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Monday, September 26, 2016

Ecosystem Engineers and the Web of Life

Goldenrod in bloom
© Beatriz Moisset

Goldenrod bunch gall
© Beatriz Moisset

This time of the year, fields and meadows are usually covered by a plethora goldenrods particularly the tall variety, known as Solidago altissima. Goldenrods nurture a huge variety of small creatures. Some feast on the rich pollen and nectar of their flowers. Others find ways to feed on the not so nutritious leaves and stems. The plants are so abundant and vigorous that they survive quite well the onslaught of all these feeders.

Rhopalomyia solidaginis
(Goldenrod bunch gall midge)
© Beatriz Moisset

Rhopalomyia solidaginis
Larva inside gall
© Beatriz Moisset

The goldenrod bunch gall midge is one of a number of goldenrod feeders that have developed interesting techniques to feed and stay safe from predators at the same time. The larva of this midge injects special substances into the tips of the goldenrod stems. These substances stimulate an unusual vigorous sprouting of the growing stem and leaves. A tight bunch or cluster of leaves with a nutritious, tender center develops. These clusters can be quite numerous in a field of goldenrods. They are easy to spot and they are known by the name of bunch galls. They provide both nourishment and shelter to the insect.

Parasitic wasps, Platygaster sp
© Beatriz Moisset
This story doesn't end there. The midge creates conditions favorable to other small creatures when it builds the bunch gall. Tiny beetles and wasps find a nice place to hide and even raise their families in the bunches of leaves. Curiously, the galls go beyond that. When dead, they become compost and enrich the soil in a larger scale than goldenrod plants free from galls.
Microrhopala vittata (Goldenrod Leaf Miner)
Inside bunch gall
© Beatriz Moisset
Microrhopala vittata (Goldenrod Leaf Miner)
© Beatriz Moisset
This is reminiscent of what beavers do. These animals build dams which provide habitat for fish and frogs and other animals. This have earned them the name of ecosystem engineers. The goldenrod gall midge is also an ecosystem engineer, although in smaller scale. It is surprising how such an insignificant and easily ignored tiny insect can contribute to the web of life.


Further Readings

 

Sunday, June 19, 2016

Bees and Biodiversity


Bombus ternarius, Tricolored bumble bee on mountain mint
 Recently I discussed the idea of allowing dandelions on the lawn to benefit pollinators. I pointed out that such practice only benefits a handful of generalist pollinators, but not the specialists. The latter can be more numerous than the former when they are all counted. They also account for the wide diversity of nature.
Bombus impatiens, Common Eastern Bumble Bee on blanket flower

Andrena cornelli, Azalea andrena on azalea
Let me expand on the concept of biological diversity or, as it is often called by ecologists, biodiversity. There are 4,000 species of bees in North America, from the familiar, big and plump bumble bees to tiny bee species that remain unnoticed to all except to those who study bees. Bear in mind that even bumble bees aren't just one single species but about 46 in North America.

Augochlora pura on thistle
Nomada, cuckoo bee on spring beauty
Bee species vary not only in size but in many other ways. Some are active from early spring to the end of fall. Others complete their whole cycle in just a few weeks and remain dormant the rest of the year. Some are adapted to different climates. There are even some species, called cuckoo bees, that don't bother raising a family. Instead, just as cuckoo birds, lay their eggs in the nests of other bees. Some have a long tongue that enables them to reach into fairly deep throated flowers. Others can only visit flowers that are relatively flat and open. Finally, some are very particular about the flowers they visit. Only one species of plants or a few related species satisfy their needs.
Agapostemon splendens on seaside goldenrod

Lasioglossum pilosum on coneflower
Losing a few of these specialists may not be catastrophic, but it is preferable to preserve as many of them as possible. A rich variety of species confers resilience to an ecosystem. This is why it is important to have a wide range of specialists along with the handful of generalists.
Colletes on Cerceris canadensis
Bombus perplexus, confusing bumble bee on common milkweed
Long horned bee on sunflower





 All images © Beatriz Moisset


Monday, May 16, 2016

Early Spring Pollinators and their Flowers


Dandelion visited by a cuckoo bee
© Beatriz Moisset

Many gardeners are developing a new concern for pollinators. They look for ways to help them. Aware that a perfectly manicured, pesticide-laden lawn is not good for pollinators they enthusiastically adopt a scattering of dandelions in the early spring.

This is certainly beneficial to pollinators. However some of the passionate claims that accompany this activity are somewhat exaggerated. It is not true that pollinators “need” dandelions. They would prefer other flowers if they had a chance.

Spicebush in bloom
© Beatriz Moisset
Spicebush and pollinator
© Beatriz Moisset
Before dandelions were introduced from Europe and before lawns became so rampant in our suburbs, early spring pollinators were faced with a smorgasbord of early spring flowers. Here is an incomplete list of the so-called spring ephemerals prevalent where I live, in the Mid-Atlantic region: spring beauty, trout lily, trillium, columbines, rue anemones, Dutchman's britches, bloodroot and bluebells. These and others can still be found in nature areas, although they have become extremely rare in gardens and parks. Perhaps even more important to early spring pollinators are a number of trees and shrubs, such as willows, maples (some, not all of them), serviceberry, sassafras, spicebush, redbud, and a little later, azaleas and dogwoods, just to name a few.

Spring beauty and spring beauty Andrena
© Beatriz Moisset
This assortment of flowering plants offers a rich and diverse diet to newly awakened queen bumble bees, early Andrena bees, and other bees and flies seeking pollen and nectar. Some pollinators are specialists on just one or a limited variety of flowers. The spring beauty Andrena, trout lily Andrena and several willow blossom devotees would look at dandelions in despair, not being able to make any use of them.

Trout lily, frequently visited
by the trout lily Andrena
© Beatriz Moisset
The biotic community described above not only nourishes early-riser pollinators but also provides food and habitat for local wildlife. For instance, the red maple serves as a host plant for more than 100 moth species, willows provide food for several hundred species of moths. In turn, these caterpillars nourish birds and other wildlife. By contrast a lawn with dandelions is an impoverished ecosystem with very limited ecological value, more similar to a refugee camp than to a healthy, lively community.

Azalea and its specialist
the azalea Andrena
© Beatriz Moisset
If the goal is to help pollinators we would reduce the size of the lawn and grow some of the plants mentioned above rather than simply allowing dandelions among the blades of grass.

Bloodroot and Red-necked False Blister Beetle
© Beatriz Moisset
Such a goal is hard to achieve for most gardeners and probably impossible or nearly impossible for many of them. So, reducing the use of pesticides and allowing dandelions, as well as a few other small lawn “weeds,” is a good decision. But anybody seriously committed to protecting, not just pollinators, but entire ecosystems would do well to take a look at other alternatives.

Bluebells and carpenter bee
© Beatriz Moisset

Dandelion and ants
© Beatriz Moisset


Wednesday, May 11, 2016

Too Much Light!

Outdoor light
Most of it is wasted, aiming to the skies
© Beatriz Moisset

Could it be that we have too many outdoor lights? Night lights have become so abundant that they can be seen from space. Large cities are beacons made of myriads of tiny dots of light. The planet has never seen anything like it before. We know the benefits of good illuminated streets and public areas. Could there be some drawbacks too?

For one thing, we have lost the ability to see the night sky in all its splendor. Most stars have become invisible to city dwellers. Even in the suburbs and some distance from large cities, lights affect our vision of the sky. Astronomers regret this deeply and have some suggestions on how to mitigate the impact of night lights.

Night lights have other effects worth discussing. We all know that moths are attracted to lights. We often see a handful of them flying aimlessly around our porch lights or finally settling on a wall for the rest of the night. They are still there the next morning and remain still for the day since they are not day fliers.

How does this affect moths? Undoubtedly, such behavior may cost some of them their lives by exhaustion and lack of food. Does it matter?

Many moths are pollinators of night flowers. Nature is rich in its approaches to issues. Although most flowers bloom and are pollinated during the day, preferably when the sun is shining, a few take advantage of the darkness of dawn and dusk and even the middle of the night. Thus, they take advantage of certain flower visitors that have developed a similar strategy, namely being active at night.

Thyatira lorata moth
Attracted to night lights and
spending the day where it finally rested
© Beatriz Moisset
This is how a partnership has developed between some flowers and nocturnal moths. Ordinarily, such flowers are white or cream colored and have strong scents, better to attract their pollinators. Moths, in turn, have good night vision and a strong sense of smell.

Getting back to light pollution, if it kills moths, it too may be affecting the pollination of night blooms. We don't know this for sure, but there are strong indications that this is the case. Also some evidence points to night lights affecting the growth of some plants by getting their schedule confused.

We should follow the suggestions provided by several websites on how to minimize light pollution, for instance the Florida AtlanticUniversity website covers a lot of ground. One useful recommendation is "no light should be emitted above the source's horizontal plane."

The Mother Nature Network lists five ways you can reduce light pollution:
  1. Start with the light switch
  2. Check with your power company to see if you're paying for outdoor lighting
  3. Consider replacing outdoor lights with intelligently designed, low-glare fixtures
  4. Place motion sensors on essential outdoor lamps
  5. Replace conventional high-energy bulbs with efficient outdoor CFLs and LED floodlights
However most of these ideas, although excellent provide no significant protection to pollinators and their plants. For this purpose one valuable tip is to abstain from lighting the landscape. There is no real need to illuminate your trees, shrubs and the general area where they grow, so let us give up this kind of lighting, please.

Virginian tiger moth
© Beatriz Moisset




Friday, May 6, 2016

The Most Invasive Butterfly: Cabbage White Butterfly (Pieris rapae)

A flock of cabbage butterflies
(Pieris rapae)
© Beatriz Moisset
If you see a pretty white butterfly, more likely than not you are seeing an invasive species that was accidentally introduced to this country and to many other parts of the world more than a century ago.

The cabbage white butterfly is noticeable, pretty and soft, it visits gardens, meadows, you name it. Perhaps the only places beyond its reach are higher elevations. It starts flying early in the season and produces several generations throughout the summer and fall. No wonder it is seen so often.

Cabbage butterfly
(Pieris rapae)
© Beatriz Moisset
The name refers to the plant its caterpillar feeds on, cabbage. It also eats other members of the mustard family, such as cauliflower and kale and it is regarded as a serious pest. It also feeds on a number of wild, non cultivated mustards, including the invasive garlic mustard.

The cabbage butterfly is related to a group of native butterflies, the so called whites, yellows and sulphurs or family Pieridae. Their colors, as the names indicate are either whites or yellows. The caterpillars of most of them also feed on plants of the mustard family. A total of 58 species lived in North America before the arrival of this newcomer. Nowadays, the cabbage white is seen as often as all of them combined. One wonders if the growing numbers of this invader are having an impact on the populations of native Pieridae butterflies.

Orange sulphur butterfly
(Colias)
© Beatriz Moisset
In summary, it has the qualities of so called weedy species, with high rates of reproduction, very adaptable to different food sources and a variety of habitats.

Virginia white butterfly
Pieris virginiensis
© Beatriz Moisset
The cabbage butterfly reminds me of several insect species that were brought to this country intentionally or accidentally and proceeded to become incredibly widespread in a relatively short time. Now, some of them are more abundant than any of their native relatives. Here are a few examples: the Asian ladybug, the Chinese mantis, the giant resin bee, the European paper wasp, the drone fly, and the brown marmorated stink bug.

David Quammen, a distinguished journalist who has written extensively on conservation and ecology, has coined the term “Planet of Weeds,” meaning that the ecological changes caused by humans are having a severe impact on the flora and fauna of the entire planet. We had transported unprecedented numbers of species of plants, animals and bacteria beyond their natural distributions with the consequence that many of them have become established in their new surroundings. Not only do they become established but spread out from the original place of introduction, thus deserving the name of invasive species. They impact the local flora and fauna, bringing up the extinction of many species. In this way we are causing a mass extinction, comparable to some of the most serious mass extinctions of the past.

Specialist species are more vulnerable to extinction. The ones that have the best chance for survival are the weedy ones, the adaptable generalists. We are creating an impoverished world, gradually losing precious biological diversity, biodiversity for short. It may take millions of years for this biodiversity to raise back to the present levels. The human species may never see that.

Drone fly (Eristalis tenax)
One of many introduced, widespread species
© Beatriz Moisset

Sunday, April 24, 2016

The flower reinvented

Dichromena latifolia or Rhynchospora latifolia, identified by Andrew Greller.

Sedges and grasses are wind pollinated and have no showy flowers. It is interesting that Narrow-Leaf White-topped Sedge evolved to attract pollinators and created a sort of flower for this purpose. The apparent petals are not the same as those of a real flower but modified leaves called bracts.

See: Plant Profiles. White Top Sedge


Sunday, February 7, 2016

Native species

Common milkweed, Asclepias syriaca (© B. Moisset)
Definitions of native plants abound. None is entirely satisfactory in all circumstances but each may serve a specific function. Some strive for scientific accuracy; others serve practical purposes. Moreover, in some instances the nativity of a plant may not matter to the native-plant gardener. None of us is about to give up growing tomatoes regardless of their non-native status.

The Federal Native Plant Conservation Committee proposes the following definition: “A native plant species is one that occurs naturally in a particular habitat, ecosystem, or region of the United States and its Territories or Possessions, without direct or indirect human actions.” Such definition may be useful for policy making.

The Lady Bird Johnson Wildflower Center of the University of Texas at Austin provides a sampling of definitions. Here are two:

“Native plants should be defined as those that have evolved and adapted to a specific location and have remained genetically unaltered by humans” (Wasowski. The American Gardener, 1998).

“All indigenous, terrestrial, and aquatic plant species that evolved naturally in an ecosystem” (US Forest Service).

Some may prefer other definitions from that list. In my opinion, the best ones are those that recognize the significance of co-evolution, habitats and ecosystems.

In North America, 1492 is commonly used as the cut-off date. It signals the arrival of Europeans on this continent and also the subsequent era of exploration of the entire planet. We may regard it as an arbitrary date; but it is one with practical usefulness as well as with historical significance. The numbers of introductions of non-native species and the distances to which they are transported started growing dramatically in 1492 and continue to grow at accelerated rates.

Humans have been introducing species to other lands from the beginning of agriculture (and unintentionally even earlier). Polynesians took pigs to Hawaii more than a thousand years ago. In recent times, Europeans introduced a new breed on the island. Is one breed more native than the other? Does it matter? We need to remember that the recently introduced breed is larger in size, more invasive, and more destructive of habitats. Habitat restoration may justify eradication of the European introduction. But removing the earlier breed, which is embedded in Hawaiian tradition and culture, would not be wise. This thorny issue will have to be decided by Hawaiians. I don’t envy them the task or the heated conflicts that this issue creates.

The Three Sisters of Native American agriculture –corn, squash and beans– are not truly native to North America. They were first cultivated in a region of Mexico and Central America several thousand years ago and carried farther north and east as well as into South America in prehistoric times. It is tempting to regard these crops as native plants, but they are not really so. Once again, the question is: Does it matter? Would those devoted to conservation and restoration want to eliminate these non-invasive, economically significant, long-established crops? Of course, not! This is not the purpose of restoration.

Further back, all species of organisms have been on the move at a certain point. To grow and multiply is a mandate as old as life itself. Those that successfully multiply need to expand their territories and invade new areas. The present geographic distribution of any given species tells us only a small part of the story. To understand the concept of native organisms, we need some knowledge of the origin, evolution, and dispersal of species and taxonomic groups.

We can use as an example that quintessential native plant, the common milkweed (Asclepias syriaca) and its relatives, the other milkweed members of the genus Asclepias.
Common milkweed flower and one of its visitors, a bumble bee (© B. Moisset)
The family of milkweeds originated in Africa many millions of years ago. Its members have been spreading out ever since. They occupied Asia, evolving into a number of new species along the way. They crossed the Bering Strait around 30 million years ago and, once again, they diversified into a number of related species. Nowadays, there are more than a hundred species of the genusAsclepias in North America. Some crossed the Isthmus of Panama and invaded South America, where they evolved into a handful of species. I find it very interesting that many millions of years later a mammalian species would originate in Africa and follow a similar itinerary all the way to the tip of Patagonia in South America. I am talking about us, Homo sapiens.
Geographic distribution of Asclepias syriacaUSDA map
USDA maps illustrating the geographic distribution of species ofAsclepiasSee the complete page
The USDA maps show the distribution of the common milkweed, Asclepias syriaca, and of other members of the genus. The common milkweed is found in all the Eastern United States and Canada and also in parts of the West. Other milkweeds occupy more limited territories, some overlapping each other. We can be certain that their geographic ranges have not remained constant in the thousands of years of their existences. They responded to climatic changes that caused glaciers to expand and retreat by migrating north or south and by contracting and expanding their territories accordingly. Still, we regard them as native to the areas where they are naturally present.

Adult monarch on common milkweed (© B. Moisset)

Milkweeds didn’t come alone. They are part of ecological communities that include other species, some tightly, other loosely, linked. Milkweed butterflies, having tied their destinies to those of milkweeds, followed their host plants. The genusDanaus originated in Africa and spread out along with milkweeds covering similar territories. These were the ancestors of the monarch butterfly (Danaus plexippus) and its relatives.
Longhorn milkweed beetles (© B. Moisset)
In fact, the southern monarch (Danaus erippus), a resident of southern South America, is so similar to the North American monarch that both were considered members of the same species until recently. Curiously, this southern monarch, like its northern sister, is migratory. Even more curiously, it migrates south to a colder climate, when winter comes. This is the kind of natural history mystery that keeps me awake at night. I hope that somebody uncovers the secrets of the southern monarch and lets me know.Monarch butterflies are not the only insects that take advantage of milkweeds. A whole menagerie has evolved to feed on these plants. There are milkweed longhorn beetles, large and small milkweed bugs, milkweed weevils, and milkweed tussock moths, just to name the most familiar ones. All of them are adapted to the strong milkweed toxins. These poisons remain in their tissues and give them some protection against predators, which find them inedible.

Lady beetle larva, Coleomegilla (© B. Moisset)
However, despite the protection that the milkweed toxins provide to its feeders, some predators and parasites are adapted to this inconvenience. Several species of birds and mice feed on monarchs, both in this country and in Mexico, where they spend the winter. A number of predatory and parasitic insects also depend on monarch butterflies for nourishment. Thus the milkweeds and their dependents and the other components of the food chain are all linked together. They have been co-evolving for millions of years and are functional parts of their ecosystems.

Silver-spotted skipper (© B. Moisset)
These relationships matter when we talk about native plants. A non-native organism, one newly arrived into an ecosystem, lacks this kind of co-evolved interactions with the other members of the community. It is not a functional component of the ecosystem. Eventually, new interactions will develop given enough time. This may take tens of thousands or millions of years. This is why the best definitions of native plants involve the words “co-evolution,” “habitat,” “community,” or “ecosystem.”

In some instances, it is hard to tell what is native. In certain cases, it may not be important or practical to consider the nativity of a plant, as in the example of the crops grown by Native Americans. That which really matters is the long established and complex relationships present in ecosystems. A native plant is one that is ecologically linked to other components of the ecosystem where it is found.

Some important concepts lack a perfect definition. We need to name them, nonetheless. Biologists would be lost if they couldn’t use the concept of “species” just because no definition fits all the circumstances. This word is not only important but absolutely necessary. One may need to use different definitions of “species” depending on the discipline; but that is no reason to give up the word. The concept of “native” organisms is equally necessary. It is here to stay, regardless of the difficulties that may arise at times.
Robins are among the birds that sometimes eat monarchs (© B. Moisset)
Originally published by Native Plants and Wildlife Gardens

© 2012, Beatriz Moisset. All rights reserved. This article is the property of Native Plants and Wildlife Gardens.