Simple Bioenergetic Model Research Articles

Modelling the impact of condition-dependent responses and lipid-store availability on the consequences of disturbance in a cetacean.

Lipid-store body condition is fundamental to how animals cope with environmental fluctuations, including anthropogenic change. As it provides an energetic buffer, body condition is expected to influence risk-taking strategies, with both positive and negative relationships between body condition and risk-taking posited in the literature. Individuals in good condition may take more risks due to state-dependent safety ('ability-based' explanation), or alternatively fewer risks due to asset protection and reduced need to undertake risky foraging ('needs-based' explanation). Such state-dependent responses could drive non-linear impacts of anthropogenic activities through feedback between body condition and behavioural disturbance. Here, we present a simple bioenergetic model that explicitly incorporates hypothetical body condition-dependent response strategies for a cetacean, the sperm whale. The model considered the consequences of state-dependent foraging cessation and availability of wax ester (WE) lipids for calf provisioning and female survival. We found strikingly different consequences of disturbance depending on strategy and WE availability scenarios. Compared with the null strategy, where responses to disturbance were independent of body condition, the needs-based strategy mitigated predicted reductions in provisioning by 10%-13%, while the ability-based strategy exaggerated reductions by 63%-113%. Lower WE availability resulted in more extreme outcomes because energy stores were smaller relative to the daily energy balance. In the 0% availability scenario, while the needs-based strategy reduced deaths by 100%, the ability-based strategy increased them by 335% relative to null and by 56% relative to the same strategy under the 5%-6.7% WE availability scenario. These results highlight that state-dependent disturbance responses and energy store availability could substantially impact the population consequences of disturbance. Our ability to set appropriate precautionary disturbance thresholds therefore requires empirical tests of ability- vs needs-based response modification as a function of body condition and a clearer understanding of energy store availability.

Consumption of juvenile chum salmon by a seabird species during early sea life

Juvenile mortality, a key factor determining the stock sizes of salmonids, may be increased by predation both in rivers and along shores. Information on predation at sea, however, is scarce. We analysed the diet of a pelagic seabird, the rhinoceros auklet Cerorhinca monocerata, breeding on an isolated island off eastern Hokkaido, Japan, and estimated their consumption of juvenile chum salmon Oncorhynchus keta. The auklets brought juvenile chum salmon and Japanese anchovy Engraulis japonicus for their chicks and, in addition, fed on squid themselves. The fork length of most of the juvenile chum salmon was over 80 mm, indicating that they were migrating to offshore nursery area, the Sea of Okhotsk. Using a simple bioenergetics model, the consumption of juvenile chum salmon by auklets during the first half of chick-rearing period (late June to middle July) was 316.6 t in 2014 (296.4 t by adults, 20.2 t by chicks) and 11.7 t in 2015 (0 t by adults, 11.7 t by chicks). The otoliths of six out of 66 juvenile salmon found in the diet for chicks had thermal markings and indicated that these fish were released from the rivers along Pacific coast of Hokkaido. Our study first demonstrates the extent of the auklets' consumption contributing to the reduction of the survival in the open coastal area of juvenile chum salmon with the known stock origins.

Climate Warming, Resource Availability, and the Metabolic Meltdown of Ectotherms.

Climate warming may lower environmental resource levels, growth, and fitness of many ectotherms. In a classic experiment, Brett and colleagues documented that growth rates of salmon depended strikingly on both temperature and food levels. Here we develop a simple bioenergetic model that explores how fixed temperatures and food jointly alter the thermal sensitivity of net energy gain. The model incorporates differing thermal sensitivities of energy intake and metabolism. In qualitative agreement with Brett's results, it predicts that decreased food intake reduces growth rates, lowers optimal temperatures for growth, and lowers the highest temperatures sustaining growth (upper thermal limit). Consequently, ectotherms facing reduced food intake in warm environments should restrict activity to times when low body temperatures are biophysically feasible, but-in a warming world-that will force ectotherms to shorten activity times and thus further reduce food intake. This "metabolic meltdown" is a consequence of declining energy intake coupled with accelerating metabolic costs at high temperatures and with warming-imposed restrictions on activity. Next, we extend the model to explore how increasing mean environmental temperatures alter the thermal sensitivity of growth: when food intake is reduced, optimal temperatures and upper thermal limits for growth are lowered. We discuss our model's key assumptions and caveats as well as its relationship to a recent model for phytoplankton. Both models illustrate that the deleterious impacts of climate warming on ectotherms will be amplified if food intake is also reduced, either because warming reduces standing food resources or because it restricts foraging time.

Activity seascapes highlight central place foraging strategies in marine predators that never stop swimming

BackgroundCentral place foragers (CPF) rest within a central place, and theory predicts that distance of patches from this central place sets the outer limits of the foraging arena. Many marine ectothermic predators behave like CPF animals, but never stop swimming, suggesting that predators will incur ‘travelling’ costs while resting. Currently, it is unknown how these CPF predators behave or how modulation of behavior contributes to daily energy budgets. We combine acoustic telemetry, multi-sensor loggers, and hidden Markov models (HMMs) to generate ‘activity seascapes’, which combine space use with patterns of activity, for reef sharks (blacktip reef and grey reef sharks) at an unfished Pacific atoll.ResultsSharks of both species occupied a central place during the day within deeper, cooler water where they were less active, and became more active over a larger area at night in shallower water. However, video cameras on two grey reef sharks revealed foraging attempts/success occurring throughout the day, and that multiple sharks were refuging in common areas. A simple bioenergetics model for grey reef sharks predicted that diel changes in energy expenditure are primarily driven by changes in swim speed and not body temperature.ConclusionsWe provide a new method for simultaneously visualizing diel space use and behavior in marine predators, which does not require the simultaneous measure of both from each animal. We show that blacktip and grey reef sharks behave as CPFs, with diel changes in activity, horizontal and vertical space use. However, aspects of their foraging behavior may differ from other predictions of traditional CPF models. In particular, for species that never stop swimming, patch foraging times may be unrelated to patch travel distance.

How can bioenergetics help us predict changes in fish growth patterns?

Individual growth rates are an important component of ecological processes and models. Understanding how and when growth rates may vary is necessary for predicting changes in size-specific rates like reproductive output, age at recruitment to fishing gear and even market prices. The von Bertalanffy growth function (VBGF) is the most common growth function used today. This model is integrated from a simple bioenergetics model; re-examining the link between von Bertalanffy growth and bioenergetics will help predict how environmental and demographic rates influence growth rates over time. In this paper, we discuss how a simple bioenergetics model can help predict density dependent growth and demonstrate how to incorporate environmental drivers into the VBGF based on the original bioenergetics model. Finally, we discuss difficulties and pitfalls in linking environmental and demographic variation to changes in growth.

Lesser black-backed gulls (Larus fuscus) consuming swimming crabs: An important link in the food web of the southern North Sea

Swimming crabs (Liocarcinus spp.) are one of the most common brachyuran species in the North Sea, and their abundance has substantially increased over the last century. Seabirds such as lesser black-backed gulls (LBBG) commonly feed mainly on higher-trophic-level organisms such as fish. However, intensive use of swimming crabs by LBBGs in the eastern North Sea has been noted over several years. Our investigation of this aspect of the food web by examining food remains from breeding LBBGs showed that swimming crabs accounted for more than half of the nutrition of LBBGs. Gulls selected larger individuals than expected, based on sizes of free-living swimming crabs. A long-term data set (2002–2006) shows that gulls took swimming crabs mainly in the early morning and late evening, suggesting that they might migrate vertically in the water column. Moreover, it shows that although swimming crabs occurred at considerable distances from the shore, LBBGs took this prey item exclusively from near the shore where it was most abundant. This suggests the existence of a possible energy threshold above which gulls experience a net energy loss, if they have to travel too far from their colony, where the abundance of swimming crabs is lower and the energy intake might thus not compensate for the long-distance flights. Swimming-crab abundance did not appear to be the primary factor influencing overall gull distribution. A simple bioenergetic model showed that the 22,000 individual LBBGs in the most important breeding colony in the south-eastern North Sea consumed approximately 35 million swimming crabs annually (i.e. 1590 swimming crabs per individual gull) during the breeding period. However, considering the high numbers of swimming crabs in the south-eastern North Sea (demonstrated by bottom-trawl surveys in 2005 and 2007) LBBGs are unlikely to exert top-down control on this prey. Conversely, a bottom-up effect is more likely, potentially enabling further increases in LBBG populations through increases in their most important prey item in the south-eastern North Sea.

Field data and growth model for mussels Mytilus edulis in Danish waters

Growth rates of blue mussels, Mytilus edulis, in suspended net-bags were measured in field experiments conducted in Limfjorden and Great Belt, Denmark, for extended periods of time (22–69 days) with up to 8 intermediate data samplings during the period. The resulting time series of growth of different overlapping size-classes of M. edulis were analysed individually and after being assembled to cover the full range of sizes, as full time series in terms of weight specific growth rate (µ=(1/W) dW/dt,% day−1) as a function of dry weight of soft parts (W, g). The results were compared to a simple bioenergetic growth model for mussels (µ=aW b , a=0.871×C−0.986, b=− 0.34), and observed power-law relations of growth data were in good agreement with the model, which takes into account the prevailing average chlorophyll a (chl a) concentration (C, µg chl a l−1) at field sites. Thus, the b-values of data were close to the predicted −0.34 while the a-value was in one case lower than estimated due to suboptimal conditions during part of the growth period. As a supplementary interpretation the growth data have been expressed in terms of the time to double the dry weight of soft parts for a given size of mussel and at a given experimental site.

Assessing the Potential for Salmon Recovery via Floodplain Restoration: A Multitrophic Level Comparison of Dredge-Mined to Reference Segments

Pre-restoration studies typically focus on physical habitat, rather than the food-base that supports aquatic species. However, both food and habitat are necessary to support the species that habitat restoration is frequently aimed at recovering. Here we evaluate if and how the productivity of the food-base that supports fish production is impaired in a dredge-mined floodplain within the Yankee Fork Salmon River (YFSR), Idaho (USA); a site where past restoration has occurred and where more has been proposed to help recover anadromous salmonids. Utilizing an ecosystem approach, we found that the dredged segment had comparable terrestrial leaf and invertebrate inputs, aquatic primary producer biomass, and production of aquatic invertebrates relative to five reference floodplains. Thus, the food-base in the dredged segment did not necessarily appear impaired. On the other hand, we observed that off-channel aquatic habitats were frequently important to productivity in reference floodplains, and the connection of these habitats in the dredged segment via previous restoration increased invertebrate productivity by 58%. However, using a simple bioenergetic model, we estimated that the invertebrate food-base was at least 4× larger than present demand for food by fish in dredged and reference segments. In the context of salmon recovery efforts, this observation questions whether additional food-base productivity provided by further habitat restoration would be warranted in the YFSR. Together, our findings highlight the importance of studies that assess the aquatic food-base, and emphasize the need for more robust ecosystem models that evaluate factors potentially limiting fish populations that are the target of restoration.

The diet of Atlantic Yellow-legged Gulls (Larus michahellis atlantis) at an oceanic seabird colony: estimating predatory impact upon breeding petrels

The diet and breeding ecology of Yellow-legged Gulls (Larus michahellis atlantis) were studied on Selvagem Grande, North Atlantic in the nesting season of 2007. We collected and analyzed 715 pellets from adults. The most frequent prey were White-faced Storm-petrels (Pelagodroma marina; present on 40.8% of all pellets) and the endemic land snails (Theba macandrewiana; present on 36.5% of all pellets). Other birds, namely Cory’s Shearwaters (Calonectris diomedea), Macaronesian Shearwaters (Puffinus assimilis), Bulwer’s Petrels (Bulweria bulwerii), and Band-rumped Storm-petrels (Oceanodroma castro) were relatively less frequent, but overall, seabirds were present in ca. 50% of all pellets, representing an estimated 60.4% of all mass consumed by gulls. We estimate that the contribution of seabirds to the overall caloric balance accounted for 82.5% of all energy consumed. The number of gull pairs breeding on Selvagem Grande was 12 on 2005 and 2007. Breeding success was low (0.92 and 0.25 juveniles per breeding pair, respectively). Using a simple bioenergetics model, we estimate the breeding gull population to have the potential to consume approximately 4,847 adult/sub-adult seabirds in 3.5 months in order to meet its energetic requirements. The importance of the estimated predation levels is discussed and some management actions are suggested.

Size-dependent thermal preferences in a pelagic fish

Large fish often inhabit colder waters than small fish. Using a simple bioenergetic model, we found that the optimal temperature for growth should decrease with increasing body size. We predicted that this mechanism would produce an ontogenetic change in thermal preference and then tested our predictions with Pacific salmon, Oncorhynchus spp. In a laboratory experiment, the slope of a regression of growth increment on initial size became steeper with increasing temperature, so that the optimal temperature for growth decreased with increasing body size. In field observations, larger and older salmon inhabited cooler areas, whereas smaller and younger salmon inhabited warmer areas. These patterns were consistent with a size-dependent effect of temperature on condition factor, a parameter shown experimentally to be a measure of the most recent growth performance. Temperatures for maximising condition factor were lower for larger fish. Thus, an ontogenetic change in individual thermal preference toward cooler areas maximises the growth performance of fish, and the negative effects of climate warming on growth are hypothesised to be more severe for larger fish.

The diet of feral cats at New Island, Falkland Islands, and impact on breeding seabirds

We studied the diet of feral cats (Felis catus) on New Island, Falkland Islands, through the analysis of 373 scats collected during the austral summers of 2004/2005 and 2005/2006. The most frequent prey were three introduced mammals (house mice Mus musculus, ship rats Rattus rattus and rabbits Sylvilagus sp.) and the thin-billed prion Pachyptila belcheri (each season present on ca. 21% of the analysed scats). These represent the first systematic data on feral cat diet for the Falklands. A simple bioenergetics model suggests that cats could be eating in the region of 1,500–11,000 prions per season, representing <1% of the local adult and subadult population. Predation on other seabirds nesting on New Island (several penguin species, albatrosses and cormorants) was unimportant, with the possible exception of white-chinned petrels Procellaria aequinoctialis, which nest locally in very small numbers. For each prion eaten, cats were estimated to have killed 1.1–1.9 ship rats during the summer season, and probably more in autumn and winter. Knowing that ship rats are prion predators, it is conceivable that, on the whole, cats are having a positive impact on the prion population, a scenario predicted by general theoretical models. Thus, considering the available information, we would not recommend the implementation of any eradication programme on New Island that would target cats in isolation. Nevertheless, it would be prudent to consider some local action targeting cats and rats around the small New Island white-chinned petrel colony.

Migration supports uneven consumer control in a sewage‐enriched river food web

Summary We studied the response of the St Lawrence River food web to enrichment by primary‐treated sewage from the city of Montreal, Canada. Despite the richness and complexity of this food web, the openness of the system and the limited production possible in this temperate river's short growing season, we found that biomass densities of consumers responded to enrichment according to the qualitative predictions of a simple bioenergetic model. All consumer trophic levels responded to sewage enrichment, but not all members of each trophic level: top piscivores seemed to control small, benthivorous fish but were unable to control larger fish, so the intermediate consumer level became dominated by Catastomidae (suckers). Consequently, the epiphytic prey of small fish were free to respond to sewage enrichment, but the benthic prey of suckers were not. The important elements of complexity seemed to be the factors that determine the realized pattern of feeding linkages: heterogeneity in prey vulnerability (predator–prey size ratios) and predator efficiency (vegetation cover for ambush predators, inaccessibility of epiphytic prey to bottom‐feeding suckers). Because of the openness of the system, the community was able to respond to enrichment by a combination of demographic (production) and behavioural (migration) mechanisms. We argue that the food web model described an energetically favourable state, and that migration provided a ‘shortcut’ for the system to approach this state within a short growing season.

Significance of nocturnal purse seine fisheries for seabirds: a case study off the Ebro Delta (NW Mediterranean)

Seabirds are known to make extensive use of fishery waste, a phenomenon that has been particularly well studied in relation to demersal fisheries, especially when operatingduringdaylig ht hours. Contrarily, very little is known about the importance of predominantly nocturnal fisheries in providingfeedingopportunities to seabirds. We considered the particular case of purse se- iningfor small pelagic fish, which takes place basically at night, and assessed the significance of this fishing practice for seabirds off the Ebro Delta (NW Mediterranean). Fieldwork was conducted on board commercial purse seiners (nocturnal activity) in 1997-1998, and was com- plemented with observations performed on board both commercial bottom trawlers (diurnal activity; 1997- 1998) and a research vessel (1999-2000). The purse seine fleet targets small clupeoids, which are attracted and concentrated by the light of a powerful lamp, and then captured usingan encirclingnet. Purse seiners frequently changed fishing area, took very variable catches, and were strongly influenced by the weather. This made the fishery unattractive to most seabird species, which primarily at- tended purse seiners duringthe discardingprocess. This process took place on the way back to port after dawn (i.e. with daylight) during daylight and was quite irregu- lar, thus attractinglower numbers of seabirds than did trawlers. The threatened Audouin's gull Larus audouinii was the only species attendingpurse seiners reg ularly at night, capturing live fish concentrated at the sea surface duringthe haulingprocess. This is in accordance with the specialisation of this gull in the capture of epipelagic fish at night, which seems facilitated by purse seiners. Indeed, the vessels would favour the direct capture of fish (illu- mination of the sea surface, concentration of the fish), as well as the location of the shoals (light signalling). The purse seiningfishery was especially important for Aud- ouin's gull during trawling moratoria (when trawling discards were not available) and in the non-breeding season. A simple bioenergetic model estimated that in- dividual Audouin's gulls could obtain a mean of 669 kJ haul -1 , which would represent far more than half of the daily energy requirements of breeding birds. Provided that Audouin's gulls feeding in a given area could attend more than one haul in a short time, birds attendingpurse seiners at night could easily meet their energy require- ments. However, there was strongvariability in our esti- mate (from 0 to 1659 kJ bird -1 haul -1 , 95% CI), and feedingat purse seiners would only sometimes be profit- able for Audouin's gulls. Purse seine fisheries could be of importance for other nocturnal seabirds in other regions such as the SE Pacific, and this deserves further research. It is important to note that purse seiners could also be detrimental for many seabirds, through direct competi- tion and eventual depletion of fish stocks.

Local temperature changes and human skeletal muscle metabolism.

The aim of this review is to describe the effects induced by local temperature changes on human skeletal muscle metabolism. More specifically, we will consider the influence of temperature on the mechanical properties of muscle contraction, on aerobic metabolism, anaerobic metabolism and on the Lohmann reaction. The text has been voluntarily organized on the basis of a simple bioenergetic model describing the different energy fluxes appearing in the muscle system. This approach should better highlight some of the points that still need to be investigated. Although it was not always possible to restrict the discussion to human muscle, the references report mainly data obtained directly on humans or on isolated human fibres. A short comment on skeletal muscle temperature measurement techniques, on humans, is also included.

An energetic evaluation of a predator–prey (leech–amphipod) couple in Montezuma Well, Arizona, USA

1. The highly stable conditions in Montezuma Well, Arizona, have contributed to a very close predator–prey relationship between the endemic leech, Erpobdella montezuma, and its endemic amphipod prey, Hyalella montezuma, which forms nearly 90% of the leech diet. 2. Using a simple bioenergetic model, it was determined why a benthic opportunistic foraging strategy, typical of most other erpobdellids, is inferior to the specialized foraging behaviour utilized by E. montezuma and why reproduction by the leech is restricted during certain times of the year. 3. Our model demonstrated that to attain a biomass in excess of 2000 mg (maximum field size) during periods of low amphipod densities in the winter E. montezuma must feed on alternative prey types and have a foraging activity &lt; 4 h per day. 4. Leech reproduction 4–6 months prior to the onset of winter food shortages of prey increases juvenile and adult survivorship with highest reproductive success for E. montezuma occurring in June–July. 5. Rather than being an obligate forager on H. montezuma, E. montezuma exploits a periodically abundant amphipod during most of the year in addition to alternate prey types during the winter thereby achieving an overall higher rate of energy gain than could be achievable by other closely related species of erpobdellids utilizing an opportunistic foraging approach.

Modelling the Ecological Constraints on Growth and Movement of Juvenile American Shad (Alosa sapidissima) in the Hudson River Estuary

Juvenile fishes often face conditions that force them to experience fitness trade-offs (e.g., foregoing a rich food patch because of high risk of predation). In this study, three aspects of the environment of juvenile American shad: food availability, predation risk, and “thermal risk” (defined here as the probability of the onset of adverse temperatures; ≤9°C, the temperature at which feeding ceases), are evaluated empirically with data from the Hudson River estuary in New York State. The evaluations are then used in dynamic programming models to determine when juvenile American shad should switch habitat (upper versus middle versus lower estuary), and, in combination with a simple bioenergetic model, to determine growth trajectories for fish spawned at different times in the spawning season. Comparisons of simulations with real data suggest that scenarios in which predation risk is highest in the lower river produce the most realistic patterns of habitat use. High upriver food availability in June promotes use of the upriver habitat; however, by September most size classes of fish utilize the middle estuary, and by late October, fish move to the lower estuary (even in the face of higher predation risk), due to a combination of lower food resources and thermal risks in the upper and middle estuary.

An estimate of the quantity of squid consumed by seabirds in the eastern North Atlantic and adjoining seas

A simple bioenergetics model provided estimates of annual squid consumption by seabirds as 40 000 t in the NE North Atlantic, 63 000 t in the SE North Atlantic and 3000 t in the Mediterranean. Squid was estimated to represent only 1% (by mass) of the diet of seabirds in the NE North Atlantic but 16% of the diet of seabirds in the SE North Atlantic. Main consumers of squid were fulmar and Manx shearwater in the NE and Cory's shearwater in the SE and Mediterranean. In general, procellariiforms tended to be the major seabird consumers of squid in all parts of the world. In comparison with studies in the Pacific and in the southern hemisphere (466 000 t of squid eaten by seabirds at south Georgia and 223 000 t of squid represent 54% of seabird diet at Hawaii), squid formed a notably small part of the diet of NE North Atlantic seabirds. Comparisons between diets of the same species in west and east Atlantic populations also showed less squid in NE North Atlantic seabird diets, suggesting that this may be at least in part a result of differences in prey availability.

Bioenergetics of the bull shark, Carcharhinus leucas, maintained in captivity

AbstractUnderstanding the energy requirements for captive sharks is important for their successful long‐term maintenance. This information is critical in assessing the health of the animals and the suitability of their environment. We studied five bull sharks (Carcharhinus leucas) for up to 7 years in a 2.5 × 106 liter oceanarium. Individual animal feedings provided information for food intake analysis. During the first 3 years, fork length increase was estimated to have averaged 1.9 cm/month (s.d. = 0.1), or 23.0 cm/year. Biannual measurements, begun in the fourth year, showed that growth rates decreased during the next 4 years to a mean rate of 0.6 cm/month (s.d. = 0.2), or about 7.0 cm/year. Mean food consumption from June 1988 to December 1992 was 3.4% body weight per week. Caloric conversion of weights incorporated into a simple bioenergetics model providing mean metabolic expenditures per animal was 5.7 (s.d. = 0.3) and 4 (s.d. = 0.5) kcal/kg/day for 1991 and 1992, respectively. © 1994 Wiley‐Liss, Inc.