By Laurel Martinez (University of Vermont)
Every Round River student partakes in writing “Grinnell journals” to document their observations in the natural world, as part of our Natural History and Field Methods courses. The Grinnell System was initiated by Joseph Grinnell at the University of California at Berkeley, Museum of Vertebrate Zoology. Grinnell (1877-1939), an accomplished zoologist, was an authority of both birds and mammals of the western United States. The Grinnell System Naturalist’s Field Journal is a systematic approach using writing, drawing and observation skills to examine biotic organisms.
The following in an Grinnell entry from Laurel Martinez, a student currently on the Round River Botswana, who writes about her observations around camp that are more of the microscopic variety, compared to the large, charismatic megafauna that is normally associated with Africa.
Mangosteen leaf drawing from the Grinnell entry.
Date: February 27, 2016
Locality: “HQ campsite,” NG34, Sankuyo concession, Botswana
Route: Mangosteen tree on the right side of the camp facing the watering hole. Adjacent to swimming pool remains. Mode of transport – foot.
Time: Observations span 14:40-15:40
Weather: 30 C, partly cloudy (2/4), wind = 5 on Beaufort scale, app. North, no precipitation
Habitat: Underneath Gardenia volkensii (Mangosteen) tree in area shaded by its canopy. Mostly bare disturbed ground with a few Poaceae spp. and a small Malvaceae spp.
General Commentary: I spent an hour making observation of the micro-ecosytem underneath a large (~30ft) Gardenia volkensii. The tree itself has large ovate leaves of a dark green color. The margin of the leaves are entire and they are simple. Mangosteen trees have a whorled branching pattern which the leaf position also follows. The leaves are also thicker and more leathery which is useful in identification. This tree in particular has two main branches/trunks, which split off very low to the ground. Perhaps these are two different trees growing next to one another. The bark of the tree is mainly a dark green-brown color with cracked fissure patterns, almost like dried clay. In some areas the bark is a yellowy rusted color, especially towards the base of the tree. I think this may be some kind of lichen or fungus. The cracked fissures in the bark of the tree appear to be more pronounced toward the top rather than the finer and shallower grooves toward the bottom. Unfortunately the tree is not in flower although according to Vincent Carruthers, authors of “The Wildlife of Southern Africa” the flowers are large and white, turning yellow as they age and producing a melon-liked ridged fruit. Its season is July – October.
One aspect of the mangosteen tree that drew me to observe it is the large gashes raking the side of the trunk. These gashes were made from Loxodonta africana, the African elephant. This behavior may be to scratch an itch or, because elephants are highly emotional and complex animals, the behavior may be a vent of frustration or response to stress. A member of the subfamily Apinae (honeybee) frequents the gashes in the tree, drawn to the opaque orange sap that is likely sugary. The species found in this region is Apes mellifera. I also noticed small black ants frequenting the gashes to collect sap. Because of their dark color and long legs, I believe these ants are in the Formicidae family. They formed relatively straight lines in the tree, although their abundance was low.
The mangosteen tree was staked by the nails and screws, the most obvious near the base of the tree. There used to be a research camp nearby which may be why the nails and screws are in the tree. I am curious about the ecological effects of the remains of the research camp. We may see signs of ecological succession in response to this human disturbance.
At 14:51 a Streptopelia capicola, Cape turtle dove, lands in the tree. It uses short back wingbeats to slow its momentum and lands feet first to perch on a branch. The Cape turtle dove then folds its wings and rests for a few minutes before taking off and landing in another tree out of sight. Several other birds call from the surrounding mangosteen trees including Streptopliea semitorquata (red-eyed dove) and Lanianus atrococcineus (crimson-breasted shrike), among others.
A colony of ants in the Formicidea family (Matabele ants) reside underneath this tree. I noticed five of the matabele ants crawling in the area under the three. They appear to travel more randomly than the Formicidae ants, which form regimented lines. I watched one ant for several minutes, and every 2-3 minutes it would stop, wave its antennae, and change direction. I assume this is in response to a chemical signal for directions of food. One ant carries a grain of rice, it struggles to climb over and under the crushed yellow grass.
I followed the ant with the rice until it reached the hole. I pushed aside some grass to reveal the entrance to the colony. Five more ants gathered around the hole, one trying to pull a large piece of onion down. It didn’t fit well, and the ant with the rice pushed aside the onion after a few minutes and brought the rice down. It had huge mandibles which it used to easily move aside the large onion. The ants may have chosen this location for the shade the mangosteen offers, or perhaps the protection of the grass. Human settlement nearby may have also been a deciding factor as we provide lots food.
The honeybee has returned to the mangosteen again, this time staying for a longer period of time. It circules around me, the low buzz of its wings contrasts with the higher pitch of surrounding flies. The bee lands on the gashes in the tree again, darting methodically in horizontal transects across the exposed inner bark. It works back and forth, never landing in one spot for too long. After a few minutes, it takes off for good, presumably returning to the hive. It may belong to the hive in a Kigelia africana (sausage tree) we found earlier in the week.
The lower branches of the mangosteen appear to have sustained some damage. They are broken and defoliated which I believe is due to elephant browsing. While I do not know if elephants are known to feed on mangosteen, their large size and consequential energy needs would lead me to say yes. Some of the damage also appears to be caused by humans. There are missing branches that have a smooth surface, indicating that they have been cut.
Leaves from the mangosteen litter the ground below, likely from the recent rainstorm. By now, they are all dry and crunchy, and brownish rather than the dark green of living leaves. One leaf appears to have been eaten by some kind of insect. The edges of the leaf are darker and flakey dead tissue. A track of this dead tissue leads to a larger patch of damage toward the midrib of the leaf.
The microecoystem beneath the mangosteen offers a glimpse into the larger systems at work in the natural world. By studying and observing the smallest organisms below our feet, we can gain insights into the rich complexity of life on earth.