Plant–flower Visitor Networks In A Serpentine Metacommunity: Assessing Traits Associated With Keystone Plant Species

Consistent topology of plant–pollinator networks across space may be due to substitutability of the plant species most important for community function (keystone species). It is unclear, however, whether keystone species identity varies within a community type and what traits underlie this variation. Using a network biology approach, we assess whether keystone plant species vary across a metacommunity of five serpentine seeps in California and determine the features that predict their identity. We define keystone species as those with high strength, low node specialization index (NSI), and/or low d′ and determine whether these parameters are predicted by floral traits (flower biomass, number of open flowers per plant, symmetry, or stamen number) and/or ecological features (variation in local floral abundance, endemism) within seeps and across the metacommunity. Keystone species identity varied among seeps and was associated with local flower abundance: mean floral abundance correlated positively with strength but negatively with NSI within most seeps as well as across the metacommunity. For the metacommunity, flower biomass correlated negatively with NSI while variation in flower abundance correlated negatively with strength. Across the metacommunity, the d′ metric was associated with flower biomass, whereby plants with smaller flowers interacted with the most abundant pollinators across the metacommunity. Results suggest that connectance and interaction evenness may not be greatly influenced by community composition turnover due to substitution of keystone plant species across space. Keystone species can be predicted by functional traits but which trait (flower abundance or size) depended on the metric used and the level observed

Towards an adaptive model for simulating growth of marine mesozooplankton: A macromolecular perspective

Ultimately, the structure and functioning of marine ecosystems is defined by the transfer of autotrophic production to higher trophic levels and selective consumption of these autotrophs by predators. Hence, feeding regulation via modification of grazing and food incorporation by predators is critical for understanding and predicting the dynamics of ecosystems. In marine ecosystem and biogeochemical models, feeding regulation by consumers is assumed to be mainly dictated by food quality (Q), which is determined using food quality modules (FQMs) that mimic a consumers’ ability to anticipate fitness consequences for feeding on specific prey items. Current FQMs are based on frameworks that a priori identify specific food components, usually nitrogen (N), and/or phosphorus, as limiting. This negates the importance of consumer physiology, and ignores biochemical constrains on the limiting role of chemical elements in animal production. To help address these problems, we propose a new adaptive approach that bases Q on consumers’ capacity for food uptake and metabolic physiology. Uniquely, it (i) has separate pathways for the utilisation of carbon (C) associated with proteins, lipids and carbohydrates, (ii) considers stage-specific structural biochemical requirement of animals, and (iii) does not treat consumers’ structural demand for carbon as a “unitary requirement” but discriminates among the required biochemical forms of carbon. The approach is applicable to all heterotrophs. In the example given here the model has been configured to represent the calanoid copepod Acartia tonsa. Consistent with experimental observation, but unlike previous models, our model predicts the relationship between Q and food C:N to be unimodal with a maximum Q only at the threshold C:N for biomass production. Results suggest that prey C:N ratios may be irrelevant for food quality due to macromolecular biochemical constrains on the utilisation of chemical elements. This result emphasizes the importance of biochemical substances in animal nutrition and production as well as the necessity of developing food quality models able to adapt to the biochemical needs of the consumer

The ex-dividend day stock price anomaly: evidence from the Greek stock market

Ex-dividend day, Short-term trading hypothesis, Athens Stock Exchange, Tax clienteles, G12, G3,