Oecologia最新文献

Local soil temperature has the potential to affect plant phenology, which is a key indicator of the biological effects of climate change. Many existing analyses, however, ignore local temperatures and focus only on temperature at larger scales measured by weather stations. Ignoring local temperature adds noise to analyses, creating the need for longer time series, and may also bias results. Over four years, we investigated the effects of local soil temperature, sun exposure, and soil depth on flowering phenology for 35 populations of Canada mayflower (Maianthemum canadense) in an 82-hectare mixed deciduous forest in Newton, Massachusetts (USA). Flowering dates varied by 5-7 days among sites. Soil temperatures varied by about 5 °C across sites before and during the flowering season. Among the populations, plants flowered earliest at sites with the warmest local climates-around one day earlier for each 1 °C warmer temperature. Sun exposure and soil depth did not affect flowering times. Differences in temperature and flowering times among sites were consistent over the four years of the study. In most other published phenology studies, spring wildflowers flower 2-5 days earlier for each 1 °C of warming of air temperatures. This study demonstrates that the effects of local temperature on phenology can be investigated over relatively short periods of time and that these effects may bias estimates of phenological responses to temperature that rely solely on temperature data from weather stations.

The palm Lodoicea maldivica is marcescent, with dead leaves remaining attached to the trunk for an extended period. To investigate how this trait affects the distribution and turnover of dead leaf material in Lodoicea forest, we measured dead leaf production and standing crops of dead leaves attached to palms (D_M) and in the litter layer (D_L); for comparison, we measured D_L in stands of the non-marcescent species Martellidendron hornei and Deckenia nobilis. In a litterbag experiment, we investigated the decomposition of four types of leaf material: newly dead marcescent Lodoicea, old marcescent Lodoicea, and newly dead Deckenia and Martellidendron. Rates of decomposition were very slow and varied significantly amongst types (P < 0.001), with mean annual decomposition constants (k values) of 0.41, 0.37, 0.25 and 0.47 y^-1 for new and old Lodoicea, Deckenia and Martellidendron, respectively. Decomposition rates also varied significantly with location in the forest (P < 0.001), apparently due to variable moisture conditions resulting from the funneling of water by Lodoicea leaves. Compared to other tropical forests, N and P concentrations in dead leaves of all species were very low, while total quantities of dead leaf material were extremely high (24.0, 22.3 and 16.7 t dry weight ha^-1 for Lodoicea, Deckenia and Martellidendron, respectively). In the Lodoicea plot, marcescent leaves accounted for 46% (11.2 t dry weight ha^-1) of all dead leaf material. We discuss the ecological significance of marcescence and its implications for management, especially in making Lodoicea forest vulnerable to fire.

Temperate plants show a rapid seasonal turnover in various leaf traits and defenses. Such trends in plant defenses can potentially drive seasonal shifts in the specialization of insect herbivores. We quantified how non-volatile leaf metabolites, inducible volatile organic compounds (VOCs), C:N ratio and leaf toughness changed between the early, middle, and late seasons in five Salicaceae species and one Salix hybrid. We also explored seasonal trends in overall trait variation among the studied plants. We tested whether seasonal changes in dietary specialization of leaf-chewing larvae and adult beetles related to changes in the studied host-plant traits. Trait turnover occurred mainly through changes in VOCs and seasonal increase in traits that directly lower herbivore feeding efficiency. The overall variation in leaf traits was highest in the early season, with seasonal intraspecific variation being 33% smaller than the variation among species sampled at one time point. Although less frequently than we expected, the two groups of insect herbivores showed seasonal changes in specialization. The significant trends in herbivore specialization included peaks in the middle season for larval specialization based on VOCs and host phylogenetic relatedness and for adult beetle specialization based on C:N ratio plus leaf toughness. The detected species-specific trends in host-plant traits, their intraspecific variability, and differential trends among insect herbivores highlight the importance of considering seasonal variation when predicting trends in plant-herbivore interactions.

The tropical bat Mops plicatus feeds primarily on planthoppers, a major pest for rice farmers in Southeast Asia. This bat may help limit the spread of planthoppers by feeding on wind-dispersed individuals at high altitudes, providing an important ecosystem service. However, its foraging behavior during peak planthopper activity remains poorly understood. Therefore, we examined the three-dimensional foraging behavior of M. plicatus using miniaturized Global Positioning System loggers during peak emergence of planthoppers. We predicted that bats would spend most foraging time at high altitudes (i.e., > 110 m above ground), and use relatively large foraging ranges. Furthermore, we predicted that low-altitude flights would occur in paddy fields and high-altitude flights above forested sites on mountain ridges. Six of the 11 tracked bats used large foraging areas, covering between 40 to 1,740 km² during a single night. The median distance bats traveled per foraging trip was 60 km (range 27-217 km), with a median maximum distance from the cave roost of 26 km (range 13-95 km). Bats flew at a median altitude of 146 m above ground, yet occasionally reached more than 1,600 m above ground. Our results confirmed that M. plicatus foraged primarily at high altitudes for about 57% of their time. They preferred paddy fields and forests while avoiding water bodies. With its high-altitude flights and preference for planthoppers as prey, M. plicatus could help limit the spread of a major rice pest in Southeast Asia. Protecting this bat species could help support rice harvests throughout the region.

Fine roots play a crucial role in many ecological and biogeochemical processes in temperate forests. Generally, fine root biomass is expected to increase during the growing season, when water and nutrient demands are high, but information on seasonal variability is still scarce. Here, seasonal differences in root length of European beech (Fagus sylvatica L.) were analysed at eight sites within its north-eastern distribution range. Fine roots of mature trees were monitored using minirhizotrons. Scans were taken for three different depths at the beginning of winter, the end of winter and over the summer for two consecutive years, and analysed automatically by an AI-algorithm (RootDetector). An additional experiment was carried out to show that the RootDetector was unaffected by changes in soil moisture. Root-length density was 40% higher at the beginning of winter and 51% higher at the end of winter than in summer. Our results indicate a net root loss during adverse conditions in early summer, but no trend towards deeper root growth over these drier periods. Interestingly, the root loss was compensated afterwards during more favourable conditions in autumn. We could show that fine root length in temperate forests is seasonally more variable and, so far, less predictable than previously assumed. A profound understanding of this seasonal variability is important for modelling terrestrial biogeochemical processes and global carbon fluxes.

Competition is one of the key drivers of cladoceran community dynamics. Competitive abilities can be measured as the Threshold Food Concentration (TFC), i.e., concentration of food at which population growth rate equals zero. Species with lower TFC should be superior competitors. However, population TFC can vary with environmental conditions. We hypothesized that algal phosphorus (P) content influences TFC and can alter the outcome of competition between large and small-bodied cladocerans. We conducted competition and life table experiments with single clones of large Daphnia magna and small Daphnia longispina to assess how algal P content affected their TFC and competitive interactions. We also conducted computer simulations to further explore competition between the small and large species. Our experiments showed that TFC varied with the algal P content. P limitation increased the TFC of both species, but this increase was more pronounced for the smaller D. longispina. For this reason, D. magna was a superior competitor at low P content, while D. longispina was superior at high P content. We also found that enhanced food abundance gave an additional advantage to the large-bodied D. magna due to higher reproduction potential at high food concentrations.

Though there is mounting evidence that climate warming is altering trophic interactions between organisms, its effects on non-trophic interactions remain relatively undocumented. In seagrass systems, the bioturbating activity of infauna influences annual seagrass patch development by influencing seed burial depth and germination success as well as sediment properties. If bioturbation is altered by warming, consequences on seagrass may result. Here, we assessed how heatwaves alter seagrass seed burial depth and germination rates when no bioturbators (control), single bioturbators and mixtures of bioturbators of contrasting feeding activities are present. The three bioturbators manipulated were surface (top 1-2 cm of sediment) biodiffusor, the brown shrimp (Crangon crangon), the shallow (top 3-8 cm) diffusor, the common cockle, (Cerastoderma edule) and the upward (5-15 cm) conveyor, the polychaete, Cappitellidae spp. We applied two temperature treatments: (1) a present-day scenario set at the average summer temperature of seagrass habitat (17ºC); and (2) a heatwave scenario modelled on the maximum recorded temperature (26.6ºC). Under present-day conditions, seed burial was greater in the presence of bioturbators than the control where no infauna was added (42-74% vs. 33 ± 7%, respectively). Cockles had the greatest impact on seed burial amongst all the bioturbators. Under the heatwave scenario, seed burial in the mixed bioturbator treatment increased to match that of the cockle treatment. Cockles and polychaetes elevated the germination rates of buried seeds under present-day temperature, but not under the heatwave scenario. Overall, these results indicate that heatwaves have the potential both to amplify and disrupt non-trophic interactions, with implications for seagrass seed germination.

Plant communities with higher species richness and phylogenetic diversity can increase the diversity of herbivores and their enemies through trophic interactions. However, whether these two features of plant communities have the same positive influence on other guilds through non-trophic mechanisms requires further exploration. Dung beetles represent an ideal system for testing such impacts, as they do not have a specialized trophic interaction with plants and are sensitive to changes in vegetation structure and the associated microclimate. We used a dataset of dung beetles collected from forest sites, restoration plots, and cattle pastures to (a) determine whether the richness and phylogenetic diversity of plants within restoration plots influence the total biomass and the taxonomic, functional, and phylogenetic diversity of dung beetles; and (b) determine if the establishment of restoration plots allows to recover the abundance and diversity of dung beetle communities, relative to what is found in livestock pastures. In the restoration plots, the abundance of Scarabaeinae beetles and the total biomass, functional originality, and phylogenetic diversity of dung beetles were positively related to the number of plant species, but only the abundance of Scarabaeinae and total biomass of all dung beetles were positively related to the plant phylogenetic diversity. Finally, the restoration plots allowed a threefold increase in the total biomass of dung beetles relative to the biomass found in pastures. We discuss how restoration plots with high plant species richness and phylogenetic diversity can favor the recovery of dung beetle communities by potentially creating more niche opportunities.

Alien species can influence populations of native species through individual-level effects such as predation, competition, and poisoning. For alien species that possess strong defensive chemicals, poisoning is one of the most powerful mechanisms of individual-level effects on native biota. Although toxic alien species could potentially negatively affect survival (lethal effects) or life history traits (sub-lethal effects) of native predators via poisoning, previous studies have mainly focused on acute lethal effects. Thus, delayed effects on predator life history traits have been largely overlooked. To fill this knowledge gap, we conducted laboratory and field experiments to investigate whether toxic alien prey (hatchlings and tadpoles of an invasive toad, Bufo formosus) affect the survival and/or growth and development of a native predatory salamander (larvae of Hynobius retardatus) on Hokkaido, Japan. The laboratory experiment revealed that consumption of a single toad hatchling exerted non-lethal effects on salamanders, but suppressed both salamander growth and development of an ecological phenotype (broad-gape) normally induced by environmental conditions. Furthermore, the field experiment in a natural pond showed that the presence of toad hatchlings and tadpoles resulted in reduced salamander growth (smaller body size) and lower survival of salamanders in the later larval period. The results of the laboratory and field experiments are complementary evidence of the life history impacts of the toxic alien toad on native salamanders. Thus, the poisoning effects of toxic alien species can affect the life history of native predators even if they do not exert acute lethality.

Trophic niche has fundamental ecological importance, but many studies consider few niche metrics and most neglect critical structuring processes. Multiple processes shape trophic niches, including inter and intra-specific competition, predation and resource diversity. These processes interact and effects vary with time and taxa. The White Sands dunefield provides an ecological gradient ideal for understanding variation in niches. We measured population niche width, trophic position and individual specialization in four lizard species across habitats over 2 years. The habitats include White Sands interior, the surrounding desert scrub, and their ecotone. We used arthropod, lizard and plant stable isotopes to quantify niches. We sampled lizard competitors, predators and prey as proxies for ecological processes. We found substantial variation in niches across populations but convergence between species. Individual specialization and population niche width were surprisingly decoupled. Specialization was highest in habitats with low species diversity (White Sands) and population niche width highest at intermediate diversity (ecotone). White Sands lizards may exhibit 'ultra partitioning'; high specialization alongside low individual niche widths. Population niche width is likely constrained within White Sands by low prey diversity. High ecotonal population niche widths may be due to fewer natural enemies than desert scrub but higher resource diversity than White Sands. Trophic position and specialization were positively correlated, suggesting stronger intraspecific competition at higher trophic levels. Prey diversity, inter and intra-specific competition, and predation all interacted to shape niches. Our results highlight the need for measuring multiple components of community structure and niches, as results are likely misleading in isolation.