State conservation agencies and state nurseries partner to provide landowners with trees for habitat, riparian zones, and other advantages. Here are photos from a tree planting last Friday along the upper Potomac River.
This week, we found out some "humbling" things about the tree of life, which has been redrawn to accommodate thousands of newly discovered forms of bacteria. Some people may be inclined to feel diminished by such advances in science, though this one could just as easily make people feel more elite, given that, unlike the bacterial multitudes, we’re made from many cells working together.
There are, however, a couple of features of the new tree that upend the way humankind sees its place in the cosmos -- features that are known to scientists but whose impacts have yet to work their way through the culture at large.
First, there is the fact that the tree has no "top." It’s more of a tumbleweed of life. The branches that lead to E. coli are as long as the ones leading to humans. There are no higher or lower organisms any more than there are higher or lower cousins in a genealogical tree.
Beyond that, the tree of life is still growing. When human activities lead to the extinction of a plant or animal, a whole branch is severed. The extinct animal or plant
Some Animals Are More Equal than Others: Keystone Species and Trophic Cascades
Summary
Keystone species and trophic
cascades are fundamental concepts in ecology. This short films tells
the story of how these concepts were first established through the
pioneering experiments of two young researchers: Robert Paine and James
Estes.
The short film opens with two questions: “So what determines how
many species live in a given place? Or how many individuals of the
species can live somewhere?” The research that provided answers to these
questions was set in motion by key experiments by ecologists Robert
Paine and James Estes. Robert Paine’s starfish exclusion experiments on
the coast of Washington state showed that removing starfish from this
marine ecosystem has a big impact on the population sizes of other
species, establishing the starfish as a keystone species. James Estes
and colleague John Palmisano discovered that the kelp forest ecosystems
of the North Pacific are regulated by the presence or absence of sea
otters, which feed on sea urchins that consume kelp. These direct and
indirect effects of sea otters on other species describe a trophic
cascade. These early studies were the inspiration for hundreds of
investigations on other keystone species and trophic cascades, as well
as ongoing studies into the regulation of population sizes and species
numbers.
Foxes That Endure Despite a Lack of Genetic Diversity
An island fox. Researchers say one community of the species has the least genetic variation in a sexually reproducing species.Credit
Chien Lee/Minden Pictures
The
Channel Islands, off the coast of Southern California, are a natural
laboratory for a particularly adorable experiment in evolution.
A
unique species called the island fox has lived there for several
thousand years, shrinking over the generations until now each is smaller
than a house cat. Adult island foxes weigh as little as 2.35 pounds.
Now a team of scientists has discovered another way in which island foxes are extraordinary: Genetically, they are nearly identical to one another. In fact, a fox community on one island has set a record for the least genetic variation in a sexually reproducing species.
Oliver
A. Ryder, the director of genetics at the San Diego Zoo Institute for
Conservation Research, said the new research posed a biological puzzle.
It’s
an axiom of evolutionary biology that low levels of genetic variation
put species at risk of extinction. Yet the delicate island foxes are
still racing across meadows and bounding up trees.
“How can the island foxes get away with it?” asked Dr. Ryder.
The
new study, published on Thursday in Current Biology, was led by Robert
K. Wayne, a geneticist at the University of California, Los Angeles. Dr.
Wayne has been studying the DNA of island foxes since the early 1990s,
hoping to understand their remarkable makeup.
“They’re like dodos,” Dr. Wayne said in an interview. “They have no notion of human fear. You can just put them in your lap.”
Some scientists suspect that island foxes are fearless because of a long relationship with humans.
Native
Americans first settled the islands about 13,000 years ago, and they
may have brought along gray foxes from the mainland. Previous studies
indicate that island foxes share a common ancestor with gray foxes that lived 9,200 years ago.
It’s
unlikely the foxes made the trip on their own; the islands are
separated from the mainland by 12 to 70 miles of open ocean. Another
clue pointing to human help: Native Americans painted foxes on rocks and
gave them ceremonial burials. Foxes may have had a spiritual importance
to them.
However
the animals arrived on the Channel Islands, they adapted quickly. The
oldest island fox fossils date back 7,000 years and show that they were
small even then. The Great Shrinking required less than 2,200 years, it
seems.
Dr.
Wayne has focused on genetic variation among the island foxes. He and
his colleagues started off by examining a few genetic markers, finding
striking similarities between the animals. But the scientists couldn’t
be sure just how similar the foxes were until technological advancements
made it possible to sequence their entire genomes.
There
are six subspecies, each living on a separate Channel Island. In their
new study, Dr. Wayne sequenced the genome of one fox from each of five
subspecies. On the sixth island, San Nicolas, they sequenced two
genomes.
Like
other animals, island foxes carry two copies of each gene, inheriting
one copy from each parent. In large populations with a lot of genetic
variation, there can be many versions of any given gene. An animal may
inherit two varying copies of a gene from its parents.
But
the scientists discovered virtually no differences in the DNA the foxes
had inherited. “We call it genetic flatlining,” Dr. Wayne said.
While each subspecies has very little diversity, the foxes on San Nicolas are almost like identical twins, a record.
Low
genetic variation can pose a serious threat to survival. When a new
threat appears — a new disease, for instance — some individuals may have
the genes to resist it while others lack them. In a population with low
genetic variation, none of the animals may have the right genes to
survive.
Inbred
populations also often share mutations that are bad for health,
shortening life spans or reducing the number of offspring. Dr. Wayne and
his colleagues found that island foxes have many more harmful mutations
than gray foxes on the mainland.
On
the face of it, the island foxes should have vanished long ago. “But
that hasn’t happened to them in thousands of years,” Dr. Wayne said.
“They’re an exception to the paradigm.”
Dr.
Wayne speculated that island foxes might enjoy some sort of special
protection. It’s possible, for example, that as top predators on a small
island, they didn’t have to face the challenges that other inbred
animals do. Or perhaps the people who lived on the islands even helped
them survive.
Or,
while the genes of island foxes may be almost entirely identical, maybe
they are activated in the animals in varying patterns. Experiences
early in life can program genes to switch on and off, a phenomenon
called epigenetics.
“It might also be some combination of all of the above,” Dr. Wayne said.
Other
researchers suggest that island foxes had been protected in more
familiar ways. Newly arrived foxes could have rejuvenated the Channel
Island gene pool with some fresh variation.
“Their
study has not ruled out occasional immigrants reaching the islands,”
said Richard Frankham, a geneticist at Macquarie University in
Australia.
But Dr. Wayne said his new study cast doubt on that possibility.
Each
subspecies of island fox is genetically distinct, showing no sign of
newly introduced genes moving from island to island. “There’s no
evidence of gene flow,” Dr. Wayne said.
Understanding
the evolutionary history of the island foxes is important to ensuring
they have a future. A rapid population decline led to four subspecies of
island foxes being declared endangered in 2004.
It’s likely that several causes helped drive down their numbers.
In
recent decades, golden eagles have arrived on the islands and begun
killing off the foxes. They have also faced new diseases introduced by
raccoons and other invasive animals.
Island fox pups on Catalina IslandVideo by Karl Huggins
Some
researchers are concerned that their genetic similarity could increase
the risk. “If we care about the persistence of island foxes and other
small populations, we should be concerned about low genetic variation,”
said W. Chris Funk, a biologist at Colorado State University.
Writing in the journal Molecular Ecology last month, Dr. Funk and his colleagues suggested one way to help the foxes: move animals between the islands. If the subspecies mix genes by interbreeding, they may be able to increase their variation.
Scientists have already used this procedure, known as genetic rescue, to help other species. In Florida, for example, the resident panther population
has had a difficult time producing new cubs. Researchers introduced
panthers from Texas, and their new genes have helped the Florida panther
population grow.
Based
on his new research, Dr. Wayne said he didn’t think island foxes need
genetic rescue, at least until scientists find strong evidence that they
are suffering because of low genetic variation.
“I
would really hesitate to move foxes around,” Dr. Wayne said. “Each
island is genetically distinct. I would be loath to destroy that.”
Arlington County, Virginia is very urbanized. Due to loss of wetlands (including vernal pools) and heavy development, half the frog and toad species that used to live in Arlington are now gone. The remaining species are often in small, isolated populations, in only a handful of locations.
Frogs and toads are excellent bio-indicators of environmental health. Since they consume plant material when young and then switch to a predatory diet, they can build up toxins in both diets. Since they can also absorb chemicals and pollutants through their skins in all stages of life, they are also very sensitive to changes in the environment. So loss of frogs and toads can point to an unhealthy environment and their declines can serve as a warning about the state of the habitat.
In addition to having cleaner water and preserving our wetlands, the control and management of invasive plant species has allowed the habitats to support more insect food. Native plants that have also been making comebacks support more insect prey than the exotic invasive plants (and these insects then feed so many more animals such as most of our bird and all our bat species).
Some of our frogs needed a bit more help in getting established. Such was the case for our Wood Frogs which are dependent on mostly fish-free vernal ponds and mature woodlands. For the longest time Arlington only had two places where they bred. In time, the population from Long Branch Nature Center eventually made it into Glencarlyn Park on its own. But since these frogs need mature woods and vernal ponds that may not be close to one another, we assisted in establishing new populations.
