Epiphytic Ferns for Sale: Influence of Commercial Plant Collection on the Frequency of Platycerium stemaria (Polypodiaceae) in Coconut Plantations on the Southeastern Ivory Coast

Abstract: On the southeastern Ivory Coast, two coconut plantations were compared with regard to the frequency of the epiphytic fern Platycerium stemaria on coconut trees as influenced by plant collecting for commercial purposes. At each of the two sites, 250 coconut trees were investigated for the presence of P. stemaria and signs of collecting activity. General species richness of vascular epiphytes at the study sites was low, with only three other epiphytic ferns ( Asplenium sp., Microgramma owariensis, Phymatodes scolopendria ) being present. At study site no. 1, which was located directly behind several flower stalls offering P. stemaria for sale, the number of coconuts bearing living P. stemaria was significantly lower than at site no. 2 with no flower stalls in the immediate surroundings. At site no. 1, the frequency of P. stemaria was lowest in the neighbourhood of the flower stalls and increased with distance. Within a distance of less than 50 m from the flower stalls, ca. 70 % of the coconuts showed signs of P. stemaria collecting activity. Compared with site no. 1, the number of palm trees with living P. stemaria at site no. 2 was considerably higher ( ca. 20 %) and only three coconut trees showed signs of Platycerium collection. Over much of the Ivorian rain forest region where the forest has been cut or converted into agricultural land, plantation trees are important phorophytes (in particular cocoa trees). In many West African regions plantation trees form the last remaining sites for vascular epiphytes, which often occur with considerable abundance. In the Ivory Coast, the collecting of P. stemaria in coconut plantations causes locally a drastic decline in the population size. However, much more threatening to the long-term maintenance of epiphyte communities in plantations is their conversion into non-tree plantations (e.g., pineapples, bananas) or their replacement by urban structures and tourist facilities.     

Maintenance of zonation patterns in two species of flat periwinkle,Littorina obtusata and L. mariae

The zonation patterns of Littorina obtusata (L.) and Littorina mariae Sacchi et Rastelli were shown to be quite distinct on a sheltered rocky shore. L. obtusata was found at all the heights sampled; it reached peak numbers at mid shore on the alga Ascophyllum nodosum L. (Le Jol). There was no difference in the tidal height occupied by adults or juveniles; or in the mean size of L. obtusata along the vertical gradient of the shore. In contrast L. mariae occurred exclusively low on the shore, on Fucus serratus L. Translocation of the two species within their respective levels resulted in random movement after 4 days, although initial movements after 1 and 2 days were sometimes directional. Animals transplanted to the normal level of the other species showed directional movement towards their home zone; this was most pronounced after 4 days. There was no difference in the distance moved by the two species, although the distance moved did vary with tidal height, both species moving further at mid shore than low shore. Distances moved by littorinids at replicate areas in the low shore were similar but those at mid shore did vary. There was an interaction between the species and the different tidal heights which revealed that transplanted species moved further than translocated species at the same tidal level. However, this was only significant in the case of L. mariae. It is suggested that the close relationship between the winkles and their host algae may direct the homing behaviour of displaced individuals.     

Successional events following simazine application

Successional events of aquatic vegetation in a farm pond were studied, after application of simazine. After decay of the higher plants, phytoplankton did not dominate, instead herbicide-resistant seeds and subsurface structures of Potamogeton foliosus developed. Benthic algae covered and stabilized the bottom. Following stabilization, the water cleared and Chara vulgaris growth resumed wherever the substrate was firm.Suggestions are made as to how a pond can be managed to maintain the desired pioneer vegetation of Ch. vulgaris.     

Life history evolution and genome size in subtribe Oncidiinae (Orchidaceae)

• Background and Aims Within Oncidiinae, there are severalgroups of species that are effectively annuals, and we wishedto see if these species had smaller genome sizes than averagefor the subtribe. • Methods Fifty-four genome size estimates (50 of whichare new) for species in subtribe Oncidiinae (Orchidaceae) wereexamined for the first time in a phylogenetic context to evaluatehypotheses concerning genome sizes and life history traits. • Results and Conclusions Within the limits of still relativelysparse sampling, the species that are effectively annuals doappear to have smaller genome sizes than average. However, thegenome sizes of their immediate sister group are also small,indicating that changes in genome size preceded the change inlife history traits. Genome sizes and chromosome numbers alsodo not correlate; some slowly growing species have lower chromosomenumbers but large genomes and vice versa. Based on a surveyof the literature on orchids, it is also clear that epiphyticspecies have smaller genome sizes than do terrestrial species,which could be an effect of different water relations or thefact that most terrestrial orchids are geophytic or have distinctgrowth and dormancy phases.     

Species richness and abundance of epiphytic Araceae on adjacent floodplain and upland forest in Amazonian Ecuador

Terrestrial plant communities of adjacent upland and floodplain forest of the Amazonian lowland differ from each other in species richness and composition. Epiphytes are generally not considered as being affected by flooding, but we found considerable variation in the communities of epiphytic Araceae of flooded and unflooded forest. Contrary to findings from tree or ground herb communities, no depletion in overall species richness was observed among epiphytic aroids of the floodplains. Abundance and number of epiphytic aroid species per phorophyte were significantly higher than in upland forest, and the species composition varied conspicuously between the two forest types. We suggest that these differences are due to elevated humidity and better soil quality on the floodplains and reject the assumption that flooding has no effect on the epiphytic community.     

Niche assembly of epiphytic bryophyte communities in the Guianas: a regional approach

Aim Epiphytic bryophyte communities of tropical forests show a gradient in species composition from the base to the top of the host trees, indicating a strong role of niche assembly. This pattern, however, has never been tested at a regional scale. The aim of this study was to test whether niche assembly, rather than dispersal limitation, predominantly drives species composition of bryophyte communities across large spatial scales. Location Three lowland forests in the Guianas: one near Saul, French Guiana; and two near Mabura Hill, Guyana. Methods Communities of epiphytic bryophytes were sampled from six different height zones of several trees in three lowland forests. We analysed the composition of these communities using detrended correspondence analysis in order to find the best explanatory variable for the variation in community composition. A multi‐response permutation procedure was used to test the significance of grouping communities by height zone. We conducted an indicator species analysis to classify species as specialists or generalists and then tested, through weighted averaging, if specialists would indeed maintain their preferred height zone across the Guianas. Results Community composition was explained mainly by height zone. The similarity among communities inhabiting the same height zone of trees, across a distance of up to 640 km, was higher than the similarity among communities established along the vertical gradient of a single standing tree (30–50 m). More than half (57%) of the species had a preferred height zone, and the preference was consistent: species occupied roughly the same height zone on host trees in the different localities. The three local communities investigated were found to belong to the same regional species pool. Main conclusions Throughout the Guianas, epiphytic bryophyte communities are drawn from the same regional species pool, and their composition is shaped by micro‐environmental conditions. The predominance of niche assembly over dispersal assembly rules is consistently found at both local and regional scales.     

Phytoplankton and Epiphyte Development and Their Shading Effect on Submerged Macrophytes in Lakes of Different Nutrient Status

The annual mean light intensity at the depth limit of the Littorella vegetation was 24–33% of the subsurface light intensity, despite large variations in each attenuation component (lake water, phytoplankton, and epiphytes). In oligotrophic, silicate-poor lakes, the light attenuation above the submerged vegetation was dominated by the water itself, which accounted for 65–72% of the total attenuation. Phytoplankton and epiphytes were equal in importance to each other. In oligotrophic, silicate-rich lakes and lakes receiving a nitrogen supply above background level, the epiphytes were more abundant, accounting for about 50% of the light attenuation. In one lake with a high nutrient supply, the epiphytes were responsible for 86% of the light attenuation. A new method of measuring the effect of shading by the epiphytic community on submerged macrophytes is presented. The light attenuation caused by the phytoplankton and the epiphytes was investigated and related to the depth distribution of the submerged angiosperm, Littorella uniflora. It is shown that the biomass of the epiphytes increased more than the biomass of the phytoplankton in response to an external or internal nutrient loading. Shading by epiphytes is of decisive importance for the depth distribution of Littorella at increasing nutrient supply.     

Gracilaria conferta and its epiphytes: 3. Allelopathic inhibition of the red seaweed byUlva cf.lactuca

In a previous study (Svirski et al., 1993), it was found that growth inhibition ofGracilaria spp., when cultured in the presence ofUlva cf.lactuca, was not due to shading or nutrient depletion, but seemed to be caused by competition for inorganic carbon or some type of allelopathy. In the present study, we attempted to differentiate between these two possible influences by (1) growing the two algae in biculture under various conditions, but keeping inorganic carbon levels constant and measuring net photosynthesis, respiration and growth rates, and by (2) measuring growth rates ofGracilaria spp. in the presence of extracts derived from media previously used to growUlva cf.lactuca.Both net photosynthesis and growth rates ofGracilaria spp. in biculture were inhibited, despite CO₂ (and also HCO₃ ^–) levels being kept constantly high in the culture media. It is likely that these responses were due to markedly enhanced rates of dark respiration inGracilaria spp. when grown together withUlva cf.lactuca. Growth ofGracilaria spp. was also inhibited by extracts derived from seawater in whichUlva cf.lactuca had previously been grown. The strong inhibition by ethyl acetate and chloroform extracts indicate an allelopathic effect onGracilaria spp.