Ants

Living in the chapparal means that you're living amongst animals of many kinds: birds, lizards, snakes, mammals, and insects. Most of these animals we cherish, and in fact we go out of our way to attract them to near our home so we can view them — we put out several kinds of seeds, suet, cracked corn, sugar water (for hummingbirds and orioles), and fresh water to lure all the animals.

But some of these animals are ... less desirable ... to have near our home. Mountain lions, though beautiful, are dangerous to our pets and possibly even to us. Rattlesnakes are less dangerous than their reputation, but still not exactly fun to share your yard with. Skunks, well, you know. Coyotes can be a problem, especially with pets. And there's an insect here that strikes fear into many people: the "tarantula hawk" (actually a wasp). But if you were to ask my wife to make a prioritized list of all the beasties she loves to hate, ants would be near the top, I'm sure.

Ants are marvelous little "machines" for finding food. And out here in the dry, near-desert of the chapparal, they've also honed their skills at finding water. Especially in the dry part of the year, they find some way to get into our home — where they're sure to find some sort of ant treat around. Next thing you know, there's a zillion ants crawling all over in a zig-zag track, piling up on whatever they found attractive. Might be a cup with some water in it, or the water left at the bottom of the dishwasher, or one of the pet's food bowls, or some leftovers that we forgot to send down the disposal. Whatever little morsel there is, those darned ants are going to find it. And for this survival skill they have earned Debi's eternal enmity.

But if you can get past the ... inconvenience ... of ants, there are some interesting things to know about them.

For instance, it's pretty obvious that ants, as a group, are very successful. But you may not be aware just how successful they are. If you measure success by the total weight of a group of animals, then scientists will tell you that ants are either #1 or #2 amongst all kinds of animals (if you include termites in with ants). From the proceedings of the National Academy of the Sciences:

Ants are arguably the greatest success story in the history of terrestrial metazoa. On average, ants monopolize 15-20% of the terrestrial animal biomass, and in tropical regions where ants are especially abundant, they monopolize 25% or more. But ants did not always run the world. They do not appear in the fossil record until the mid-Cretaceous, and for more than the first half of their history — a period spanning 60 to 80 million years — ants occupied a relatively modest position in the terrestrial biosphere. To understand the factors, both ecological and historical, that contributed to the rise of the ants, we require a clearer picture of the stepwise evolution of the major ant lineages. Now, Grimaldi and Agosti report in a recent issue of PNAS the remarkable discovery of a worker ant, preserved in amber for over 90 million years, that is clearly assignable to a modern ant subfamily that contains many familiar extant species, including carpenter ants. Combined with other paleontological and phylogenetic information, this unexpected fossil strongly indicates that the diversification of many ant subfamilies occurred earlier and more rapidly than previously suspected.

Ants represent the family Formicidae in the insect order Hymenoptera and, like the yellow jackets, hornets, and paper wasps to which they are closely related, ants are stinging wasps. All ants are eusocial, that is, they live in colonies in which a wingless neuter daughter caste cooperates to raise subsequent generations of their mother queen's offspring. Like all of its descendants, the ancestral ant was almost certainly eusocial, with colonies made up of small bands of hunter-gatherers living in simple temporary nests in the soil. From this modest beginning arose the current diversity of the family Formicidae, numbering over 9,500 described species and an estimated 3,000 to 9,000 additional species as yet unknown to science. Today ants occupy keystone positions in most terrestrial environments, serving as major conduits of energy and organic material. They are, for example, important turners of the soil, matching or exceeding the activity of earthworms in this role. They are among the leading predators of invertebrates in most ecosystems, and in the Neotropics they are the leading herbivores as well, with leaf-cutter ants taking more than 15% of the fresh vegetation (feeding it to a symbiotic fungus, which they in turn eat). Interactions with ants have shaped the evolution of diverse organisms to an astonishing degree. Ants participate in symbioses — some facultative, some obligate — with over 465 plant species in over 52 families, with thousands of arthropod species, and with as-yet-unknown numbers of fungi and microorganisms. Clearly, the study of most ecosystems must include the study of the resident ant species. Because of their complex colony-level behaviors, ants serve as model organisms for the highly visible disciplines of behavioral ecology and sociobiology, particularly in studies focused on the dynamics of kin selection, within-colony conflicts of interest, caste differentiation, and division of labor.

When you consider how many ants it would take to equal the mass of a single human, and then consider that there are something like 6 billion humans — it's a little difficult to even imagine the number of ants it would take to exceed the weight of all humans. But there really are that many ants, and more — depending on whose estimate you want to believe, the ants weigh somewhere between 2 and 8 times as much as humans!

Wikipedia has an excellent article (with good links) on the Earth's biomass, and the Mad Scientist Network has this article about the biomass of ants.

Of special interest to Debi are things that eat ants. Especially if the ant suffers a little in the process. As you might expect for anything that makes up a goodly percentage of the Earth's biomass, lots of animals of various kinds have decided that ants can be tasty. The preceding link goes to Dale Ward's website, which (amongst other things) has lots of good information about ants.

Lunar Librations

After my recent post on the Harvest Moon, a friend emailed me with this:

I'm somehow disappointed with your picture of the moon at apogee and perigee. The non-circular orbit also has the effect of producing lunar librations so we can see more than 50% of the moon. I can't help but think this is in sync with the apogee and perigee of the moon so the two images should look different (the two extremes) instead of being a 30% reduction of one another. But I'm just guessing...

The animation at right (shamelessly ripped from Astronomy Picture of the Day, but modified to slow it down) shows the lunar libration my friend speaks of. I, too, knew of the librations without really understanding the mechanism behind them. My friend's email nudged me into a little research.

My initial guess about lunar libration was that these two things caused it:

1: The tilt of the lunar orbit (5.2 degrees) with respect to the earth's rotation, coupled with the latitude (on the Earth) of the observer. This slightly "tilts" the view an observer has, to see slightly past the north or south pole.

2: The displacement of an observer viewing the moon at moonrise versus an observer at moonset. This would allow an observer to see slightly past the nominal east and west sides of the moon.

It turns out that both of the mechanisms I described above do contribute to libration (both latitudnal and longitudinal), but I completely missed two other mechanisms, the first of which causes the most libration:

1: The moon's rotational rate is constant, while its speed in its orbit about the Earth is variable. More on this below.

2: The moon's rotation is tiled about 1.5 degrees to the plane of its orbit. This adds another 1.5 degrees to the first effect I had guessed, for a total of 6.7 degrees.

For me the most interesting of these four mechanisms is the one that has the biggest effect, and that I had completely missed. It depends on a marvelously subtle interplay between the moon's constant rotational speed and variable orbital speed. As my friend guessed, the ellipical (non-circular) orbit of the moon is the cause of this — but the effect is the opposite of what he guessed: at apogee and perigee, there is no libration at all!

This unexpected outcome derives from the characteristics of an elliptical orbit. At perigee (the point of the moon's closest approach to the Earth) the moon is moving faster than at apogee (the point of the moon's farthest distance from Earth). The way I puzzled this out was to divide the moon's orbit into quarters, with one dividing line from perigee to apogee, and the other at 90 degrees to that. Starting at the perigee, let's call the quarter-orbits I, II, III, and IV. The moon is observably at dead center (with respect to longitudinal libration) at both perigee and apogee. To explain the longitudinal libration, let's follow the moon through the four quarters of its orbit:

Quarter I: The moon starts at perigee, where it is moving faster than at any other point in its orbit. During this quarter orbit, the moon will slow down some, but it's still moving faster than the average speed over the entire orbit. This means that the moon reachs the end of the first quarter of its orbit in slighly less than one quarter of the time it takes for an entire orbit — so the moon will have rotated slightly less than one quarter of a rotation. In fact, it turns out that the moon at this point has only rotated about 82 degrees — thus providing a view for an Earth-bound observer that is 8 degrees (90 - 82 = 8) of longitude shifted.

Quarter II: The moon is moving further from Earth, and is slowing down. At the end of this quarter, it has moved through exactly half of its orbit, and it has rotated through exactly half its rotation — so no longitudinal libration.

Quarter III: The moon is moving closer to Earth, and is speeding up. However, its speed during this quarter is lower than the average speed over the entire orbit. That means that the moon takes slightly more than one quarter of an orbital period to reach the end of this quarter orbit. Because of that, the moon has rotated slighly more than one quarter of a rotation — about 98 degrees instead of 90. That means that an Earth-bound observer has a view that is shifted 8 degrees (90 - 98 = -8) longitudinally, in the opposite direction as occurred in quarter I.

Quarter IV: The moon is moving closer to Earth, and is speeding up. At the end of this quarter, it has moved through its entire orbit, and it has rotated exactly once — so no longitudinal libration.

I'll bet that was more than most of you ever wanted to know about lunar libration! But if you're anything like as loony as I am, you can find more information about lunar libration here, here, here, especially here, and here.

Veggie Lunch

Our local stores and produce stands have had really nice asparagus and Brussel sprouts the past few weeks. Debi picked some of each up on her last shopping, and today we had an all-veggie lunch: just fresh asparagus and sprouts, with a little butter and salt.

Oh. My. God.

They were so good!

Up to now, the only thing I've ever had that tempted me into a homogenous diet was sushi. Fresh veggies of this quality are the second...

Sycuan Peak

Sometime last year I discovered that we had a nature reserve practically in our own back yard. It's called the "Sycuan Peak Ecological Reserve", and it's part of the state system of reserves, managed by the California Department of Fish & Game. Sycuan Peak itself is smack in the middle of this reserve, just southwest of Loveland reservoir. The southern edge of the reserve borders Lawson Valley Road, just three miles from our home.

Within a hundred feet or so of the 2.5 mile marker on Lawson Valley Road is an unmarked (though there used to be a sign) rugged four-wheel drive road up the small peak to the north. This is the "trail" to Sycuan Peak, actually an old and heavily eroded jeep trail. Much of the road is actually still drivable by four-wheel (though I don't believe you're actually supposed to drive on it), but toward the top it's pretty much impassable by vehicle. This morning Jim Barnick and I hiked up to the peak with our two dogs (Mo'i and Lea); this was the first time we'd ever done so.

The trail is just a mile long, but steep, with an 850 foot elevation gain in that short distance. The views all along the trail are spectacular, perhaps especially for someone living in that area. From the top we had the best view of Loveland Reservoir that I've ever had from the ground (first photo). The view to the north included a great view of Cajon Mountain (second photo). To the west we had a spectacular, nearly uninterrupted view of the Pacific coastline — only Miguel Peak punctures the horizon from Sycuan Peak, and by less than a degree. The skies were a bit hazy today, especially to the west; we'll do this again on a really clear winter day and I'll take a panorama.

Our dogs thoroughly enjoyed this hike. No surprise there! But one thing that was a little surprising: our agile little female (Lea) actually got a little tuckered out on the way up. She usually tries to pull us up the hill whenever we're walking with her; she's incurably eager to see what's around the next bend. This time, though, she started slowing down at around the 2/3 mark — enough so that I got concerned she might be overheating or something, and we stopped to rest. That was the cure — a few minutes standing still and she was good as new. At the top we gave both dogs a nice drink by pouring water into our cupped hand. Both of them had a little trouble figuring that out <smile>.

One interesting factoid about the Sycuan Peak Reserve: it is the primary remaining habitat for a very rare plant: Nolina interrata, commonly known as the "Dehesa Beargrass". From the U.S. Fish and Wildlife Service site:

A total of about 9,000 Nolina interrata plants are known (FWS 1998a, TNC 1998).

There are nine populations of Nolina interrata in San Diego County, all within a 15.6 square km (6 square mile) area in the Dehesa Valley, immediately east of El Cajon, California and from three small, somewhat disjunct populations in northern Baja California, Mexico. There are no records of extirpated populations (FWS 1998a, TNC 1998).

About two-thirds of all populations, and 90-100 percent of all major populations, are protected on reserve lands owned and managed by The Nature Conservancy (TNC) at McGinty Mountain and by the California Department of Fish and Game (CDFG) at Sycuan Peak. The protection afforded by the establishment of the Sycuan Ecological Preserve occurred subsequent to the proposal to list Nolina interrata. The remaining few occurrences are small and are on private lands (FWS 1998a).

Jim and I did not search for this plant during our hike; we'll save that for another day. Not being plant experts, I suspect we may have a little trouble positively identifying it even if we did manage to find it <smile>.

Nine thousand individuals sounds like an extremely small population, at risk all the more because they're located in just a few concentrated populations. The FWS web site mentions that Nolina interrata flowers profusely after a fire; parts of the Sycuan Peak Reserve (if I have got the borders correctly) burned in the Pines fire of 2001. We can hope for a bit of a comeback from that. Also in the FWS web site is mention that at least one of the isolated populations appears to be composed entirely of genetic clones of one plant; another risk factor. There's more information on this plant (including photos) here, here, and here.

The geocachers have discovered Sycuan Peak as well. Jim and I didn't try to find this particular one, but it's clear from the description that it's somewhere very close to the peak.

As usual, click on the photos for a larger view.