional provisioning, while the plants get their seeds dispersed. Today I want to feature some outliers to this pattern. Let’s start with Solomon’s plume, also known as false Solomon’s seal.

Solomon's plume fruit b

Like many fall fruits, these advertise themselves to birds with a bright red color. When analyzed, however, the berries proved to be junk food, or perhaps are more accurately described as food mimics (White and Stiles 1985, Ecology 66:303-307). The plants save their energy, investing no nutritional value in these fruits. The ruse works, apparently, by exploiting the naïve instinctive response of first-time autumn migrants, the young of the year. A little different from this is the offering of the European highbush cranberry.

European highbush cranberry fruit b

Another study (Witmer 2001, Ecology 82:3120-3130) showed that the nutritional value of these berries becomes available only when they are consumed along with a significant protein source. I was impressed to learn that, like the waxwings native to the shrub’s European home, our North American cedar waxwings ignore these tempting berries until spring, when cottonwoods or other poplars are flowering. Then the birds consume the berries along with cottonwood catkins, protein in the pollen providing access to the berries’ nutritional value.

Common buckthorn fruit b

These black berries are common buckthorn fruits. They generally are ignored by birds until late winter when, apparently, the better quality foods have been depleted. Then, robins and waxwings consume them, unfortunately dispersing the seeds throughout our woodlands. Buckthorns leaf out early and lose their leaves late, casting a shade so dense that no other plants can grow beneath them. This is why these Eurasian shrubs must be removed at the beginning of woodland restoration projects. A final fruit is of no interest to birds.

Buckeye fruit 2b

Ohio buckeyes in fact are largely ignored by animals generally. This opens the possibility that, like other trees I discussed earlier, buckeyes may have been dispersed by now-extinct mastodons and other large herbivores.

Component Communities: Solomon’s Plume

by Carl Strang

 

Continuing yesterday’s subject, I want to focus on the component community centering around Solomon’s plume, another flowering herbaceous plant of DuPage County woodlands. I prefer the English name fostered by the Morton Arboretum rather than the more widely used “False Solomon’s Seal.” Smilacina racemosa is the poetic sounding scientific name.

 

smilacina-with-sawfly-b

 

This perennial member of the lily family produces its cluster of little white flowers at the tip of its stalk in early summer. The name “plume” refers to this cluster. The flowers develop into speckled berries that ripen in the autumn, just in time to fool the migrant birds (they have practically no food value, and are best thought of as food mimics, but that’s a story for another time).

 

I found several insect consumers of this plant in the 1980’s (deer also feed on it as the stalk sprouts up in spring). The earliest is an uncommon large caterpillar, probably in the Noctuidae family, which consumes flowers and possibly fruits in their early development.

 

caterpillar-on-smilacina-b

 

As the fruits begin to form, a sawfly caterpillar appears and begins to eat them. This common species, larva of a wasp relative rather than a butterfly or moth, often consumes all of a plant’s berries, then works on the leaves.

 

sawfly-larva-solomons-plume-b1

 

Sawflies are notoriously difficult to rear to adulthood, and I have not yet identified the species. Finally, in July, there is an unidentified leaf miner which produces a winding linear mine but did not interact to a measurable degree with the sawfly.

 

The biggest impact on the plant was caused by the sawfly. In 1983, 23% of stalks had fruit at Maple Grove, and 33% at Meacham Grove. Sawflies occurred on 88% and 93% of fruiting stalks, respectively, and removed averages of 41% and 74% of the fruits.

 

Once the leaves have matured they are relatively safe from herbivores, the leaf miner alone able to specialize on that resource. Scientists have found that plants defend their tissues with chemicals that poison or at least interfere with the digestive systems of their potential consumers. Herbaceous plants are more varied in their chemical defenses than are woody plants. This means that their associated insects tend to become specialized in their diet, able to evolve ways to deal with one kind of poison produced by a single plant or group of closely related plants. A result of this is the component community structure I described yesterday, with each kind of plant hosting the few consumers that have solved the puzzle posed by its defenses.

 

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