The Benefits of Nest Relocation Extend Far Beyond Recruitment: A Rejoinder to Mrosovsky

Individual sea turtle nests have an extremely low probability of producting adult turtles; thus the practice of moving nests away from the ocean (where they will not be inundated by seawater) is a questionable conservation strategy. Recently in Environmental Management, Mrosovosky used the repeatability of nesting female turtles to place their eggs in certain locations to infer that some females may consistently nest in areas which will be flooded, lowering the chance that any eggs will hatch. This information was used to hypothesize that saving “doomed” sea turtle nests may then alter the genetic composition of the population, ultimately resulting in turtles that nest in poor habitats. Here I question Mrosovosky’s argument by focusing on several weaknesses inherent in the original article, namely that at present there is no evidence to suggest that nest-site selection is a heritable trait with an underlying genetic basis.     

Optimal timing of comb construction by honeybee (Apis mellifera) colonies: a dynamic programming model and experimental tests

Honeybee colonies, like organisms, should exhibit optimal design in their temporal pattern of resource allocation to somatic structures. A vital colony structure is the comb which stores honey for overwinter survival. However, the timing of comb construction poses a dilemma to a colony attempting to maximize its honey reserves. On the one hand, plenty of empty comb is needed for efficient exploitation of temporally unpredictable flower blooms. On the other hand, because comb is made from energetically expensive wax, its construction too early or in excessive amounts will reduce the amount of honey available for winter thermoregulation and brood-rearing. A dynamic optimization model concludes that colonies should add new comb only when they have filled their old comb with food and brood above a threshold level. The threshold increases with time until, at the end of the season, building is never an optimal behavior. The temporal pattern of construction predicted by the model – pulses of building coincident with periods of nectar intake and comb fullness – matches that seen in an actual colony observed over the course of an entire foraging season. When nectar sources are rich but temporally clumped, the model also predicts that bees should be sensitive to nectar intake, employing much higher thresholds on days when nectar is not available than on days when it is. Even under poorer and more dispersed nectar regimes, little fitness cost is paid by colonies replacing the optimal strategy with a simpler rule of thumb calling for new construction only when two conditions are met: (1) a fullness threshold has been exceeded, and (2) nectar is currently being collected. Experiments demonstrate that colonies do in fact use such a rule of thumb to control the onset of construction. However, once they have begun building, the bees continue as long as nectar collection persists, regardless of changes in comb fullness. Thus the onset and duration of comb-building bouts appear to be under partially independent control. Received: 30 October 1998 / Received in revised form: 14 December 1998 / Accepted: 16 January 1999     

A nesting association between semi-colonial Bullock's orioles and yellow-billed magpies: evidence for the predator protection hypothesis

Mixed-species nesting associations have been reported for many birds. However, few studies have shown that one species specifically chooses to nest close to another in order to obtain a direct benefit and only two studies have managed to adequately test the predator protection hypothesis for such associations. Here we demonstrate a nesting association between Bullock's orioles (Icterus galbula bullockii) and yellow-billed magpies (Pica nuttalli). The evidence indicates that this is an active association in which, given a choice of suitable habitat areas in which to nest, orioles choose those areas that contain magpie nests. Oriole nests associated with magpie nests have a significantly reduced predation rate compared to those without associated magpie nests. This suggests that orioles prefer to nest near to magpies and that this preference has evolved due to the protection provided by neighbouring magpies. The nesting association results in the clumping of oriole nests around magpie nests, and therefore provides a possible explanation for the semi-colonial nature of Bullock's orioles. Received: 23 November 1998 / Received in revised form: 25 May 1999 / Accepted: 30 May 1999     

Modelling cyanobacteria in shallow coastal seas

There is an increasing need to describe cyanobacteria bloom dynamics using ecosystem models. We consider two fundamentally different ways how cyanobacteria are currently implemented: a simple approach without explicit consideration of the life cycle which assumes that cyanobacteria grow due to nitrogen fixation alone and an advanced approach that computes the succession of four different stages of the cyanobacteria life cycle based on internal quotas of energy and nitrogen. To qualitatively and quantitatively intercompare these different approaches and with observations, we use the Baltic Sea ecosystem model ERGOM coupled to the one-dimensional water column model GOTM. Four experiments are carried out: three, using the simple approach with either (a) a prescribed constant minimum production, (b) no minimum value or (c) a prescribed constant minimum concentration, and one with (d) the full predictive life cycle. The model data of 35 years (1970-2005) are analyzed for the timing of the bloom, the interannual variability, the annual mean nitrogen fixation rates and the effect of cyanobacteria on eukaryotic phytoplankton. The results show significant differences. In the climatological seasonal mean, only the advanced approach which resolves the life cycle produces a realistic bloom onset and duration. The interannual variability of blooms is unrealistically small in the experiments with a prescribed minimum value. Annual mean nitrogen fixation rates diverge by up to 30% between the four model solutions. Finally, the representation of the cyanobacteria also influences the seasonal cycle of eukaryotic phytoplankton, i.e., flagellates. This study demonstrates that the way how cyanobacteria are implemented in coupled biological-physical models strongly determines the fluxes into the system and between the individual compartments.     

Efficiency and regulation of recruitment during colony emigration by the ant Temnothorax curvispinosus

Recruitment helps insect societies by bringing individuals to places where work needs to be done, but it also imposes energetic and opportunity costs. The net effect depends both on recruitment efficiency and on the ease with which insects can find work sites on their own. This study examined both of these factors for colony emigration by the ant Temnothorax curvispinosus. Emigrations were organized by a corps of active ants who transported the rest of the colony. These active ants either found new sites independently or followed tandem runs led by successful scouts. Although most tandem runs broke apart before reaching their target, even lost followers found the new site faster than did unguided searchers. When the new site was near the old nest, tandem runs were rare and summoned only a small proportion of the transporter corps. When the new site was instead distant and inconspicuous, tandem runs were common and brought roughly one third of the transporters. This pattern likely results from the quorum rule used by individual scouts to decide when to switch from tandem runs to transports. By monitoring how many nestmates have already found the nest, the ants ensure that the costs of recruitment are born only when necessary.     

Cost-effective nutrient reductions to coupled heterogeneous marine water basins: An application to the Baltic Sea

In this paper, the role of nutrient transports between marine basins is investigated for cost-effective solutions to predetermined marine basin targets. The interdependent advective nutrient transports as well as retentions among the seven major marine basins of the Baltic Sea are described by input-output analysis. This is in contrast to prior economic studies of transboundary water pollution that include only direct transport between the basins. The analytical results show that the difference in impacts between transport specifications depends mainly on the openness of the basins, that is, their transports with other basins. The application on Baltic Sea shows significant differences in costs and policy design between the nutrient transport specifications. The reason is that the Sea is characterized by long water and nutrient residence times, so relatively large part of nutrients are transported among basins.     

Estimates of (239+240)Pu inventories in Gdańsk Bay and Gdańsk basin

This paper presents and discusses the results of (239+240)Pu determinations in different components of Gdańsk bay and Gdańsk basin ecosystem, as well as estimated sources and inventories of plutonium in these basins. The total plutonium (239+240)Pu activities deposited in Gdańsk bay and Gdańsk basin sediments are 1.18 TBq and 3.77 TBq, respectively. Two rivers, the Vistula and Neman rivers, and atmospheric fallout were distinguished as the main sources of plutonium in these basins. In seawater (with suspended matter included) there is about 2.33 GBq (239+240)Pu (0.2% of total activity) in Gdańsk bay and 9.92 GBq (239+240)Pu (0.3% of total activity) in Gdańsk basin. In both cases, 56% of (239+240)Pu is associated with suspended matter. Organisms contain 3.81 MBq in Gdańsk bay and 7.45 MBq (239+240)Pu in Gdańsk basin. From this value in Gdańsk bay 82.1% of plutonium is associated with zoobenthos, 13.6% with phytobenthos, 1.6% with phytoplankton, 1.5% with zooplankton and 1.2% with fish. In Gdańsk basin, 83.2% is associated with zoobenthos, 7.5% with phytobenthos, 3.6% with phytoplankton, 3.2% with zooplankton and 2.5% with fish.     

A multi media load model for the Baltic Sea

The background of this work is the international decision process with regard to the selection of chemicals to be assessed with priority. In order to stress the precautionary principle, mass flows were analysed rather than concentrations, threshold values, etc., as preferred by the chemical legislation (which still excludes the marine area). Lindane, hexachlorobenzene (HCB), trichloroacetic acid and its sodium salt, medium-chained chlorinated paraffins and tributyltin (TBT) were selected due to their great relevance for the marine area. Trichloroacetic acid is an interesting model compound on account of its accidental formation by degradation of volatile chlorinated hydrocarbons and during chlorination processes. In addition, a hypothetical compound was modelled, representing a highly water-soluble substance with low vapour pressure. The balancing area is the Baltic Sea and its catchment area. In order to model the substance flows, the 'Input/Output-load model' has been developed. The model quantifies the shift and the distribution of a yearly load of the substance investigated from the terrestrial-limnic into the marine compartment (Baltic Sea). Water-soluble substances, which are usually considered to be of no concern, may enter the sea in great amounts and, if not degradable, remain there. It turned out to be necessary to take into account remobilisation, unintended formation and point as well as line-sources.