Lars Fröberg

Differential herbivore damage to calcicolous lichens by snails

Abstract Abstract: A laboratory experiment was conducted to determine the damage caused by snail grazing to 35 calcicolous lichen species and cyanobacteria from the Baltic island of Oland, Sweden. Individuals of four species of land snails ( Balea perversa, Chondrina clienta, Clausilia bidentata and Helicigona lapicida ) were allowed to graze on identified lichen species growing on pieces of limestone. Snail grazing on thalli and ascocarps was classified into four categories ranging from no damage to completely eaten. In general, some lichen species were heavily grazed, whereas others were only slightly damaged or not injured. Aspicilia calcarea, Tephromela atra and Verrucaria nigrescens were preferred by all snail species except Chondrina clienta . In general, lichen thalli that were not immersed in the calcareous rock and cyanobacteria were preferred, whereas ascocarps were avoided by one of the snail species ( C. clienta ). Immersed perithecia with a carbonized outer layer were avoided by all snail species except C. bidentata . Possibilities of chemical and mechanical defence properties in calcicolous lichens are discussed.

Herbivory on calcicolous lichens: different food preferences and growth rates in two co-existing land snails

A total of 32 calcicolous lichen species, one alga and one bryophyte were recorded on a limestone wall in the grassland Great Alvar on the Baltic island of Öland, Sweden. Fourteen (41%) of these 34 species and free-living cyanobacteria showed herbivore damage, most probably due to grazing by the land snails Chondrina clienta and Balea perversa which inhabited the limestone wall. Three laboratory experiments were conducted to examine the food preferences of individuals of C. clienta and B. perversa collected at this site and to evaluate any association between their preference and the net food quality of the lichens to the snails. Chondrina clienta and B. perversa exhibited food preferences, which differed significantly between species. Within species, variation in food choice was similar among individuals. This indicates that snail populations may be composed of polyphagous individuals with similar food preferences. Different lichen species were of different net food quality to the snails as indicated by growth rate differences. In both snail species the most preferred lichen species of the choice experiment caused the largest weight increase in juveniles, viz. Caloplaca flavovirescens for C. clienta and Aspicilia calcarea for B. perversa. This suggest that the snail species studied differ in their abilities to deal with secondary compounds and physical characteristics of certain lichens or that they can utilize the energy and nutrients of these lichens to a different extent. It is suggested that differential food preferences might reduce the intensity of interspecific competition for resources (lichens) between C. clienta and B. perversa.

Chemical variation within and between individuals of the lichenized ascomycete Tephromela atra

Abstract HPLC-analysis was used to determine the concentrations of the lichen compounds alectoronic acid (depsidon), α-collatolic acid (depsidon) and atranorin (depsid) in the lichenized ascomycete Tephromela atra (syn. Lecanon atra ) (Hudson) Hafeliner from limestone walls on the Baltic island of Oland, Sweden. In 24 individuals of T. atra sampled on a stone wall, the pre-reproductive and reproductive tissue did not differ in the concentrations of alectoronic acid, collatolic acid and atranorin. The concentrations of the three lichen compounds were inter-correlated in the reproductive tissue, but not in the pre-reproductive tissue. Single individuals of T. atra ranged in area covered from 10.1 to 147.4 cm 2 (mean: 38.5 cm 2 ; N =24); 38.6% of this area was pre-reproductive tissue. However, the concentrations of the three lichen compounds were correlated neither with the total area covered by the lichen nor with the percentage of pre-reproductive tissue. This suggests that the concentrations of the lichen compounds do not change with increasing size (age) of the lichen. Analysis of specimens of T. atra from eight localities revealed a significant variation in lichen compounds (range between localities: alectoronic acid 0.60–3.26 μg/mg lichen dry weight (DW); collatolic acid 2.14–11.59 μg/mg lichen DW; atranorin 0.58–4.16 μg/mg lichen DW). The level of grazing observed in the lichens differed significantly among localities. However, no correlations between the concentrations of the three lichen compounds and the grazing damage to the lichens were found.

Snail herbivory decreases cyanobacterial abundance and lichen diversity along cracks of limestone pavements

Herbivores are known to decrease plant species diversity in ecosystems with low productivity. Limestone pavements are low-productive habitats harboring specialized communities of cyanobacteria, and endo- and epilithic lichens exposed to extreme temperature and humidity fluctuations. Pavements of the Great Alvar (O¨ land, Sweden) are covered by free-living cyanobacteria giving the rock surface a dark color. Based on cyanobacterial abundance along the edges, two types of cracks intersecting the pavements have been described: Type one with abundant cyanobacteria and type two without cyanobacteria resulting in light-colored edges. Erosion and different lengths of inundation by melt water have been suggested to cause the conspicuous differences in community composition and hence color between cracks. We hypothesized that this pattern results from the grazing activity of the cyanobacteria- and lichen-feeding snail Chondrina clienta, which reduces cyanobacterial cover along light-colored cracks and facilitates endolithic lichens. Three dark and three light-colored cracks were investigated at each of three localities. Crack characteristics (i.e., aspect, width, depth and erosion) and snail density were assessed at the crack level. Cyanobacterial cover and lichen diversity were recorded in 1-cm sections, sampled every 5 cm along eight 160-cm-long transects per crack. Model selection was applied to estimate effects of snail density and distance from crack edges on cyanobacterial abundance and lichen diversity. Crack characteristics explained no differences in cyanobacterial cover or lichen diversity. However, cyanobacterial cover decreased towards the edges of cracks with high snail densities. A transplant experiment supported the correlational evidence. The abundant cyanobacterial cover on pieces of stone placed close to cracks with high snail densities was completely grazed within 19 months. By contrast, cyanobacteria recolonized initially completely grazed pieces of stone when fixed near cracks without snails. Abundance and diversity of endolithic lichens increased along cracks with high compared to low snail densities but decreased in epilithic lichens and lichens with cyanobacterial symbionts. However, the presence of the gastropod herbivore decreased overall lichen diversity. Comparing presence-absence matrices with null models revealed that species co-occurred less frequently than expected. Taken together, we provide evidence that herbivory indirectly released endolithic lichens from competition for light by reducing cyanobacterial cover. (Less)

Effect of rock climbing on the calcicolous lichen community of limestone cliffs in the northern Swiss Jura Mountains

Exposed limestone cliffs in the Swiss Jura Mountains harbour a diverse lichen community with some rare species. Sport climbing has recently increased in popularity on these cliffs. We examined the effect of sport climbing on calcicolous lichens by assessing species diversity and cover of lichens in climbed and unclimbed areas of 10 isolated cliffs in the northern Swiss Jura Mountains. We also investigated possible associations between lichens and lichen-feeding land snails on these cliffs. A total of 38 calcicolous lichen species, three bryophytes and one alga were found on the rock faces of 10 cliffs. Twenty lichen species (52.6%) were epilithic, 16(42.1%) endolithic and two (5.3%) foliose. Overall, the epilithic lichen species covered 8.3% of the rock surface, endolithic species 10.2%, and foliose species 0.03%. Climbed and unclimbed rock areas did not differ in total number of lichen species, species density (number of species per 100 cm(2)) or total lichen cover. However, the frequency of occurrence of epilithic lichens was lower along climbing routes than in unclimbed areas. A multi-response permutation test showed that the lichen community composition of climbed areas differed from that of unclimbed areas. The dissimilarity of lichen communities between climbed and unclimbed areas increased with increasing climbing intensity on the focal route in climbed areas, but not with the age of the climbing route. Five of the 11 snail species recorded on the cliff faces were specialized lichen feeders. Plots along climbing routes harboured fewer snail species than plots in unclimbed areas. Total snail abundance was positively correlated with lichen species richness, but no correlation between snail species richness and lichen species richness was found. Our results indicate that frequent rock climbing can change the lichen community and reduce the snail community of limestone cliffs. A climbing-related reduction of snail abundance may also alter the lichen-herbivore interaction and indirectly change competitive interactions among lichen species. (Less)

Field study on the regenerative capacity of three calcicolous lichen species damaged by snail grazing

Lichen growth and regeneration depend on the net photosynthetic production, the lateral allocation of products, on abiotic factors, competition and herbivory, and may therefore vary both in space and time (Hill 1981). Herbivores cause different damage to lichens in response to different thallus structure (surface toughness) and growth form, presence/absence of secondary compounds, and due to herbivore-specific differences in feeding (Lawrey 1984; Froberg et al . 1993; Baur et al . 1994; Hesbacher et al . 1995). Regeneration of artificially damaged lichen tissue has been investigated in detail, for example in Xanthoria parietina (L.) Th. Fr. (Honegger 1996; Honegger et al . 1996). However, quantitative assessments of the regenerative capacity of thalli damaged by herbivores are so far lacking. Damage to lichens by grazing gastropods is made by highly specialized radulae and can therefore not be imitated by any mechanical treatment (Baur et al . 2000). Herbivory by snails also involves the production of saliva and mucus, which both could affect lichen regeneration.

Age and epiphytic lichen diversity of the dwarf shrub Helianthemum oelandicum on the island of Öland, Sweden

Lichen cover and diversity were analysed on the dwarf shrub Helianthemum oelandicum (L.) Dum.Cours. at one site in the calcareous grassland of the area known as the ‘Great Alvar’ on the Island of Oland, Sweden. The age of 22 phorophytes was determined by ring counting and varied from 8 to 41 years and was accurately predicted by the root diameter. A total of 18 lichen species was found, with a range between 0 and 13 species per phorophyte. The number of lichen species on living H. oelandicum were correlated with the phorophyte age. The number of lichen species and their coverage were greater on dead compared with living phorophytes. The species number was also higher on thin branches compared with thick branches and roots and some of the species showed preferences for dead phorophytes, and for thin branches. This study of lichen colonization and growth on dwarf shrubs in relation to phorophyte age is a new application of herbchronology. (Less)

Professor Ingvar Kärnefelt - a birthday tribute

On 19 July 2009 Ingvar Karnefelt celebrated his 65th birthday. This could have meant that we, his former students, would be celebrating him in his retirement from his position as head of the Biolog ...