Carnivorous mammals as seed dispersers of Myrtus communis (Myrtaceae) in the Mediterranean shrublands

ABSTRACT

The role of carnivorous mammals as seed dispersers of Myrtus communis L. in the Mediterranean environment was studied. Seeds of M. communis were found in faeces of red fox (Vulpes vulpes L.) and carnivores from the genus Martes, at four sites on the Tyrrhenic coast of Southern Italy in the period autumn-winter 1993–1995. All the study sites are covered by Mediterranean shrublands with M. communis as one of the dominant species. Content analysis of fox scats showed that fruits of M. communis constitute a relevant component of the diet of these carnivores, although other food categories were also well represented. Further investigations on the effect of mammal digestion on seed germinability showed that carnivores not only moved the seeds away from the mother plant but also enhanced their germinability. This species was known to be bird- and ant-dispersed and the adaptive implications of a multi-vectorial seed dispersal process is discussed.     

Observational evidence that diversity may increase productivity in Mediterranean shrublands

This paper reports field observational evidence on the diversity-biomass production relationship from eastern Mediterranean shrublands dominated by Cistus salviifolius. The main results are: (1) plant diversity and ecosystem primary production are positively correlated in the Cistus shrublands, which are multigrowth form systems; (2) the taxonomic and growth form diversity in Cistus shrublands suggests that there is strong differentiation along the structural niche axis, and thus functional redundancy is weak; (3) the performance of the dominant Cistus in terms of biomass production did not affect the overall diversity-biomass production of the studied communities. Received: 18 October 1999 / Accepted: 13 April 2000     

Critical stages in the recruitment process of Rhamnus alaternus L

BACKGROUND AND AIMS: Rhamnus alaternus is a Mediterranean shrub commonly used in reforestation programs. Although several aspects of its reproductive biology have been studied, little is known about the importance of the different recruitment stages in the overall regeneration process of this species, which limits its proper use in Mediterranean forests and shrubland management. The aim of the present work was to quantify the importance of the different recruitment stages in the regeneration process of R. alaternus. METHODS: Two populations of Rhamnus alaternus on the island of Mallorca that differ in climatic conditions, type of habitat and sex ratio were studied. The importance of seed production, seed dispersal and predation, seedling emergence and seedling survival for the regeneration of this species were quantified. KEY RESULTS: In both populations, fruit set and fruit removal by animals were not critical stages, since almost half of the flowers became mature fruits and 90% of those were dispersed. Most seeds were deposited under female conspecifics (86 and 47%, at Lloret and Esporles, respectively), and very few were found in open inter-spaces (1 and 5%). Post-dispersal seed predation (mostly by ants and rodents) was very high in both populations. Seedling emergence took place during autumn and early winter and it ranged from 31 to 68% depending upon year and microhabitat. The majority of emerged seedlings died during the first year, mainly due to desiccation; such mortality was influenced by rainfall and differed among microhabitats (varying from 67 to 100%). The general spatial distribution of seed rain was concordant with the seedling emergence and survival pattern in both populations. CONCLUSIONS: The recruitment of Rhamnus alaternus appeared to be mainly limited by seed and seedling survival, regardless of the type of habitat in which the species is found.     

Types of pollination and seed dispersal in Mediterranean plants

Abstract

Selected examples of pollen and seed dispersal in Mediterranean plants are described. The aspects of pollination considered are: comparison between cleistogamous and chasmogamous forms in the same species; differences in attractants and rewards; duration of pollen viability according to pollination syndrome. The aspects of seed dispersal considered are: presence or absence of specialized structures for dispersal; examples of active, passive and induced dispersal; animals involved in seed dispersal and their reward; type and functions of elaiosomes.     

The mycorrhizal status of the woody Mediterranean shrub Myrtus communis L.

  Myrtus communis L. (myrtle), a typical Mediterranean plant species belonging to the family Myrtaceae, was shown to form arbuscular mycorrhizal symbioses in nature. Many different spore types were isolated from its rhizosphere and grown in pot cultures; six of them were identified as Glomus species. In the laboratory, the myrtle root system was colonized by indigenous endophytes as well as by an Italian isolate of Glomus intraradices. In greenhouse experiments, mycorrhizal inoculation reduced transplant stress in 60-day-old myrtle seedlings; their growth was renewed immediately after transplanting, whereas non-mycorrhizal plants stopped development. Significantly larger growth responses were obtained using indigenous fungi than the Italian isolate of Glomus intraradices. Accepted: 16 January 1997     

Myrmecochory in Australia's seasonal tropics: Effects of disturbance on distance dispersal

Abstract Successful ecosystem restoration requires the re-establishment of fundamental ecological processes, many of which involve plant-animal interactions. Myrmecochory (seed dispersal by ants) is a particularly important plant-animal mutualism in Australia, but little is known about its response to either disturbance or restoration following disturbance. Here we investigate the effects of disturbance on seed dispersal by ants, and the extent to which the ant-seed relationship has re-established at sites undergoing rehabilitation, at Ranger uranium mine in the seasonal tropics of Australia's Northern Territory. We focused on the composition of seed-dispersing ant assemblages, rates of seed removal by ants, and the dispersal curves generated by ants, as determined by observations of removal from seed depots. Ten sites were studied, comprising four ‘natural’ (undisturbed) sites representing a range of savanna habitats occurring in the region, four disturbed sites representing a range of habitat disturbance but with intact soil, and two waste rock sites subject to preliminary revegetation trials. A total of 22 ant species from 10 genera were observed during 154 observations of seed removal, most commonly Rhytidoponera aurata (53 records), Monomorium (rothsteini gp) sp. 1 (14), Iridomyrmex sanguineus (13), Iridomyrmex pallidus (12) and Pleidole sp. 3 (10). Removal rates (over 3 h) averaged 29% across all sites and time periods, varying markedly both between and within sites. However, mean rates of removal were similar between natural, disturbed and waste rock sites (29%, 28% and 31%, respectively). A high incidence (62% of all depots) of'aril robbing’ by ants (primarily Monomorium spp.) eating arils in situ, without removal, was observed. Dispersal distances varied markedly between ant species, with Iridomyrmex sanguineus having both the highest mean (7.25m) and maximum (13.08 m) dispersal distances. Species of Pheidole typically dispersed seeds less than 0.5 m, and Meranoplus, Monomorium and Tetramorium spp. only ever moved seeds a few centimetres, usually dropping and abandoning them before reaching the nests. The dispersal curves characteristic of each site varied markedly due to the different composition of seed-dispersing ants. The mean dispersal distance at disturbed sites (3.91 m) was significantly higher than at natural sites (2.19 m), and the curves were strongly skewed in the former, but relatively uniform in the latter. The implications of these differences for recovery following disturbance are unclear. At rehabilitated waste rock sites, all observed removals involved distances less than 0.5 m, with a mean of 17 cm. This lack of effective ant-seed relationships might represent a barrier to further vegetation development at rehabilitated sites.     

Satiation in Collection of Myrmecochorous Diaspores by Colonies of <Emphasis Type="Italic">Aphaenogaster rudis</Emphasis> (Formicidae: Myrmicinae) in Central Ohio,USA

When ants are dispersing seeds (myrmecochory), cessation of foraging can be as important as recruitment in determining dispersal success. We studied food collection by Aphaenogaster rudis from experimental depots by monitoring temporal variation and preference in food removal (diaspores of Asarum canadense and Sanguinaria canadensis and larvae of Tenebrio obscurus). Removal of diaspores, but not insect larvae, declined to nearly zero over the scale of hours. Satiation extended over the scale of days for diaspores. Extensive collection of larvae inhibited future collection of diaspores, but the converse was not observed. Increasing distance from the nest reduced removal of diaspores, but not of food bodies isolated from diaspores. Removal rates for diaspores were uncorrelated with the number of workers or brood in a colony.     

Pollination biology and sexual differentiation ofOsyris alba (Santalaceae) in the Mediterranean region

Osyris alba L. is a widespread dioecious hemiparasitic shrub of S Europe, N Africa, and SW Asia. Male inflorescences are multiflowered whereas each female inflorescence is reduced to a single flower with persistent enlarged bracts. Pollination is a prerequisite for fruit and seed development and wind is unlikely to be an effective means of pollen spread. In southern Italy pollen is transported by small unspecialized flies and beetles. Both male and female flowers produce an indistinguishable sweet odour. Male flowers are produced in large numbers and over a larger period than the females and provide pollen, nectar, and staminal hairs as rewards for pollinators. The presence and function of staminal hairs with tip cells inOsyris alba has been reported for the first time. Female flowers are rewardless, producing neither mature pollen, nectar nor staminal hairs, but possess three modified yellow indehiscent anthers containing no viable pollen which may provide a strong visual feeding stimulus for pollinators. It is suggested that pollinators are attracted by deceit to female flowers by mimicry of the males and the floral mimicry is, therefore, intraspecific and intersexual. The floral characteristics and flowering phenology of male and female plants are consistent with this kind of mimicry. The female flower possesses a tricarpellary ovary with three ovules of which only one develops. The single seed, containing a small embryo and a large, rich endosperm, is borne in a red fleshy bird-dispersed fruit. The reduction in seed number per flower to one highly nutrient-invested seed, together with a reduction of the multiflowered inflorescence to a solitary flower and the sequential production of ripe fruits over an extended fruiting season, suggest that the female function is markedly resource-limited. It is suggested that, although all the reproductive characteristics present inOsyris alba, as well as hemiparasitism, had probably evolved before the end of the tropical Tertiary, they are of adaptive advantage in the nutrient and water-limited environment of the Mediterranean maquis.     

The chironomid fauna of the Mediterranean region reviewed

From the Mediterranean countries, Italy, France (southern), Spain, Portugal, Morocco, Algeria, Tunisia, Lebanon, Syria, Turkey, Greece and Yugoslavia and according to published and as yet unpublished data, about 703 Chironomid species are known. 97 of the species are exclusive to the Mediterranean region. For three speciesCricotopus beckeri, Eukiefferiella bedmari andParatanytarsus mediterraneus a pointdistribution map is given.29 species listed with an Afrotropical distribution also reach into various parts of the Mediterranean area. As an example, a point-distribution map ofParatrichocladius micans is given. Seven species with a Panpalaeotropical distribution are known in the Mediterranean region. The great majority of the other 570 species (81%) most likely have a Palaearctic distribution. However, accurate distribution data of many species are as yet not available. This holds in particular for species with an assumed Southpalaearctic distribution. For chironomids of the Mediterranean fauna a differentiation into Circum- and West-Mediterranean subgroups is not yet possible. The Afrotropical species reach the Mediterranean region chiefly by the Nile valley. Nevertheless, some apparently relict Afrotropic species in the South of Morocco may suggest a West-African progression towards the Mediterranean. The Syrian-East African rift valley may also be considered as a migration path for West Palaearctic and especially Oriental chironomids into the Afrotropic region.     

Dynamics of cohorts of cladodes and related effects on reproduction in the shrub Retama sphaerocarpa in semi-arid south-eastern Spain

Changes in the size and age structure of the canopy of the leguminous shrub Retama sphaerocarpa in semi-arid south-eastern Spain were investigated by monitoring growth and survivorship of cladodes (photosynthetic stems) on marked shoots over a period of 26 months. Three basic morphological types of cladodes – long shoots, short shoots, and secondary short shoots – were distinguished.The canopy of the shrubs contained three annual cohorts of cladodes in spring and summer. The number and size of shoots produced each year was highly variable and was apparently related to the amount of rainfall during the preceding cool season. The spring cohort of 1994 produced only 37% of cladodes compared with 1993. Two cohorts of shoots were actually initiated in spring and late summer of each year, but the second cohort produced only 2–12% of the number of cladodes compared with the spring cohort. The proportions of the different cohorts in the canopy changed rapidly from April to August, but only slowly during the remainder of the year when only two annual cohorts remained after extensive litterfall in late summer. This late summer litterfall caused a substantial reduction in green canopy area (40–50%) which was achieved mainly be shedding of one year old cladodes. The life expectancy of cladodes decreased with increasing order of their morphological type from 850 ± 25 days in long shoots to 563 ± 4 days and 546 ± 9 days in short shoots and second order short shoots, respectively.Flowering and fruiting took place from May to July, almost exclusively on one year old cladodes, and coincided with the maximum development of the canopy. Flowering intensity was high in 1994, when individual shoots supported a mean number of approximately 150 flowers. Shoots produced an average of 12.6 ± 0.6 and 5.3 ± 1.0 fruits per shoot in 1993 and 1994, respectively. Most of the annual fruit crop (80–90%) was shed during litterfall in late summer. A proportion of 10–20% was retained in the canopy for up to 12 months, however, with some fruits persisting for more than 22 months.     

Chlorophyll fluorescence parameters of three Mediterranean shrubs in a summer-autumn period in central Portugal

The photosynthetic performance of Cistus crispus, Centaurea africana and Thymus villosus, three shrubs of the Mediterranean-type maquis vegetation of Central Portugal, were studied between July and December 2003 by means of in vivo chlorophyll a fluorescence measurements. In C. africana total leaf decay occurred between August and October, in T. villosus no clear pattern of variation of the basal fluorescence (F_o) was observed, and in C. crispus an increase of this parameter was observed in late autumn. In all species, the limitation to photosynthesis by photoinhibition and the contribution of non-reversible processes to total photoinhibition were more pronounced in the summer than in the autumn. However, a pronounced decrease of the effective quantum yield of photosystem 2 (Φ_PS2) was found in late autumn, probably due to a decrease of the carboxylation efficiency of the Calvin-Benson cycle, which was also supported by a parallel decrease of the photochemical quenching coefficient (qP).     

First record of Cephalopholis taeniops (Valenciennes) in the Mediterranean Sea

Two specimens of African hind Cephalopholis taeniops (Valenciennes, 1828) are recorded for the first time in the Mediterranean Sea, in the coastal area of Gulf of Syrte, Libya. This finding represents an additional case of a tropical species of fish of West African origin in the Mediterranean Sea.     

The interaction between Cistaceae and a highly specific seed-harvester ant in a Mediterranean scrubland

We studied the interaction between the ant Goniomma kugleri and Cistaceae in a Cistus ladanifer -dominated scrubland, in southwestern Spain. We monitored seed harvesting, and studied ant preferences among Cistaceae seeds and their capture efficiencies for preferred seeds. For the stand of C. ladanifer , we estimated seed losses due to the ants. Harvesting was restricted to two seasons: mid-autumn to late winter, and late spring. Ant diet relied on Cistaceae seeds: during autumn and winter 90% of seeds returned to nests were of C. ladanifer , and the remaining fraction also comprised Cistaceae seeds. At this time, the ants harvested seeds directly from the plants. In late spring, the ant diet consisted of Tuberaria guttata s.l. seeds. Goniomma kugleri selectively collected Cistaceae seeds. For preferred species, seed removal rates at the colony level and seed capture times invested by individual workers were correlated with seed size. Because of shorter capture time and higher success frequency, capture efficiency in terms of number of seeds captured per unit time was higher for small-seeded species. Although each ant colony collected large numbers (up to 10⁵) of C. ladanifer seeds over the autumn–winter season, the impact of ant removal on the annual seed output was moderate, at around 20%. It is likely that, in C. ladanifer , the staggered seed release period, and the pulsed exposure of seed clumps in capsules through progressive locule dehiscence, effectively minimise seed losses to the ants.     

Messinian vegetation maps of the Mediterranean region using models and interpolated pollen data

This study proposes to compare the outputs from the CARAIB vegetation model forced by results from the LMD General Circulation Model with interpolated pollen data (Kriging method) from the Mediterranean region during the Messinian. The vegetation maps that have been obtained represent distinct phases of the salinity crisis: before the crisis and during the marginal evaporitic phase (interpolated map), and during the complete desiccation phase (simulated map). However, they are comparable in terms of vegetation density and agree on a strong contrast between the Northern (forest vegetation) and Southern (open vegetation) Mediterranean regions. Main differences concern the type of forests in the northern Mediterranean region, which are explained by discrepancies between precipitation amount predicted by the model and that calculated by a transfer function using pollen records. The interpolation method has been successfully tested in France using interpolated current pollen records by comparison with the present-day potential vegetation map. The resulting Messinian map is useful to validate or improve model simulation which does not take into account the depth of the Mediterranean Basin when it dried up. The Southern Mediterranean landscapes were open, with a steppe-like vegetation to the West and a savannah-like vegetation to the East. Forests prevailed to the North, organized in a mosaic system mainly controlled by relief. Such a contrast provides some explanation of the large number of deep fluvial canyons cut on the Northern margin at opposed to the South during the Mediterranean desiccation.     

Biennial variation in production of new shoots in groves of the giant bamboo Phyllostachys pubescens in Sichuan,China

The phenological pattern of fifteen Mediterranean phanaerophytes has been studied in several sites per species, by visiting the populations on a monthly basis over a one year period. Studied phenophases were dolichoblast vegetative growth (DVG), flower bud formation (FBF), flowering (F), fruit setting (FS), seed dispersal (SD), and leaf shedding of dolichoblasts (LSD). Considering the whole set of species, DVG, FBF and F took place mainly in spring, FS in summer, SD in autumn and LSD in summer and in autumn. Interspecific comparisons showed a wide variety of phenological patterns, which have been sorted according to the 'phenophase sequence index' (PSI). This index quantified the degree of superposition between DVG, FBF and F, and it constituted the basis for a functional classification of phenological patterns. Two groups were established. The 'type I' group was characterised by the concentration of phenophases in a short time in spring, while the 'type II' by the protraction and sequential arrangement of phenophases. Type I species performed most of their functions during a resource surplus period, but they have to face an intraplant competition between vegetative and reproductive demands. Type II species avoided intraplant competition but had to develop part of DVG, FBF and F during sub-optimal periods. It is hypothesised that type I species possess deeper roots, rely on predictable water sources and occupy mature stages of succession. Type II species, on the contrary, are expected to depend on more unpredictable water sources, to possess shallower root systems and to colonise earlier stages of succession. Intraspecific variability of phenology was found to be low among populations of the same species. Bud structure, which is a phylogenetic trait, may exert important constraints on plant phenology.Nomenclature: Flora Iberica – Castroviejo et al. 1986–1997, Flora Europaea – Tutin et al. 1964–1980.     

Comparison of ecosystems in the Mediterranean Basin and Western Australia

A comparison between fire-prone ecosystems in the Mediterranean basin and Western Australia shows convergent adaptations in structure, life forms and flora evolution. Both areas have in common summer drought and winter rainfall. Reproductive biology is mainly correlated with fire ecology; the different length of human impact and history seem to be responsible for floristic divergency in both areas. The ecological significance of pollination by insects, birds and mammals and problems of the seed banks are discussed.