Why are some leaves red

Q: How does photosynthesis occur in plants that are not obviously green, such as ornamental plum trees with deep purple-colored leaves? [Paul, Santa Cruz]

A: Photosynthesis (which literally means “light” “put together”) is that very elegant chemical process that jump-started life as we know some 4 billion years ago. So to answer your question, we’ll have to do a short chemistry lesson. Basically six molecules of water (H2O) plus six molecules of carbon dioxide (CO2) in the presence of light energy produce one molecule of glucose sugar (C6H12O6) and emit six molecules of oxygen (O2) as a by-product. That sugar molecule drives the living world. Animals eat plants, then breath in oxygen, which is used to metabolize the sugar, releasing the solar energy stored in glucose and giving off carbon dioxide as a by product. That’s life, in a nutshell.

All photosynthesizing plants have a pigment molecule called chlorophyll. This molecule absorbs most of the energy from the violet-blue and reddish-orange part of the light spectrum. It does not absorb green, so that’s reflected back to our eyes and we see the leaf as green. There are also accessory pigments, called carotenoids, that capture energy not absorbed by chlorophyll. There are at least 600 known carotenoids, divided into yellow xanthophylls and red and orange carotenes. They absorb blue light and appear yellow, red, or orange to our eyes. Anthocyanin is another important pigment that’s not directly involved in photosynthesis, but it gives red stems, leaves, flowers or even fruits their color.

Many plants are selected as ornamentals because of their red leaves—Japanese plums, Norway maples, and purple smoke bush, to name just a few. Obviously they manage to survive quite well without green leaves. At low light levels, green leaves are most efficient at photosynthesis. On a sunny day, however, there is essentially no difference between red and green leaves in trapping the sun’s energy. I have noticed the presence of red in the new leaves of many Bay Area plants as well as in numerous tropical species. The red anthocyanins apparently prevent damage to leaves from intense light energy by absorbing ultraviolet light. There is also evidence that unpalatable compounds are often produced along with anthocyanins, which may be the plant’s way of advertising its toxicity to potential herbivores. So red-leaved plants get a little protection from ultraviolet light and send a warning to leaf-eating pests, but they lose a bit of photosynthetic efficiency in dimmer light.

Botanists have been wondering about red versus green leaves for the past 200 years and there is still much research to be done in this arena. So you are in good company, Paul.

Michael Ellis – Ask the Naturalist Column – Bay Nature Magazine
Send your questions to atn@baynature.org.

Swarming Dragonflies

Q: Last October, while hiking on Mount Tamalpais, near Laurel Dell, I saw numerous swarms of dragonflies. Could you tell me more about this phenomenon? Is it seasonal? Or triggered by weather or courtship? [Khiem, San Jose]

A: Those dragonflies were most likely congregating to hunt, catch, and eat abundant insects that were also swarming. This is indirectly weather-related, because dragonflies are active only on warm days. Most need an air temperature of at least 63 degrees to get moving.

Dragonflies and damselflies belong to an ancient insect group called the odonata, some of the earliest flying creatures on our planet. Dragonflies are big, strong fliers. They have very large eyes and hold their wings out straight when resting. Their cousins, damselflies, are smaller and have a weak, fluttery flight. Damselflies have small eyes and rest with their wings held up directly over their thorax.

While driving through the Central Valley near Williams last August, I encountered thousands, maybe millions, of common green darners, our state’s second-largest dragonfly. As far as I could scan through binoculars in every direction for miles and miles, the air was filled with them. These iridescent giants were in constant flight, hunting insects breeding in the standing water and irrigation ditches so prevalent in this fertile agricultural land. On Mount Tamalpais I have seen swarms of common greens but also of the variegated meadowhawk. I suspect the latter may be what you saw. This widespread dragonfly, which grows to about two inches long and varies in color from pink to tan to dull gray, can be active year-round in the Bay Area, even in winter.

The swarming you saw probably had nothing to do with mating. There are over 60 kinds of dragonflies in California and more than 28 in the Bay Area, so mating strategies vary quite a bit among species. In some species, males wait and pounce on females as they fly by, and there is little color difference between males and females. The males of other species, like the western pondhawk, establish territories over a patch of prime real estate (rich with insect prey—freshwater ponds, lakes, streams, rivers, even poorly maintained hot tubs) and chase off rival males and attempt to copulate with every female that comes into their range. These species sometimes show a marked difference between females and males; the males are brilliantly colored with more vibrant facial patterns, which make it easier for them to tell potential mates from rivals.

Two great references are Kathy Biggs’s self-published pocket-size guide Dragonflies of California (Bigg’s Wildlife Pond) and Tim Manolis’s UC Press field guide Dragonflies and Damselflies of California (UC Press).

Santa Rosa-based naturalist Michael Ellis leads nature trips around California and throughout the world with Footloose Forays.

Native Snails

Q: What native land snails live in the Bay Area? Where do the common garden snails come from, and what’s the status of our native snail populations? [Erica, Mountain View]

A: If you are a gardener like me, you eventually come to despise snails with a passion, even if you’re a kind, gentle, loving person. And while you would not dream of actually torturing them, you have few qualms about ending their slimy little mollusk lives.

Our wet and relatively mild Bay Area winters are peak time for land mollusks. The snail that most of us encounter is the European garden snail (Helix aspersa). These animals were brought to California over 100 years ago, allegedly as a food resource. So when you collect them in your garden, you might as well eat them. They are about 15 percent protein, 3 percent fat, and the rest water. Dipping them in garlic butter will greatly improve the flavor and add quite a few calories. But make sure to properly prepare these snails, which must be purged before it’s safe to eat them (search “snail’s pace” at Matt Bites for details).

So much for nonnatives. I remember the first native snail I ever saw in the Bay Area. Hiking in Muir Woods in early winter, I found a lovely specimen. The shell was very dark and not as tall as the common garden snail. The flesh had beautiful, subtle shades of purple. It was Monadenia infumata, or the Monadenia land snail, and simply gorgeous.

The most common native land snails are the shoulderbands in the genus Helminthoglypta. They can be easily confused with garden snails. But instead of the broad, somewhat fuzzy brown pigment of the European snails, these natives have a very distinct single dark band that wraps around the shell at the “shoulder.” There are over 60 species in California, including the Morro shoulderband snail or banded dune snail (Helminthoglypta walkeriana) and the Coast Range shoulder-band snail (Helminthoglypta nickliniana), among others. Mostly our native snails can be found in relatively undisturbed native ecosystems.

Another snail that is commonly overlooked is called Haplotrema minimum, the California lancetooth. This species not only feeds on plant material but also hunts and eats other snails and slugs.

Dr. Barry Roth compiled the “Checklist of the Land Snails and Slugs of California,” available from the Santa Barbara Museum of Natural History, and he is generally considered our local snail and slug expert. He says there is no indication that the introduced European garden snails and other exotic land mollusks are affecting our native snail populations. The introduced species live in areas with significant habitat modification, where the natives are already long gone. Apparently as long as the habitat is intact, the native snails will do fine.

Santa Rosa-based naturalist Michael Ellis leads nature trips around California and throughout the world with Footloose Forays.

Colony Collapse Disorder

Are native bees suffering the same colony collapse disorder as honeybees?
Q: Are native bees suffering the same “colony collapse disorder” as honeybees? [Linda, San Ramon]

A: Colony collapse disorder, or CCD, has gotten a lot of media attention, and with good reason. The western honeybee (Apis mellifera) is native to Europe, Africa, and western Asia and was brought from England to Virginia in 1622. The bees, known to some Indians as “the white man’s fly,” readily escaped and spread on their own to the Great Plains. Their progress west was stopped by the Rocky Mountains, until hives were shipped to California during the Gold Rush.

Honeybees are now a major workhorse (er, make that work-insect) for Big Agribusiness and therefore the rest of us. Crops pollinated by honeybees in the United States are worth over $15 billion a year. Every February bees are trucked or flown in from all over the country and even Australia to pollinate California’s almond trees. So when millions of bees disappear, everyone takes notice, including the National Academy of Sciences and the U.S. Congress.

CCD seems to affect only certain commercial beekeepers, who reported bee die-offs of 30 to 70 percent last year! (Organically kept bees and feral hives do not suffer CCD.) Many causes have been suggested-malnutrition, pathogens, immune problems, mites, genetically modified crops, fungi, pesticides, antibiotics, long-distance transport, and electromagnetic radiation, including from cell phones. The last one got a lot of airtime: Use a cell phone, kill a bee. But there’s little evidence to support that. Some sort of immune system collapse is more likely.

Honeybees aren’t the only game in town, however. Native bees are also significant pollinators of food crops. While they are mostly solitary or form only small colonies, California natives are actually more versatile and effective pollinators than honeybees. Mason bees and bumblebees are active when honeybees are not, such as early in the spring and on cold days, and they are more effective at pollinating tomatoes, cranberries, and potatoes. And flowering plants have evolved for the last 100 million years with their respective insect pollinators, so native bees and native plant life cycles tend to coincide.

There are at least 1,600 native bee species in California, according to our resident expert, UC Berkeley’s Gordon Frankie. He says they are not suffering from CCD, but populations are declining due to habitat loss and pesticide use. Agricultural agencies and organic farmers are beginning to recognize native bees’ value. There are many ways to attract native bees: Creating good nesting sites, planting native flowers, reducing pesticide use, and protecting wild habitat all tend to increase the diversity and number of our native bees.

Michael Ellis – Ask the Naturalist – Bay Nature Magazine

Which Birds Mate for Life

Q: Do any local breeding birds mate for life? Why? [Leo, San Francisco]

A: Some local birds do form long-lasting pair bonds of several different kinds. Ravens and scrub jay pairs hang out together all year, not just at breeding time. Wrentits and resident Canada geese also have long relationships that can last more than ten years.

Most songbirds have the same mate every spring, but this has more to do with site fidelity than with long-term partnership. Males usually arrive early and use songs and displays to define, control, and defend the same territory each year. If a female arrives and finds the same male, courtship ensues, copulation follows, and both tend to the young. But if last year’s male lost his territory, then the new guy will do just fine. So real estate is more important than individuals. But there is a direct correlation between fitness and the ability to secure good territory.

Most of the 12 seabird species that breed in our region mate for life. But it’s fidelity to territory, not to individuals.

Scientists are discovering through DNA analysis that pair bonding does not mean complete faithfulness. There is a lot of cheating going on. The proper term for this is —extra pair copulation,— and both males and females do it. This may increase the genetic diversity and therefore the viability of the offspring. But we are far from understanding the complexities of avian sexual relations.

The evolutionary bottom line is how many thriving offspring you leave behind. There are successful species of birds that mate for life or for a season or for one copulation. Each strategy works for whatever species uses it.

Michael Ellis – Ask the Naturalist – Bay Nature Magazine