Geographical gradients in seed mass in relation to climate

Aim To determine whether latitudinal and longitudinal gradients in seed mass are related to variation in climatic features including temperature, solar radiation and rainfall. Location Australia. Methods Seed mass was estimated from over 1600 provenances covering the latitudinal and longitudinal extents of 34 perennial Glycine taxa in Australia. Climatic data were obtained from ANUCLIM 5.1 for collection locations based on long‐term meteorological records across Australia. These climatic data were subject to principal components analysis to extract three components as climatic indices. Generalized linear models were used in three separate sets of analyses to evaluate whether seed mass–latitude and seed mass–longitude relationships persisted after taking climatic variation into account. First, relationships were examined across species in analyses that did not explicitly consider phylogenetic relationships. Secondly, phylogenetic regressions were performed to examine patterns of correlated evolutionary change throughout the Glycine phylogeny. Within‐species analysis was also performed to examine consistency across different taxonomic levels. Results Geographical variation in seed mass among species was related primarily to temperature and solar radiation, while rainfall was much less influential upon seed mass. Partialing out the influence of temperature and solar radiation in models resulted in the disappearance of significant seed mass–latitude and seed mass–longitude relationships. Patterns within species were generally consistent with patterns among species. However, in several species, factors additional to these climatic variables may contribute to the origin and maintenance of geographical gradients in seed mass, as significant seed mass–latitude and seed mass–longitude relationships remained after controlling for the influence of climatic variables. Main conclusions Our empirical results support the hypotheses that (1) seed mass is larger at low latitudes and in the interior of the Australian continent due to increased metabolic costs at high temperatures, and that (2) higher levels of solar radiation result in an increase in the availability of photosynthate, which in turn leads to an increase in biomass for the production of large seeds. In effect, our findings show that greater energy is available precisely where needed, that is, where high temperatures require large seed mass on the basis of metabolic requirements.     

Patterns in species richness and distribution of vascular epiphytes in Chiapas, Mexico

Aim We aim to assess regional patterns in the distribution and species richness of vascular epiphytes with an emphasis on forests that differ in altitude and the amount of rainfall. Location Tropical America, in particularly the 75,000 km² large state of Chiapas in southern Mexico at 14.5–18.0°N. Chiapas is diverse in habitats with forests from sea‐level to the tree‐line at c. 3800 m altitude and with annual amounts of rainfall ranging from 800 to over 5000 mm. It is also one of the botanical best‐explored regions in the tropics. Methods First we give an overview of epiphyte inventories to date. Such epiphyte surveys were mostly carried out on the basis of surface area or individual trees and we discuss their problematic comparison. Applying a different methodological approach, we then used 12,276 unique vascular epiphyte plant collections from Chiapas that are deposited in various botanical collections. The locality data were georeferenced and compiled in a relational data base that was analysed using a geographical information system. To compare the number of species between inventories that differed in the numbers of records, we estimated the total richness, S_Chao, at each. Results We recorded 1173 vascular epiphyte species in thirty‐nine families (twenty‐three angiosperms), comprising c. 14% of all confirmed plant species in the state. About half of all species were orchids (568). Ferns and bromeliads were the next species‐rich groups with 244 and 101 species, respectively. Most species were found in the Montane Rain Forest and in the Central Plateau. Trees of different forest formations, rainfall regimes, altitudes and physiographical regions supported a characteristic epiphyte flora. Main conclusions We were able to confirm the presumed presence of a belt of high diversity at mid‐elevations (500–2000 m) in neotropical mountains. In contrast to predictions, however, we observed a decrease in diversity when the annual amount of rainfall exceeded 2500 mm. The decrease is attributed to wind‐dispersed orchids, bromeliads and Pteridophyta that may find establishment problematical under frequent downpours. In the wet but seasonal forests in Chiapas, this decrease is not compensated by plants in the animal‐dispersed Araceae that are abundant elsewhere. We presume that in addition to the annual amount of rainfall, its distribution in time determines the composition of the epiphyte community.     

Distribution and ecology of Demospongiae from the circalittoral of the islands of the Aegean Sea (Eastern Mediterranean)

Size-selective predation by fish is often considered to be a primary driver of seasonal declines in large-bodied Daphnia populations. However, large Daphnia commonly exhibit midsummer extinctions in ponds lacking planktivorous fish. A number of empirical and theoretical studies suggest that resource competition and its interaction with nutrient enrichment may determine variable dominance by large Daphnia. Low resource levels may favor competitive dominance by small-bodied taxa while large Daphnia may be favored under high resource conditions or following a nutrient/productivity pulse. Nutrient enrichment may also influence the strength of invertebrate predation on Daphnia by affecting how long vulnerable juveniles are exposed to predation. We investigated these hypotheses using an in situ mesocosm experiment in a permanent fishless pond that exhibited seasonal losses of Daphnia pulex. To explore the effects of nutrient enrichment, Daphnia plus a diverse assemblage of small-bodied zooplankton were exposed to three levels of enrichment (low, medium, and high). To explore the interaction between nutrient enrichment and invertebrate predation, we crossed the presence/absence of Notonecta undulata with low and high nutrient manipulations. We found no evidence of competitive reversals or shifts in dominance among nutrient levels, Daphnia performed poorly regardless of enrichment. This may have been due to shifts in algal composition to dominance by large filamentous green algae. Notonecta had significant negative effects on Daphnia alone, but no interaction with nutrient enrichment was detected. These results suggest that Daphnia are not invariably superior resource competitors compared to small taxa. Though predators can have negative effects, their presence is not necessary to explain poor Daphnia performance. Rather, abiotic conditions and/or resource-based effects are probably of greater importance.     

Nest Building in Captive Gorilla gorilla gorilla

Although various aspects of gorilla nest building have been described in wild populations, nest-building behavior of captive gorillas has not been subject to much scientific review. We observed nest building in 17 gorillas during three periods: summer baseline, winter baseline, and winter treatment, in which the amount of available nesting material was doubled. We conducted observations exclusively in the indoor holding area in the hour following evening departure of animal care staff. During baseline, gorillas engaged in nest-building on 3.1% of scans and were on a constructed nest on 27.9% of scans. Overall, gorillas spent significantly more time on elevated nests than on floor nests. There were no statistically significant sex, age class, or rearing history differences in nest building, time spent on a nest, or nest location preference. Nest building consisted of both gathering and manipulating materials. The gorillas spent significantly more time building nests in winter than in summer. Additionally, they were more often on elevated nests during winter than summer. Doubling the amount of nesting material did not increase nest building, but it increased the number of floor nests. Our results suggest that providing adequate materials to captive gorillas for nest building may facilitate performance of species-typical nest-building, minimize competition among individuals for nesting sites and materials, and permit individual thermoregulation.     

气象因子与地表植被生长相关性分析

降水和气温是影响地表植被覆盖状况的两个重要的气象要素,地表植被的生长对它们的响应又存在一定的滞后效应。利用我国334个气象台站和1982-1994年NOAA-AVHRR卫星数据,通过相关分析研究了我国4-7月份气候区域降水和活动积温对地表植被的影响。结果显示,不同的气候区域和月份,降水和积温对地表植被的作用程度明显不同;前期降水和活动积温对植被作用的有效时间尺度也分布不均,并与土壤质地类型分布有关,因此,通过某一固定时间尺度的降水或活动积温不能准确的预测大区域地表植被的生长状况。     

Virioplankton and microbial communities in aquatic systems: a seasonal study in two lakes of differing trophy

1. The seasonal and vertical distribution of the abundance of virus‐like particles (VLPs), together with the abundances of other microbial organisms (bacteria, unpigmented and pigmented nanoflagellates and ciliates), were determined in an oligomesotrophic lake (Pavin, France) and in a eutrophic lake (Aydat, France) between March and December 2000. 2. The abundance of the viral plankton and those of other microbial taxa were significantly higher in the more productive system. The same was for the virus‐to‐bacteria quotient (VBQ), which averaged seven in Lake Pavin and nine in Lake Aydat. 3. The abundance of viruses increased during the period of thermal stratification in both lakes, with the highest values being recorded at the end of summer/early autumn in the epi‐ and the metalimnion. The seasonal pattern of abundance of viruses in both lakes in the surface layer was similar, indicating that the dynamics of viruses may be controlled by environmental factors such as light conditions. 4. There was no correlation between the abundance of viruses and protists. We found correlations between viruses and heterotrophic bacteria in the whole water column in Lake Pavin, but only in the dark bottom waters in Lake Aydat. 5. Overall, the empirical findings in this study lead us to speculate that the weaker correlation between bacteria and viruses in Lake Aydat than in Lake Pavin, as well as the higher VBQ in the former, is a consequence of the increasing relative abundance of non‐bacteriophage VLPs along the trophic gradient of aquatic systems.     

Ciliate populations in temporary freshwater ponds: seasonal dynamics and influential factors

SUMMARY 1. The ciliate populations of two temporary ponds in southern Ontario were studied throughout their aquatic phases in 2001. Pond I (～1 ha) held water for 98 days, whereas Pond II (～0.25 ha) held water for 34 days. Populations were assessed both within the ponds themselves and within a series of enclosures in which invertebrate predator pressure was manipulated. 2. In the natural pond water, total ciliate abundance in Pond II rose rapidly from day 1 increasing two orders of magnitude by day 7. In contrast, total abundance in Pond I began at the same level as in Pond II but increased much more slowly, reached a plateau of around 500 individuals L^?1, and increased again late in the hydroperiod. 3. Despite being only 500 m apart, the two ponds were fairly dissimilar in terms of their species richness and species composition. Pond I contained 50 species compared with 70 species for Pond II, with only 24 species shared. Additional species occurred within the enclosures raising the total species richness to 145 species; 88 from Pond I, 104 from Pond II, with 47 species (30%) in common. Pond II contained more mid‐sized ciliates (50–200 μm), whereas Pond I was dominated by smaller ciliates, especially in mid‐May and early June. In Pond I, cumulative species richness throughout the hydroperiod was highest in the predator addition enclosures (65 ± 4 species), followed by the partial‐predator exclusion enclosures (50 ± 4). Lowest species richness was found in the control enclosures (39 ± 2) and in the pondwater controls (39 ± 0). Differences between the ciliates in the natural pond water and the enclosures appeared to be related to a greater concentration of phytoplankton within the enclosures (perhaps resulting from extensive growth of duckweed, Lemna, outside), and higher densities of zooplankters in the pond. 4. The physicochemical environment influenced species richness, total abundance and the number of rare species (27 in Pond II versus 13 in Pond I). Variation in ciliate abundance in Pond I could be explained by the number of days after filling (39%) and enclosure treatment (23%). These two parameters also explained 72% of the variation in species richness in Pond I (46 and 26%, respectively). Sixty‐five per cent of the variation in abundance in Pond II could be explained by the measured parameters: number of days after filling 27%, pH 19%, and nitrate levels 12%. Fifty‐two per cent of the variation in species richness was explained by the environmental parameters, of which pH was the most influential. Species succession was a strong feature of both ponds and its relationship to environmental variables and the presence of other organisms is discussed. 5. Addition of invertebrate predators resulted in higher abundance and higher species richness for a limited time period in one of the ponds – suggesting that differences in foodweb dynamics may influence ciliate community composition.     

Food Intake and Dietary Overlap in Native Lemur catta and Propithecus verreauxi and Introduced Eulemur fulvus at Berenty,Southern Madagascar

The introduction of Eulemur fulvus in 1975 into the Berenty Reserve and their recent attainment of population densities comparable to those of Lemur catta led us to analyze food partitioning among the 3 large prosimian species in the gallery forest. We assessed the diets of ring-tailed lemurs (Lemur catta), brown lemurs (Eulemur fulvus) and sifakas (Propithecus verreauxi) from food intake measurements during 3 successive short-term studies. All species exhibited marked seasonal changes in their major food categories. Dietary overlap was very high between ring-tailed lemurs and brown lemurs during 2 of 3 seasons, including the middle of the dry season. During the latter period, Eulemur appeared to compensate for a low quality diet by increasing the amount of food eaten. In contrast, Lemur fed on lower amounts of food and seemed more efficient at coping with fibrous plant materials. There is low dietary overlap of Lemur catta and Eulemur fulvus versus Propithecus, which exhibit by far the highest dietary diversity of the 3 species. We discuss sustainable coexistence among them, based on respective dietary adaptations and potential for dietary flexibility.