Ecology

Lichens, vertebrates and invertebrates

A large number of invertebrate or vertebrate species use lichens in various ways and this page will give some examples. Humans, though vertebrates, will be ignored here since there is a separate HUMANS AND LICHENS page.

Amongst the non-human vertebrates the reindeer and caribou are possibly the best known users of lichens. Those animals eat terrestrial or arboreal lichens, especially during the winter months when lichens are the major food source for reindeer and caribou and they will dig through the snow to reach the lichens. Each animal may eat 3 to 5 kilograms of lichen per day during winter but lichens are low in protein and though they allow the animals to survive the winter months the animals lose weight. Lichens are also generally poor in various minerals so the reindeer and caribou may also show symptoms of mineral deficiency by the end of winter. Reindeer and caribou have been found to eat lichens within these genera: Alectoria, Bryoria, Cetraria, Cladina, Evernia, Flavocetraria, Hypogymnia, Stereocaulon, Umbilicaria and Usnea. Experiments in which reindeer were tested for winter food preferences showed Cladina and Bryoria to rank high, ahead of two dwarf shrub species, a grass and a moss that were also offered during the trial. The experimenters proposed that, during winter, reindeer might get most of their protein from vascular plants but that lichens could satisfy much of the reindeer energy requirements. Several North American and Eurasian deer species have also been seen eating lichens as have goats, musk oxen, lemmings, voles, marmots, squirrels, camels, llamas and guanacos. In some of these cases there is insufficient evidence to determine whether lichen eating is a regular or sporadic activity. In the Jiddat al Harasis area of central Oman gazelles (Gazelle gazelle arabica) are known to eat the fruticose species Ramalina duriaei, which is often soft and palatable in the mornings because heavy dews are common through much of the year. The lichen is low in protein but has an appreciable digestible carbohydrate content and produces bourgeanic acid, a fatty acid. It is possible that (as suggested also for reindeer) lichens could make a significant contribution to gazelle energy needs, though only a small contribution to protein requirements.

Many bird species from Eurasia, the Americas and Australasia are known to use lichen fragments in their nests, most likely for camouflage. To give one situation as an example, consider a small bird that builds its twig nest in the dappled light found within many shrubs. In such a setting a nest built just of twigs would be discernible as an eye-catching dark mass in an otherwise dappled setting and could arouse a predator's curiosity. Fragments of lighter-coloured lichen thalli, affixed to the outside of the nest, would give it a dappled look, better able to blend with the dappled light. This webpage [LINK] gives more details about the use of lichens by North American wildlife.

Christmas Island in the Indian Ocean is well-known for its red crabs (Gecarcoidea natalis) and their spectacular annual migration. During field work on the island in the year 2000 the Australian lichenologist Patrick McCarthy observed a mature crab eating the lichen Ramalina dumeticola. The crab removed a tuft of this fruticose species from a fallen branch, held the lichen in one claw and a leaf in the other and, for several minutes, delicately ate one and then the other.

Numerous other invertebrates make varied uses of lichens and the two sources given in the next reference button give much information about lichen-invertebrate associations. You can also find an overview of lichen-invertebrate associations (as well as a long list of references) on this webpage [LINK].

Lichens are eaten by many small invertebrates, including species of bristletails (Thysanura), springtails (Collembola), termites (Isoptera), psocids or barklice (Psocoptera), grasshoppers (Orthoptera), snails and slugs (Mollusca), web-spinners (Embioptera), butterflies and moths (Lepidoptera) and mites (Acari). The mite Camisia segnis lays eggs in lichens and during egg laying a softening substance is excreted by the female and this causes the lichen to swell, grow over the eggs and so protect them. After hatching the larvae feed on the lichen thallus. South-east Asian termites in the genus Hospitalitermes graze on lichens, though not necessarily exclusively so in all species. The termites forage mainly in canopy lichens and foraging trails may extend several tens of metres. Lichen scrapings are gathered into small balls which are carried back to the nest. The lichens presumably provide a source of nitrogen since analysis of the lichen balls showed them to have nitrogen contents from 10 to 60 times greater than that of wood. The AUSTRALIAN MOTHS CASE STUDY gives some information about moth larvae that eat lichens.

Invertebrates may be choosy eaters, some having preferences for certain species or for certain parts. The intertidal isopod Campecopea hirsuta feeds on Lichina pygmaea but only on the algal cells. A study of two lichen-eating psocid species on larch trees in England showed that while both species ate Lecanora conizaeoides, one species grazed indiscriminately but the other grazed only on the apothecia. Web-spinners are tropical to sub-tropical insects that build tubular, silken galleries in which they live. They are constantly expanding these galleries in search of new food sources and the galleries can develop into quite intricate maze-like forms. In Australia lichens are the preferred food for species of the web-spinner genus Notoligotoma. A study of Notoligotoma hardyi from Magnetic Island in Queensland showed that members of this species mostly built their galleries across lichen colonies growing on rocks and rarely on lichens growing on tree bark. The rocks hosted a variety of lichen species but the Notoligotoma hardyi galleries were not randomly distributed across the rocks. Statistical analysis that took into account such factors as variation in lichen colony sizes indicated that Notoligotoma hardyi had a strong preference for Buellia substellulans. The gallery coverage of that lichen species was over twice the area expected from just random choice alone.

A variety of invertebrates shelter within lichen colonies that grow on rocks, bark or on the ground. Many other invertebrates are coloured in ways which allow them to be inconspicuous when they come to rest on lichen colonies. Various invertebrates carry lichen fragments as camouflage and some examples are given in the Australian moths case study referred to above. In addition some lacewing larvae cover themselves with moss or lichen fragments which, at least in some cases, helps these predatory invertebrates take their prey by surprise. Perhaps the most striking examples of camouflage are provided by Papua New Guinean weevils in the genus Gymnopholus. Lichens have been found on at least ten Gymnopholus species, including the aptly named Gymnopholus lichenifer, the second half of its scientific name meaning 'lichen bearer'. The weevils support micro-gardens of algae, fungi, bryophytes or lichens and, in turn, the gardens support a variety of micro-invertebrates.