Wednesday, April 7, 2021

Table Rock Revisited

Spring is the best time of year to hike up either of Southern Oregon's Table Rocks. The sky is blue and fresh, life has returned to the land after a grey winter, and the humming of insects fills the air. Flowers are the jewels of the experience, since they are the epitome of Spring.
A mining bee (Andrena)
Part of what makes Upper Table Rock enjoyable to hike is that it's relatively quick and easy, not to mention very close to where I live. It takes less than an hour to reach the top of the mesa. Of course, with my camera I tend to stop and snap a few photos every time I see something interesting so it often means I spend most of the day exploring.
Erythronium hendersonii
Shortly after setting out on the trail, Erythronium hendersonii takes center stage. It was in bloom as far as I could see in the forest understory on the first half of the ascent. I advise getting on your hands and knees to check out the intricate floral markings! These nectar guides may help bees (the primary pollinators of Erythronium) find the nectar reward at the intersection of the petals.
A carpet of Erythronium
Inexplicably, bees were largely absent from most of the flowers lower on the trail. A few factors may have contributed to this. The manzanita was blooming further up the plateau, and the bumblebee queens which I suspect are the primary pollinators of erythroniums here were busy looking for suitable nest sites. One can only imagine.
Apis mellifera
As I continued to ascend the trail, honey bees became more prevalent on the erythroniums. Perhaps they've replaced the ancestral bumblebee pollinators. Maybe the bees which once pollinated E. hendersonii are now extirpated. Ranges of species change all the time, at least in evolutionary timescales. Many species of bumblebees have been seeing declines in recent decades due to habitat loss and diseases spread by introduced species. This is purely conjecture.
Honey bees appear to be adequate pollinators of E. hendersonii. The stigma is situated in a way that simply jostling the flowers (such as a bee landing on the stamens) may cause some pollen to move around. Most of the erythroniums that I've encountered in the Rogue Valley set seed every year despite potentially low numbers of pollinator visits. This apparent ability to set seed easily may be an adaptation to unpredictable spring weather. It's around this time of year that rain becomes an oddity and the next time water falls from the sky is autumn. Time to dry out.
Protosmia rubifloris ♂ hiding in Ranunculus occidentalis
The abundance and variety of bees now is astonishing. Protosmia is an osmiine bee (Megachilidae, leafcutter, mason, and resin bees) that nests in above-ground cavities. Records of nest sites is sparse, but some species have been known to make nests in things such as pine cones and snail shells! Another trait that makes Protosmia fascinating is that they overwinter as adults, uncommon in the Megachilidae. Their nests are capped with an excreted resin. Another peculiarity is that not all bees favor buttercups (Ranunculus spp.), and the pollen is even toxic to some bees.
Anthaxia aff. inornata
It is likely beetles are often overlooked as pollinators. They're not as efficient, or perhaps charismatic, as bees. Beetles were pollinating gymnosperms like cycads at least 200 million years ago, at least 75 million years before angiosperms (flowering plants, plants most adapted to bee pollination) and bees every appeared in the fossil record. Many flower-visiting beetles don't travel from flower to flower as frequently as bees, but there are some with densely haired bodies which are important pollinators of some plant groups (including many of the large-flowered tulip species), many bearing bowl shaped magnolia-like blossoms.
Flower longhorn beetle (Cortodera)
Beetles visit flowers for a variety of reasons, though I don't know of any beetles that collect pollen for rearing young. Many beetles eat pollen, nectar, or the flowers themselves. In other instances, beetles congregate at flowers to mate. There are also parasitoid beetles which lay eggs on or near flowers, the larvae attaching themselves to bees to hitch a ride to the nest where they feed on the provisions supplied by the bee or the bee larvae.
Ranunculus austro-oreganus
Southern Oregon buttercup (R. austro-oreganus) are endemic to, unsurprisingly, Southern Oregon (specifically Jackson County, according to the NRCS). They are slightly larger than R. occidentalis, and they have reddish veins on the back of the petals. Upper Table Rock hosts a vigorous population on the first half of the trail.
A hidden Lasioglossum ♀ forages on Southern Oregon buttercup.
I'm always intrigued by bees that visit buttercups. Many of the bees that collect ranunculus pollen are specialists, and the pollen would be toxic to many bees unable to metabolize it (Praz et al. 2008). That said, seeing a bee on a buttercup seems like something special. Pollen specialists need the pollen from their host plant in order to rear the next generation, which elucidates why maintaining a healthy balanced ecosystem is so crucial. Lives literally depend on diversity.
Fritillaria recurva
One plant that always results in a gasp is the beautifully checkered Fritillaria recurva, sometimes called red bells. Upper Table Rock sports a scattered population of the gloriously red bulbs. I have never once seen pollinators of any kind visit the flowers, but it isn't terribly surprising since I have never seen more than a dozen of them flowering in one place. Pollinators, particularly bees, are generally most attracted to large patches of flowers of the same species. The most F. recurva flowers I have seen in one place is maybe a little over a dozen. Besides all that, the morphological characteristics of the flowers suggest Ornithophily (bird pollination). Red tubular or bell shaped flowers with dilute nectar and slightly protruding stamens fits the bill. [Pun was accidental]
Fritillaria recurva is one of the most graceful native wildflowers, and it's always a treat to find in the wild. I hope to someday see a hummingbird visiting the flowers, but due to a lack of photos of pollination events on the google, I may be in for a bit of a wait.
Habropoda depressa ♂ on Cynoglossum grande
Another woodland favorite is the Pacific hounds tongue (Cynoglossum grande); a bigger, sexier version of the familiar forget-me-not (Myosotis) grown in cottage gardens. Being a member of the Boraginaceae (you guessed it, the borage family), it has white fornices (the white appendages at the "eye" of the flower, sing. fornix) and hidden anthers. Bees collect pollen by sticking their tongues in the flower, and some have specialized hooked hairs on various parts of the proboscis for this purpose.
Habropoda depressa 
Habropoda depressa, sometimes known as mountain digger bees, are some of my favorites. As the name suggests, they are solitary ground-nesting bees. Despite being solitary, they nest in large congregations. Males are the first to emerge, so the first to see foraging for nectar as they wait for the females. As the unfortunate females emerge a week or two after the males, they are balled by thirsty males trying to mate. I observed such an occurrence recently. The males numbered probably a dozen per female, and females couldn't even get off the ground before being mobbed. This doesn't appear to hurt the bees, despite some grappling between males, and they seem to have very healthy populations here.
Andrena on Lomatium urticulatum
Mining bees (Andrena spp.) are the most common spring bees on Upper Table Rock. Spring gold (Lomatium urticulatum) is the first of the buscuitroots to bloom, sometimes starting in mid February. Small bees and flies are quite smitten.
Ants are one of the least likely pollinators, despite many species seeking nectar on a huge variety of plants. Their ability to be good pollinators is sometimes hindered by pollen-destroying excretions on the exoskeletons of some species. Many ants produce antibiotic compounds needed to keep pathogenic microorganisms out of the nest. Pollen that comes into contact with these compounds is often no longer viable, and ant pollinated plants see a decreased seed set when compared to bee pollinated plants. See Beattie et al. 1984.
Andrena males on Lomatium californicum
Larger lomatiums grow in clearings along the trail on Upper Table Rock. The inconspicuous green flowers are highly sought by small mining bees. Andrena are short tongued bees, having relatively short labial palpi and glossa (for detailed diagrams of bee mouthparts see Bee Anatomy, it's a European bee ID website but the diagrams are good for all bees). The glossa can be thought of as the true tongue, the part that laps up nectar. In general, short tongued bees need flowers with easily accessible nectar and shallow flowers. Lomatiums and many genera in the Apiaceae (carrot family) offer numerous small flowers which are attractive to many small beneficial insects.
Andrena ♂
Andrena are mostly solitary, but many are thought to be communal. This means the females share a nest entrance but dig and provision their own cells which radiate laterally off the main burrow. Andrena line their cells with a wax-like substance, possibly to keep water or pathogens out. Males are sometimes seen before females, but they both usually emerge at the same time. Both male and female overwinter as adults, though the females mysteriously hide after mating, perhaps returning to the burrow to start digging cells. Andrena are univoltine, meaning one generation is produced per year. More on Andrena later.
Micranthes integrifolia with a fly
Micranthes, formerly Saxifraga, is seen periodically on both Table Rocks. It appears to be attractive primarily to various flies, as I suspect most saxifrages are.
Buckbrush (Ceanothus cuneatus)
At the time of my hike on Upper Table Rock, the buckbrush was just about to bloom. (By thy time I finish writing this, the bloom will probably be passed.) The very first of the musky smelling ceanothus blooms were attractive to honey bees. The only open buds were on the sunny south side of the shrubs. Sunlight is a key indicator to many plants that it is time to bloom, be it day length or plain old warmth.
Birch leaf mountain mahogany (Cercocarpus betuloides)
I've probably walked by these trees in bloom a hundred times in complete ignorance. The greenish inconspicuous flowers of mountain mahogany were attractive to bumble bees and honey bees, and the buzzing was the only indicator to me that they were blooming.
A honey bee grooms pollen into her corbicula
The ten to twenty foot tall trees periodically grew along the Upper Table Rock trail. Mountain mahogany is common in the Western states, growing in dry mountainous habitats from Canada south to Mexico. The seeds are very distinctive, and I've seen them for years not knowing what made them. Mountain mahogany seeds float down with a spiraled fuzzy tail, similar in function to the wings on maple seeds, aiding the seeds in spiraling away from the parent plant. Upper Table Rock trail in the fall is teeming with the peculiar curly-tailed seeds.
California sandwort (Minuarta californica)
Upon reaching the top of the mesa, I was rewarded with a carpet of miniature blooms spanning as far as I could see.
Apis mellifera
Bees were everywhere. I had seed the occasional honey bee, but the vast majority of the bees on the summit were small native bees. Every time this honey bee landed on a flower it bent it over.
The majority of bees on the top of Upper Table Rock were small natives, mostly Andrena. These small bees, roughly half the size of a honey bee, are completely silent in flight. Honey bees, in contrast, are noisy and buzz every time they fly. This is a common phenomenon when comparing colony-forming Hymenoptera with solitary Hymenoptera. Colony forming bees (i.e. honey bees, bumble bees) and wasps (i.e. yellowjackets) are noisy and conspicuous, often brightly colored. This is an aposematic warning to would-be predators that they can and will defend themselves.
Solitary bees (i.e. mining bees) and wasps (i.e. braconids) are often quiet in flight, and often have dull colors. These bees would rather flee than fight. Compared to honey bees, many solitary bees have relatively little invested in their nests and can readily relocate, abandoning a compromised nest. Nests of honey bees, bumble bees, and yellowjackets (among others) are full of hard earned resources (i.e. wax/paper comb) and multitudes of developing larvae. If these social Hymenoptera were forced to abandon their nests, it may be a death sentence. Solitary bees, like Andrena, aren't well equipped to defend the nest from large predators, so they don't advertise it.
Andrena collect pollen dry, without mixing it with nectar like honey and bumble bees do. Specialized hairs called scopae are found on the back legs of Andrena all the way from the tibia all the way up to the propodeum (the rear, bottom portion of the thorax). Pollen appears to wrap around the underside of their waist, like a belt. While this dry collected pollen has a better chance of becoming dislodged on a flower (unlike wet honey bee pollen), it is estimated that less than 5% of the pollen is used for pollination. That means that at least 95% of the pollen collected by bees is eaten. This makes me wonder, do plants even want bees to collect their pollen?
Male Andrena were common at the time of my hike. Their long antennae are used to detect potential mates. Males don't collect pollen, and their utility as pollinators is questionable. However, we can thank the males for creating the next generation of Andrena! Thanks guys. Your bee-havior has not gone unnoticed!
Lasioglossum (subg. Lasioglossum)
Sometimes known as the sweat bees, Lasioglossum are probably the most abundant and diverse bees in North America, often very small and inconspicuously colored. They range in sociality from true solitary to primitive eusociality, sometimes varying geographically possibly in response to resource availability. Nearly all Lasioglossum nest in the ground, and some can have multiple generations a year with some overwintering as adults and some overwintering as larvae. There is a lot of mimicry between species which can make identifying Lasioglossum to species very challenging, something I hope to get better at this year.
Lasthenia californica ssp. californica with male Andrena
More Andrena on dwarf daisies on Upper Table Rock, shocking! The common name for Lasthenia, goldfields, is extremely accurate. Large swaths of golden honey-scented daisies carpeted the mesa summit intermixed with California sandwort. Goldfields vary in height from less than two inches up to fifteen inches depending on the soil. The soils atop the Table Rocks is thin and probably deficient in nutrients, resulting in dwarf versions of otherwise foot-tall flowers. L. californica is native throughout the West Coast from Southern California to Southwestern Oregon, mostly on the western halves of the states.
It would be interesting to learn whether different species of Andrena prefer different plant species blooming concurrently. I didn't collect any specimens during my hike, but it would be interesting to investigate in the future. Many Andrena are pollen specialists of Asteraceae and even single genera or species. Pollen specialist means the females collect pollen from a narrow range of genera or species, but may collect nectar from a wider array of plants. Goldfields (Lasthenia) are host plants to at least a few species of Andrena (see Thorpe and Leong 1998).
Plagiobothrys aff. nothofulvus
Popcorn flowers, Plagiobothrys spp., are host plants for a ton of native pollen specialist bees in Oregon. I saw many patches of popcorn flower in various parts of the Upper Table Rock hike. I didn't see any bees, but I didn't observe for long. Pollen specialists of many members of the Boraginaceae (the forget-me-not family) have special adaptations for collecting the pollen hidden in the flowers. Some of these bees have velcro-like tongues with specialized hooked hairs on the proboscis. So cool!
Allium parvum
One of the treats I always look forward to on Upper Table Rock are the diminutive onion flowers which sit on the ground, often against volcanic stones. Allium parvum is a tiny onion with pea-sized bulbs. The leaves are often dead or dying by the time the flowers open.
Collinsia sparsiflora
Another dwarf version of an otherwise taller species, the odd-named spinster's blue-eyed Mary. In better soils, these plants can grow up to a foot tall, though on the thin rocky soils of Upper Table Rock they are less than two inches. Small three-square foot patches variously carpeted the mesa summit. Oddly, I witnessed no bees on these flowers. Peculiar.
Cowbag clover (Trifolium depauperatum var. depauperatum)
I'm always amused by the tiny red cow-udders of cowbag clover (sometimes called poverty clover). I've never observed pollinators visit this diminutive one inch plant, but they delight me nonetheless.
Lithophragma aff. parviflorum
Woodland stars, Lithophragma spp., are small scented flowers in the Saxifragaceae. They are pollinated primarily by invariably dull Greya moths. The moths are usually grey or white, and quite slender.
Olsynium douglasii
Grass widows, Olsynium douglasii, are relatively large beautiful flowers in the Iridaceae (related to Iris, Crocus, Crocosmia, and others). They are often the first blooms found on the top of Upper Table Rock, growing up to twelve inches. Oddly, I've never witnessed bees visiting the flowers despite seeming very attractive. Large bees like bumble bee queens are probably important pollinators for grass widows. An interesting feature of O. douglasii is that nectar is excreted directly from the filaments (stamens). (See Rudall et al. 2003)
Limnanthes aff. floccosa
Meadowfoam, the source of one of my favorite varietal honey, was here and there on the Upper Table Rock summit.
Chickweed monkeyflower (Erythranthe alsinoides)
Monkeyflower likes growing where seeps or springs keep the soil wet. I don't often see bees visit these plants, but they're popular with mason bees (Osmia spp.) where I've surveyed for bees.
Vernal pool
One of the features of both Table Rocks are the many vernal pools, home to tiny freshwater fairy shrimp (Branchinecta lynchi). By summer, the pools are completely dry. The miraculous lifecycles of the minuscule shrimp contend with this by going into a type of dormancy. Mosses and various plants like to grow on the margins of these pools allowing bees and other insects to safely land and drink.
Garter snake (Thamnophis sirtalis)
The vernal pools are hotspots for a variety of wildlife. I was surprised to find a garter snake hidden in the marshy grasses!
Burrow entrance of mountain pocket gopher (Thomomys monticola)
Undoubtedly, garter snakes and other predators hunt the various vermin that call the Table Rocks home. Gophers serve an important role on the mesa, tilling the soil and creating perfect soil beds for seeds to germinate. Many native plant seeds need direct soil contact as well as sunlight to germinate.
Dog tick (Dermacentor variabilis) ♂
With vertebrates come parasites. Ticks are an unfortunate risk when hiking, and it's important to be on the lookout. You can reduce your risk of picking up a tick by staying on the trail and thoroughly checking your clothes and body before you get in your car and when you get home. Ticks are like tanks and can survive for days or even weeks without food or water, even in extreme heat. I once kept a tick in a sealed jar on my dashboard in summer, the thing survived for a week!
Sayfly (Tenthredinidae)
Sawflies are related to bees and wasps, are are probably most similar to the ancestral predecessors of all Hymenoptera. Most sawflies feed on plant material, but adults occasionally feed on carbohydrate-rich nectar.
A view of Mount McLoughlin midway up the Upper Table Rock trail
Upper Table Rock trail is not very long or difficult, but it's worth taking your time to view the surrounding infrastructure surrounding the Table Rocks. Farms and ranches contrast with the nearly pristine landscapes flanking the trail. It's a bit sad.
White leaf manzanita (Arctostaphylos viscida) and honey bee
Manzanita bloom was starting to peak at the time of my hike. The highest diversity of bees could be found on these large shrubs. Honey bees might not be the best equipped to pollinate the flowers or reach the nectar due to the constricted urn-shaped flowers. Poricidal anthers keep pollen restricted only to bees that can sonicate, or buzz pollinate, the flowers. Sonication is when the bee grabs onto the flower and vibrates the flight muscles, a feat honey bees haven't evolved to do.
Habropoda depressa 
Mountain digger bees, Habropoda depressa, can and do sonicate flowers. White-leaf manzanita are commonly visited by the bumblebee-sized digger bees.
Nomada aff. erigeronis
Nomad cuckoo bees (Nomada spp.) are beautiful red kleptoparasites of Andrena and other solitary bees. They are in the Apidae which encompasses honey bees (Apis spp.), bumble bees (Bombus spp.), digger bees (Anthophora and Habropoda spp.) and others. Males patrol host nest sites and mimic the odors of the host species, which are deposited on the females during mating. This allows female Nomada to enter host nests without being detected. These fascinating wasp-like bees always make my heart skip a beat. They are so awesome! Not awesome for the host bees, since the cuckoo bee larvae kill the host larvae with large sickle-shaped mandibles, then proceeding to feed on the pollen provisions provided by the host mother.
A potential host for the cuckoo bees, mining bees are quite fond of manzanita blooms and are probably the most numerous bee types on the shrubs at any given time. They probably visit the flowers primarily for nectar, and not so much for pollen.
Mining bees can't access the tight manzanita flower entrances to reach the nectar, so they are often seen biting holes in the sides of the flowers to rob the nectar. This is very disadvantageous for the plants, but allows the short-tongued bees to feed. Other bees may find the holes in the flowers and exploit them by enlarging them.
Beefly (Bombyliidae)
A variety of other pollinators are attracted to the abundant manzanita blooms. Beeflies are convincing bee mimics which look like flies puffballs with stick legs. They are mostly parasitoids of ground nesting bees (often Andrena and Halictus). Instead of crawling into the nests of their hosts, they hover over the ground and, with a thrust of their butts, jettison their eggs directly into the entrance of their hosts' nests.
Hummingbirds are also quite fond of the small flowers! Each individual flower probably produces miniscule quantities of nectar for the relatively large floral visitors, but manzanitas make up for it by producing hundreds of thousands of flowers per shrub.
Thrips (Orothrips sp.)
Often viewed as pest insects, thrips are likely to be very important to hummingbirds. I have suspected for many years that hummingbirds are seeking thrips along with the nectar when visiting manzanitas.
Garrya fremontii
Silktassel is one of those shrubs that I've walked past a hundred times before noticing it, but it was quite beautiful in bloom. Garrya is dioecious, having both male and female plants. The one photographed above was a male, offering only pollen. Silktassel is wind-pollinated, which makes sense considering I observed zero pollinators of any kind anywhere near it.
Garrya fremontii flowers
Bees may visit Garrya if nothing else were available, but it is likely the pollen is deficient in nutrients and protein. There are many bees that collect wind-pollinated pollen, even some specialists.
Here is a view of the unnerving dichotomy between Upper Table Rock and the surrounding landscape. There was a time, long before I was born, when everywhere was as serene and beautiful as Upper Table Rock. Humans have a superiority complex.
Children had left touching and important messages for the hikers. Treat wildlife very nice. The message everyone needs to hear. Take heed!