bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distribution and abundance patterns of bird community and raptor populations in the Andaman archipelago
Authors: Thiollay Jean‐Marc 
Published: July 2006

A qualitative survey of the terrestrial bird community (sixty‐five species) and a quantitative analysis of the five‐diurnal raptor assemblage were earned out on 33 islands of the oceanic Andaman archipelago in the Bay of Bengal Among seven geographical parameters, island area was the main determinant of species richness for both the whole bird community and each category of species associated with four habitat types Species richness decreased most markedly with island size in the smallest islands and in open habitat species The rarest forest species were the most extinction prone with decreasing island size Specific habitat selection was the most prominent ecological correlate of inter island species distribution Observed species distribution patterns did not fit the random species placement or equprobable occurrence hypothesesRaptors were primarily forest species, two of them restricted to forest interior, two more tolerant of fragmentation and one naturally associated with mangroves Unexpectedly, the two rarest and most area sensitive raptors were the two smallest species with a strong active flight, whereas the most abundant and widespread species was the most forest interior and endemic taxon Both raptor species richness, species frequency of occurrence and abundance indices decreased with island area, which was consistently the most significant determinant of every species' occurrence and abundance There was a significant correlation between abundance or frequency of occurrence of every raptor species and the proportion of their preferred habitat type No relationship was found between habitat niche breadth or local abundance of any species and their distribution range among islands The hypothesis of random composition of species assemblages on islands was not supported because of species specific habitat selection Any evidence of interspecific competitive exclusion was limited to the striking habitat segregation of the two congeneric serpent eagles A metapopulation structure was suggested by small population distribution patterns, observed sea crossing and the circumstances of an apparent extinction
Secondary succession and summer herbivory in a subarctic grassland: community structure and diversity
Authors: Zobel Kristjan , Moora Mari , Brown Valerie K. , Niemela Pekka , Zobel Martin 
Published: July 2006

A field experiment was established in a subarctic grassland in the Finnish Lapland to study the role of summer herbivory in plant community succession Perennial vegetation and moss cover were removed in an area of 324 m2 The site was divided into four blocks, of which two were fenced to prevent herbivory by large mammals (reindeer, hare)Early successional changes in the vegetation were assessed Mean species richness per 3 × 3 m plot was consistently higher in the fenced area, indicating that herbivory can suppress small‐scale diversity Herbivory affected the height of several plant species However, there was no correlation between frequency and height of individual species There was a weak indication that taller species were more successful m early succession when grazed Light competition is apparently not a key process determining successional change Thus, in early stage of succession, summer herbivory has little effect on diversity by limiting light competition, and most species are equally successful in grazed and ungrazed plots There was some indirect evidence about competitive interactions in the developing community However, unlike temperate grasslands, large mammal herbivory and competition for light seem not to be important determinants of community change in this subarctic grassland (at least what concernes early successional stages) This may be explained by the harshness of local climate, and abundance of light due to the polar day
Evidence that humidity influences snake activity patterns: a field study of the Malayan pit viper Calloselasma rhodostoma
Authors: Daltry Jennifer C. , Ross Toby , Thorpe Roger S. , Wüster Wolfgang 
Published: July 2006

Multivariate statistical methods were used to elucidate which environmental factors influence the activity patterns of free‐living Malayan pit vipers, Calloselasma rhodostoma. Fourteen adult snakes were implanted with miniature radiotransmitters and located a total of 887 times in 5 months. The pit vipers usually remained coiled on the ground for several consecutive days before moving at night to a new site. Partial correlation tests revealed that the frequency and distance of movements to new sites by tagged snakes were highly positively correlated with ambient relative humidity, but not with rainfall, ambient temperature or the lunar cycle. This finding was corroborated by the frequency with which active non‐tagged C. rhodostoma were encountered at night, In each site, the proportion of the snakes’ bodies exposed to view was positively correlated with ambient humidity, and the snakes retreated to areas with deeper undergrowth when ambient humidity was low. Overt thermoregulatory behaviour was not observed, and implanted thermosensitive transmitters revealed that the snakes were passive thermoconformers.These findings seem lo contradict much of the current literature which shows temperature to be the dominant abiotic factor affecting reptilian activity, but most herpetologists have considered only temperate forms. Ambient temperature in our tropical study site was warm and relatively constant throughout the year (mean daily range = 24‐ 33°C), so the pit vipers could passively maintain body temperature within a fairly narrow range, with a daytime mean of 29.4°C. Ambient relative humidity, on the other hand, was very variable, and confining exposure and activity to periods of high ambient humidity may be necessary to avoid dehydration
Stability of pre‐ and post‐fire spatial structure of pine trees in Aleppo pine forest
Authors: Ne'eman Gidi , Izhaki Ido 
Published: July 2006

The study reported here describes for the first time the similarity between pre‐ and post‐fire spatial patterns of the trees in a Mediterranean pine forest demonstrating that the pre‐fire ancestor microsite is occupied also by the next generation. Although Aleppo pine Pinus halepensis Mill, is an obligatory post‐fire seeder, it is adapted to regenerate in its pre‐fire growing microsite. thus keeping suitable growing sites from generation to generation. We studied the effect of the dead burned adult pines on the density and size of their recruited saplings 2, 5, 11 and 20 yr after fire. A comparison of pine sapling density and size was made between the “near” zone (under the former effect of the burned canopy) and the‘far’zone (beyond the former effect of the burned canopy).In the site 2 yr after fire, seedling density was 56% higher in the “far” zone than in the‘near’zone, but seedling .size was similar. However in the site 20 yr after fire, densities were similar in both zones, but the size was bigger by 89% in the “near” zone. Thus, population recruitment after fire seems to peak near the burned pine trees rather than at u distance from them, in contrast to Janzen's original‘distance hypothesis’ model suggested for undisturbed rainforest. Mere we present a new hypothetical model for the spatial pattern of post‐fire regeneration of obligate seeder tree species forming open forests. It is proposed that in such trees the microsites which were kept by the burned adult trees, which are killed by the fire, are also the favorable regeneration microsite for the post‐fire generation.
Effects of wrack burial in salt‐stressed habitats: Batis maritima in a southwest Atlantic salt marsh
Authors: Pennings Steven C. , Richards Christina L. 
Published: July 2006

In coastal salt marshes, mats of wrack (dead plant stems) that are deposited on the marsh by high tides can kill underlying vegetation and initiate secondary succession. The importance of wrack disturbance in northwest Atlantic salt marshes has been a topic of recent debate. The importance of wrack disturbance in southwest Atlantic salt marshes, which experience a very different climate regime than do northern marshes, has rarely been examined. Working in a Georgia salt marsh, we documented a pattern of positive association between wrack and Batis maritima biomass, and conducted experiments that indicated that wrack was beneficial to Batis maritima. Sampling indicated that natural wrack deposition was correlated with areas of vigorous Batis growth and mild soil conditions. Natural wrack deposition occurred primarily at the highest elevations occupied by Batis maritima (the high Batis zone). Batis plants in the high zone were taller, with more and larger leaves, and contained several times the biomass/unit area than Batis plants at lower elevations. High zone soils had lower salinities, better percolation rates, and a lower organic content than did soils from lower elevations. Experimental manipulations demonstrated that deposition of wrack was partially responsible for these patterns. In each of two experiments, soil salinities were lower and plants taller and larger in the presence of wrack compared to in its absence. Although wrack lowered salinities and enhanced plant growth, the effects were not large enough to completely explain the differences between Batis zones. Instead, wrack probably reinforced pre‐existing gradients in flooding and salinity caused by differences in elevation and terrestrial runoff.Our results contrast with previous studies from northern marshes. Because of geographic differences in climate and plant phenology, northern marshes are more likely than southern marshes to receive patches of wrack thick enough to kill underlying vegetation. Plants covered by thin layers of wrack, as commonly occurs in southern marshes, may often grow through the wrack rather than suffer mortality. Also because of climatic differences, wrack is more likely to benefit plants by ameliorating salinity stress in southern marshes, where soil salinities are often hypersaline, than in northern marshes where soils are rarely hypersaline. Although ecological processes may differ between northern and southern salt marshes, these differences may be predictable based on an understanding of geographic variation in climate.
Individual variation and the effects of weather, age and flowering history on survival and flowering of the long‐lived perennial Gentiana pneumonanthe
Authors: Rose R. J. , Clarke R. T. , Chapman S. B. 
Published: July 2006

Gentiana pneumonanthe, the marsh gentian, is a declining species in both Britain and Europe as a result of loss of its heathland habitat or inappropriate management of that which remains. We analysed long‐term demographic data sets (1977‐1991) from four populations of the plant to test the hypotheses that an individual plant's survival and its chances of flowering in any year are related to its age and performance in previous years, taking into account the climatic conditions that existed in those years The results show that: 1)‘new’plants (2 yr old) had a higher mortality rate (mean = 20.8%) than‘young’(3 yr old) plants (mean = 5.0%), which in turn had a higher mortality than older, ‘mature’ (four or more year old) plants (mean = 3.8%): 2)‘new’ plants had a higher mortality rate after either a growing season with below average rainfall or an above average winter rainfall; 3) mortality of‘mature’plants was independent of age, indicating no evidence of senescence; 4)‘mature’plants had a higher mortality rate after above average rainfall during the previous winter; 5) plants that have flowered within the previous two years are most likely to flower in the current year indicating high individual variation in flowering performance‐ 6) more plants flower and flowering plants produced more flowers in the two years following a warmer than average growing season.The above factors are related to current site management and the implications are discussed. Suggestions are given for changes in management of the sites where this rare plant occurs.
Patterns of host use in solitary parasitoids (Hymenoptera, Ichneumonidae): field evidence from a homogeneous habitat
Authors: Teder Tiit , Tammaru Toomas , Pedmanson Rein 
Published: July 2006

Teder, T., Tammaru, T. and Pedmanson, R. 1999. Patterns of host use in solitary parasitoids (Hymenoptera, Ichneumonidae): field evidence from a homogeneous habitat. ‐ Ecography 22: 79‐86.We detected a significant inter‐ and intraspecific host preference on the level of individual host use in a system, in which three moth species (Lepidoptera: Noctuidae), feeding on a cattail Typha latifolia, are parasitized by three solitary parasitoid species (Hymenoptera: Ichneumonidae). The biology of the host species is similar but they exhibit remarkable inter‐ and intraspecific variance in body size. All the parasitoid species preferred the largest host species in this system whereas other host species were used only occasionally. We found that parasitoids which emerged from females of the preferred host species were larger than those which developed in males of the same species. Accordingly, two of the parasitoid species had a significant within‐host‐species preference: females of the largest moth species were used more often than males. No dependence of the preference pattern on host density was found. This pattern of host use is discussed in the light of the switching theory and the optimal host selection theory. Our results indicate that non‐random host use by parasitoids may have significant effects on host populations and communities, and forms a potential selective factor against large body size in herbivorous insects. Unlike the majority of ichneumonid wasps, these three parasitoid species have no remarkable female‐biased sexual size dimorphism, in accordance with the predictions of Charnov's sex allocation theory for this case, we did not observe any significant host quality dependent biases in sex allocation: there was no association between host sex and parasitoid sex, neither did parasitoid sex ratio differ between years with different host quality.
Dispersal of Spanish juniper Juniperus thurifera by birds and mammals in a fragmented landscape
Authors: Santos Tomás , Tellería José L. , Virgós Emilio 
Published: July 2006

Dispersal of Spanish juniper Juniperus thurifera was examined in a farming landscape of central Spain to study the effects of fragmentation on the dispersal effectiveness of the different dispersers. and the consequences for the plant. The study was conducted in two large forests (LF: 280 and 150 ha) representative of unfragmented conditions, and 18 small isolated fragments (0.1 ‐3 ha) which were classified in two groups: 1) F1, forest remnants with both high juniper cover and cone production (N = 5): and 2) F2, remnants in which fragmentation has caused a heavy reduction in junipers (N = 13). Cone production, disperser abundances and quantity of dispersal by birds (Turdus thrushes) and mammals (carnivores, rabbits and sheep) were estimated throughout two study years. Dispersal by thrushes was measured in three types of trees representing a decreasing attraction focus to birds: Spanish junipers with cones (SJI). Spanish junipers without cones (SJ2) and holm oaks (HO).Cone production greatly decreased from LF to F1 and F2 in both study years, affecting F2 dramatically. Thrush abundances were similar in LF and F1, but thrushes lacked or were very scarce in F2, Carnivores showed an even distribution throughout the whole area, but herbivores were relatively scarce in F2 fragments, especially rabbits, which were lacking in the fragments under 0.6 ha. Patterns of seed deposition around trees showed decreasing dispersal activity of thrushes from SJ1 (83.1% of the examined trees had seed‐packets thrush pellets) to SJ2 (53.6%) and HO (23.6%.). Both distribution patterns and density of pellets were roughly similar in LF and F1. but pellets were only recorded in one (SJ1) out of 159 trees examined in F2. supporting thrushes behaved as specialist feeders and thus avoided the patches devoid of juniper cones. Average densities of pellets in LF reached 397.6 pellets ha‐1, surpassing at least 30 times the quantitative effectiveness (seed‐packets ha‐1) of mammal dispersers. Juniper seeds were present but very scarce in the mammal faeces collected in both fragments F1 and F2. Overall, the quantitative effectiveness of carnivores was nearly 4 times lower in the fragments than in LF, and that of herbivores 11 times lower. This result is consistent with the lower availability of juniper cones in the fragments and. together the distribution of mammal abundances, fits the prediction that mammals (except rabbits) moved among landscape patches according to the total availability of food supplies.Overall, results showed that dispersal of Spanish juniper in fragments F2 is seriously impaired by the loss of their main dispersers (thrushes), and that recruitment became dependent upon mammal dispersers with a low quantitative effectiveness, namely carnivores and sheep.
Habitat fragmentation and large‐scale conservation: what do we know for sure?
Authors: Harrison Susan , Bruna Emilio 
Published: July 2006

We review the ecological effects of habitat fragmentation, comparing the theoretical approaches that have been taken to understanding it with the existing evidence from empirical studies. Theory has emphasized the spatial aspects of fragmentation and the role of dispersal among patches, and has generated interesting predictions such as a nonlinear relationship between the amount of remaining habitat and the probability of species persistence. However, while the few available large‐scale empirical studies of fragmentation all tend to show that it has major effects, these documented effects tend to be relatively simple ones such as the degradation of habitat quality within fragments. There is good reason to be cautious of any claim that corridors or the spatial configuration of remaining habitat can compensate for the overall loss of habitat.This is an invited Minireview on the occasion of the 50th anniversary of the Nordic Ecological Society Oikos.
The structure of a high latitude plant‐flower visitor system: the dominance of flies
Authors: Elberling Heidi , Olesen Jens M. 
Published: July 2006

The species richness of insect flower visitors to all angiosperms at a subarctic‐alpine site in northern Sweden was described and the plant‐flower visitor matrix was analysed and compared to other high latitude systems and with systems from lower latitudes. In the habitat, 23 plant species had a total of 242 interactions with 388 flower‐visiting insects, belonging to 118 taxa. Connectance of the plant‐flower visitor matrix was 8.9. Comparing our findings with other studies, we get that the proportion of dipteran species of the total pollinator fauna increases with latitude but that the proportions of species of Diptera, Hymenoptera and Lepidoptera do not vary significantly among high latitude systems. Muscidae and Empididae were more abundant and generalised than other dipteran families visiting flowers in the arctic, their proportions of the total Diptera fauna increase with latitude and they are the most widespread families of flower‐visiting insects in the arctic. Several Muscidae species are typical to alpine habitats in the arctic‐subarctic zone. These species have special pollen feeding behaviour and an elongated proboscis, which improves access to closed flowers.Compared to other published pollination system studies, the connectance of low latitude systems ranges between 3.4 and 28.1, whereas high latitude and high altitude systems vary between 8.6 and 19 (‐60).
Determinants of helminth aggregation in natural host populations: individual differences or spatial heterogeneity?
Authors: Haukisalmi Voitto , Henttonen Heikki 
Published: July 2006

We assessed the importance of spatial heterogeneity for the aggregation of helminth populations in the bank vole Clethrionomys glareolus (Arvicolinae) using a previously published method which allows to analyse parasite aggregation at two host population levels, i.e., within and between spatial samples of the host population.In the main empirical material from Finnish Lapland (Pallasjärvi), all five helminth species were significantly aggregated within study sites, but only three rare species showed significant aggregation among sites. In all helminth species, the total aggregation was primarily (79‐98%) determined by aggregation within sites, i.e., between host individuals. Despite the larger spatial scale and more heterogeneous landscape, the comparative material from South Finland (Luhanka) supported the generally high proportion of the total aggregation due to within‐site heterogeneity.Despite the clear interspecific differences in patchiness of helminth populations, the proportion of the total aggregation due to among‐site heterogeneity did not vary significantly among helminth species. The results indicate a link between aggregation at two population levels; species that showed strong within‐site aggregation were also characterised by pronounced spatial heterogeneity and significant among‐site aggregation.
Developmental strategies of Koenigia islandica, a high‐arctic annual plant
Authors: Heide Ola M. , Gauslaa Yngvar 
Published: July 2006

Seed germination, growth and flowering of the arctic‐alpine annual Koenigia islandica were studied in controlled environment. Intact (unabraded) seeds germinated poorely at temperatures up to 18°C, with an optimum at 24°C (89% in 10 d). Scarified seeds germinated rapidly, and reached 100% germination in 3 d at 21°C, but no >40% germination occurred at 9 and 12°C, The seeds had no light requirement for germination, nor did fluctuating temperatures improve germinationDry matter production was optimal at 12°C in both short day (SD) and long day (LD) conditions, but was markedly higher in LD than in SD at identical fluences at all temperatures except 21°C where the plants showed symptoms of severe heat stress. The temperature compensation point for net productivity was estimated to 24°C, and negative carbon balance at higher temperatures might be an important physiological mechanism limiting the distribution of K. islandica in Scandinavia.Flowering was extremely rapid and independent of daylength, even in a high‐arctic population from 79°N, In full summer daylight anthesis was reached 24 d after germination and seeds ripened after 36 d at 15°C, Days to anthesis varied little across the temperature range from 6 to 21°C, giving a linear decrease in the heat‐sum requirement for the attainment of flowering with decreasing temperature.It is concluded that conservative seed germination strategy, tininess and rapid development, low temperature optima for growth and reproduction, and daylength indifference of flowering are important adaptations for success of an annual plant in high‐arctic and high‐alpine environments, Daylength neutrality has facilitated the wide‐latitudinal distribution of K. islandica. including the penetration of the species to the southern hemisphere.