Plants and Ants: Echium, Oat, Barley, Bromus, and Wild Wheat
Some 20 years ago, the foothills of the Samarian Desert, between the memorial to fallen soldiers in the Jordan Valley and the settlement Yaffit were dotted with nests of harvesting ants. When climbing one of the hills near the main highway of the Rift Valley, we discovered that one of the most common and prominent plants is Echium judaeum (Figs. 8.7.1-8.7.3). Additional study of the Echium nutlets shows that they have no elaiosome (Fig. 8.7.4 right). The fruit of plants from the Boraginaceae is mostly a nutlet with a very hard coat; many species have an oily body at their base. Unlike the other species mentioned here, E. judaeum is not a ruderal plant. It seems reasonable to assume that the Echium nutlets tempt the ants by their scent, but because of difficulty breaking the hard nutlet coat, they transfer the mericarps, each with one seed, to the threshing zone where they germinate and develop well (Figs. 8.7.2-8.7.3).
8. Oat, Barley, Bromus, and Wild Wheat
We started on our way following in the ants’ paths with cultivated annual grasses domesticated by humans from the reservoir of wild plants of the East Mediterranean area during the last 10,000 years. These were patches of wheat and barley well developed near nests of harvesting ants in fields of the northern Negev. The wild plants which were domesticated are Hordeum spontaneum – the progenitor of the cultivated barley, and Triticum dicoccoides – the progenitor of the wheat. The latter is known in Hebrew as “The Wheat Mother”. The response of Hordeum spontaneum, Triticum dicoccoides, and other annual grasses to ant activity is clearly prominent in Figs. 8.7.5-8.7.10. Ant nests crowned with wild barley (Figs. 8.7.7/1 and 8.7.8) become prominent when the wind moves the spikes which are almost horizontal. Avena sterilis (Fig. 8.7.7/2) is prominent near ant nests as compared to the non-blooming specimens surrounding it. The plants of Avena sterilis that developed at the colored Anemone coronaria reserve in Esdraelon Plain are prominent and function as an interesting point for evaluating the function of the nest in the landscape. The deep clayey soil of that area is regarded as fertile, but the large and dark green A. sterilis plants developing there (Fig. 8.7.9), prove that there is a nutrition limitation in that area. It is possible that the nest ameliorates the aeration of the clayey soil. The rhizosphere, which contains much water during the winter, may have oxygen deficiency that acts as a limiting factor to plant development.
A field that was cultivated and abandoned in a terrace near Kiryat Menachem had a dark-green spot that did not look like a patch of barley or oat (Fig. 8.7.10). Checking the plants revealed a young (and hence hard to determine) annual Bromus. At the left half of Fig. 8.7.10 there is a small, light-green specimen and a dark-green specimen from near the nest. This finding implies that there are more plants that are related to ants’ activity and opens the way for further investigation. Among these plants I could list Sinapis alba and Hirschfeldia incana as having prominent inflorescences. I anticipate the finding of additional species that are ant-related but have a more “modest” appearance.
For further reading:
- Danin, A. 1989. Nests of harvesting ants – a primary habitat of a few synanthropic plants in Israel. In: E. Spanier, Y. Steinberger & M. Luria (eds.) Environmental Quality and Ecosystem Stability: Vol. V-B: 449-457. ISEEQS Publication, Jerusalem.
- Danin, A. 1989. Nests of harvesting ants: a preferred primary habitat of wild Beta vulgaris in Israel. In: K. Tan (ed.) The Davis & Hedge Festschrift: Plant taxonomy, phytogeography, and related subjects. pp. 223-232. Edinburgh University Press.
- Danin, A. and Yom-Tov, Y. 1990. Nests of harvesting ants as primary habitats of Silybum marianum L. Pl. Syst. Evol. 169: 209-217.