Empirical standard mass equation for Salmo marmoratus

Total length (L_T) (range 24–1000 mm; mean ±s.e . = 170·21 ± 0·36 mm) and mass (W) (range 0·10–9590 g; mean ±s.e . = 76·03 ± 0·87 g) of 36 460 specimens of marble trout Salmo marmoratus were used to compute a standard mass (W_s) equation for this species by means of the empirical percentile (EmP) method. The EmP W_s equation calculated was: log₁₀W_s = ?5·208 + 3·202 log₁₀L_T? 0·046 (log₁₀L_T)² (L_T range 90–570 mm) and it is valid throughout the species' area of distribution across Europe.     

Geographic variation in density-dependent dynamics impacts the synchronizing effect of dispersal and regional stochasticity

Explanations for the ubiquitous presence of spatially synchronous population dynamics have assumed that density-dependent processes governing the dynamics of local populations are identical among disjunct populations, and low levels of dispersal or small amounts of regionalized stochasticity (Moran effect) can act to synchronize populations. In this study we used historical spatially referenced data on gypsy moth (Lymantria dispar) outbreaks to document that density-dependent processes can vary substantially across geographical landscapes. This variation may be due in part to geographical variation in habitat (e.g., variation in forest composition). We then used a second-order log-linear stochastic model to explore how inter-population variation in density-dependent processes affects synchronization via either synchronous stochastic forcing or dispersal. We found that geographical variation in direct density-dependence (first order) greatly diminishes synchrony caused by stochasticity but only slightly decreases synchronization via dispersal. Variation in delayed density-dependence (second order) diluted synchrony caused by regional stochasticity to a lesser extent than first-order variation, but it did not have any influence on synchrony caused by dispersal. In general, synchronization caused by dispersal was primarily dependent upon the instability of populations and only weakly, if at all, affected by similarities in density-dependence among populations. We conclude that studies of synchrony should carefully consider both the nature of the synchronizing agents and the pattern of local density-dependent processes, including how these vary geographically.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Thermal time and ecological strategies - a unifying hypothesis

Rates of embryogenesis and of development and growth in several nematodes are linearly related to temperature over a considerable range. On this basis, published data on the thermal time requirements are compared for a tropical and a temperate species of plant parasitic nematode Meloidogyne javanica and M. hapla respectively, the two being closely related and morphologically and biologically similar. M. hapla has a lower base temperature (T_b) and a higher thermal constant (S) than M. javanica with the relative values being almost inversed. Consequently, above their respective T_b values the slope of the relationship between rate of development and temperature was greater for the tropical species than that for the temperate species. A mathematical exploration of the relationship between T_b and S was made assuming that, over a narrow range, T_b×S was a constant. With this assumption, for any given average environmental temperature (T_e) the optimum base temperature for minimum developmental duration was T_e/2, and the temperature at which the duration of development was equal for the otherwise identical species was shown to be the sum of their base temperatures. The practical effect of the differences in T_b and S was to give M. hapla, the temperate species, a shorter life cycle and hence a competitive advantage at temperatures below 21ÅC and M. javanica, the tropical species, the advantage above that temperature. It is argued that a negative correlation between T_b and S is likely to be widespread, and provides a mechanism for regulating the distributions of related, competing organisms. Support for the hypothesis that the value of S tends to decrease as T_b increases is derived from data on the embryogenesis of an animal parasitic nematode Haemonchus contortus and from seed germination studies. Contrary results and exceptions are also briefly discussed. The observed interaction between T_b and S may be fundamental to many poikilothermic organisms and plants and provides an explanation for tropical species generally having higher T_b values than temperate ones. The ecological implications of different values of T_b and of S, including their relationship with organisms which are “r” or “K” strategists are briefly discussed.     

Light Masking in the Field: An Experiment with Nocturnal and Diurnal Spiny Mice Under Semi-natural Field Conditions

Light masking has been studied almost exclusively in the laboratory. The authors populated four field enclosures with locally coexisting nocturnal Acomys cahirinus and diurnal A. russatus, and monitored their body temperatures (T_b) using implanted temperature-sensitive radio transmitters. A 3-h light pulse was initiated at the beginning of two consecutive nights; preceding nights were controls. A. cahirinus T_b and calculated activity levels decreased significantly during the light pulse, demonstrating a negative light masking response (light effect on T_b: ?0.32°C?±?0.15°C; average calculated activity records during the light pulse: 7?±?1.53, control: 9.8?±?1.62). Diurnal A. russatus did not respond to the light pulse. We conclude that light masking is not an artifact of laboratory conditions but represents a natural adaptive response in free-living populations. (Author correspondence: Shayroti@post.tau.ac.il)     

Torpor and thermal energetics in a tiny Australian vespertilionid,the little forest bat (<Emphasis Type="Italic">Vespadelus vulturnus</Emphasis>)

Data on thermal energetics for vespertilionid bats are under-represented in the literature relative to their abundance, as are data for bats of very small body mass. Therefore, we studied torpor use and thermal energetics in one of the smallest (4 g) Australian vespertilionids, Vespadelus vulturnus. We used open-flow respirometry to quantify temporal patterns of torpor use, upper and lower critical temperatures (T _uc and T _lc) of the thermoneutral zone (TNZ), basal metabolic rate (BMR), resting metabolic rate (RMR), torpid metabolic rate (TMR), and wet thermal conductance (C _wet) over a range of ambient temperatures (T _a). We also measured body temperature (T _b) during torpor and normothermia. Bats showed a high proclivity for torpor and typically aroused only for brief periods. The TNZ ranged from 27.6°C to 33.3°C. Within the TNZ T _b was 33.3±0.4°C and BMR was 1.02±0.29 mlO₂ g⁻¹ h⁻¹ (5.60±1.65 mW g⁻¹) at a mean body mass of 4.0±0.69 g, which is 55 % of that predicted for a 4 g bat. Minimum TMR of torpid bats was 0.014±0.006 mlO₂ g⁻¹ h⁻¹ (0.079±0.032 mW g⁻¹) at T _a=4.6±0.4°C and T _b=7.5±1.9. T _lc and C _wet of normothermic bats were both lower than that predicted for a 4 g bat, which indicates that V. vulturnus is adapted to minimising heat loss at low T _a. Our findings support the hypothesis that vespertilionid bats have evolved energy-conserving physiological traits, such as low BMR and proclivity for torpor.     

Density-dependent dispersal and spatial population dynamics

The synchronization of the dynamics of spatially subdivided populations is of both fundamental and applied interest in population biology. Based on theoretical studies, dispersal movements have been inferred to be one of the most general causes of population synchrony, yet no empirical study has mapped distance-dependent estimates of movement rates on the actual pattern of synchrony in species that are known to exhibit population synchrony. Northern vole and lemming species are particularly well-known for their spatially synchronized population dynamics. Here, we use results from an experimental study to demonstrate that tundra vole dispersal movements did not act to synchronize population dynamics in fragmented habitats. In contrast to the constant dispersal rate assumed in earlier theoretical studies, the tundra vole, and many other species, exhibit negative density-dependent dispersal. Simulations of a simple mathematical model, parametrized on the basis of our experimental data, verify the empirical results, namely that the observed negative density-dependent dispersal did not have a significant synchronizing effect.     

Winter body temperature patterns in free-ranging Cape ground squirrel, Xerus inauris: no evidence for torpor

The body temperature (T _b) of Cape ground squirrels (Xerus inauris, Sciuridae) living in their natural environment during winter has not yet been investigated. In this study we measured abdominal T _b of eight free-ranging Cape ground squirrels over 27 consecutive days during the austral winter. Mean daily T _b was relatively stable at 37.0 ± 0.2°C (range 33.4 to 40.2°C) despite a marked variation in globe temperature (T _g) (range −7 to 37°C). Lactating females (n = 2) consistently had a significantly higher mean T _b (0.7°C) than non-lactating females (n = 3) and males. There was a pronounced nychthemeral rhythm with a mean active phase T _b of 38.1 ± 0.1°C and a mean inactive phase T _b of 36.3 ± 0.3°C for non-lactating individuals. Mean daily amplitude of T _b rhythm was 3.8 ± 0.2°C. T _b during the active phase closely followed T _g and mean active phase T _b was significantly correlated with mean active phase T _g (r ² = 0.3–0.9; P < 0.01). There was no evidence for daily torpor or pronounced hypothermia during the inactive phase, and mean minimum inactive phase T _b was 35.7 ± 0.3°C for non-lactating individuals. Several alternatives (including nocturnal huddling, an aseasonal breeding pattern and abundant winter food resources) as to why Cape ground squirrels do not employ nocturnal hypothermia are discussed.     

Climatic drivers of pinyon mouse Peromyscus truei population dynamics in a resource-restricted environment

Highly variable patterns in temperature and rainfall events can have pronounced consequences for small mammals in resource-restricted environments. Climatic factors can therefore play a crucial role in determining the fates of small mammal populations. We applied Pradel's temporal symmetry model to a 21-year capture–recapture dataset to study population dynamics of the pinyon mouse (Peromyscus truei) in a semi-arid mixed oak woodland in California, USA. We examined time-, season- and sex-specific variation in realized population growth rate (λ) and its constituent vital rates, apparent survival and recruitment. We also tested the influence of climatic factors on these rates. Overall monthly apparent survival was 0.81 ± 0.004 (estimate ± SE). Survival was generally higher during wetter months (October–May) but varied over time. Monthly recruitment rate was 0.18 ± 0.01, ranging from 0.07 ± 0.01 to 0.63 ± 0.07. Although population growth rate (λ) was highly variable, overall monthly growth rate was close to 1.0, indicating a stable population during the study period (λ ± SE = 0.99 ± 0.01). Average temperature and its variability negatively affected survival, whereas rainfall positively influenced survival and recruitment rates, and thus the population growth rate. Our results suggest that seasonal rainfall and variation in temperature at the local scale, rather than regional climatic patterns, more strongly affected vital rates in this population. Discerning such linkages between species' population dynamics and environmental variability are critical for understanding local and regional impacts of global climate change, and for gauging viability and resilience of populations in resource-restricted environments.     

Daily torpor in the gray mouse lemur (Microcebus murinus) in Madagascar: energetic consequences and biological significance

Patterns and energetic consequences of spontaneous daily torpor were measured in the gray mouse lemur (Microcebus murinus) under natural conditions of ambient temperature and photoperiod in a dry deciduous forest in western Madagascar. Over a period of two consecutive dry seasons, oxygen consumption (VO₂) and body temperature (T _b) were measured on ten individuals kept in outdoor enclosures. In all animals, spontaneous daily torpor occurred on a daily basis with torpor bouts lasting from 3.6 to 17.6 h, with a mean torpor bout duration of 9.3 h. On average, body temperatures in torpor were 17.3±4.9°C with a recorded minimum value of 7.8°C. Torpor was not restricted to the mouse lemurs’ diurnal resting phase: entries occurred throughout the night and arousals mainly around midday, coinciding with the daily ambient temperature maximum. Arousal from torpor was a two-phase process with a first passive, exogenous heating where the T _b of animals increased from the torpor T _b minimum to a mean value of 27.1°C before the second, endogenous heat production commenced to further raise T _b to normothermic values. Metabolic rate during torpor (28.6±13.2 ml O₂ h^–1) was significantly reduced by about 76% compared to resting metabolic rate (132.6±50.5 ml O₂ h^–1). On average, for all M. murinus individuals measured, hypometabolism during daily torpor reduced daily energy expenditure by about 38%. In conclusion, all these energy-conserving mechanisms of the nocturnal mouse lemurs, with passive exogenous heating during arousal from torpor, low minimum torpor T _bs, and extended torpor bouts into the activity phase, comprise an important and highly adapted mechanism to minimize energetic costs in response to unfavorable environmental conditions and may play a crucial role for individual fitness. Received: 8 July 1999 / Accepted: 3 December 1999     

Effects of patch number and dispersal patterns on population dynamics and synchrony

In this paper, we examine the effects of patch number and different dispersal patterns on dynamics of local populations and on the level of synchrony between them. Local population renewal is governed by the Ricker model and we also consider asymmetrical dispersal as well as the presence of environmental heterogeneity. Our results show that both population dynamics and the level of synchrony differ markedly between two and a larger number of local populations. For two patches different dispersal rules give very versatile dynamics. However, for a larger number of local populations the dynamics are similar irrespective of the dispersal rule. For example, for the parameter values yielding stable or periodic dynamics in a single population, the dynamics do not change when the patches are coupled with dispersal. High intensity of dispersal does not guarantee synchrony between local populations. The level of synchrony depends also on dispersal rule, the number of local populations, and the intrinsic rate of increase. In our study, the effects of density-independent and density-dependent dispersal rules do not show any consistent difference. The results call for caution when drawing general conclusions from models of only two interacting populations and question the applicability of a large number of theoretical papers dealing with two local populations.     

Thermal ecology of the Australian agamid Pogona barbata

This study compares the thermal ecology of male bearded dragon lizards (Pogona barbata) from south-east Queensland across two seasons: summer (1994–1995) and autumn (1995). Seasonal patterns of body temperature (T _b) were explored in terms of changes in the physical properties of the thermal environment and thermoregulatory effort. To quantify thermoregulatory effort, we compared behavioral and physiological variables recorded for observed lizards with those estimated for a thermoconforming lizard. The study lizards' field T _bs varied seasonally (summer: grand daily mean (GDM) 34.6 ± 0.6°C, autumn: GDM 27.5 ± 0.3°C) as did maximum and minimum available operative temperatures (summer: GDM T _max 42.1 ± 1.7°C, T _min 32.2 ± 1.0°C, autumn: GDM T _max 31.7 ± 1.2°C, T _min 26.4 ± 0.5°C). Interestingly, the range of temperatures that lizards selected in a gradient (selected range) did not change seasonally. However, P. barbata thermoregulated more extensively and more accurately in summer than in autumn; lizards generally displayed behaviors affecting heat load nonrandomly in summer and randomly in autumn, leading to the GDM of the mean deviations of lizards' field T _bs from their selected ranges being only 2.1 ± 0.5°C in summer, compared to 4.4 ± 0.5°C in autumn. This seasonal difference was not a consequence of different heat availability in the two seasons, because the seasonally available ranges of operative temperatures rarely precluded lizards from attaining field T _bs within their selected range, should that have been the goal. Rather, thermal microhabitat distribution and social behavior appear to have had an important influence on seasonal levels of thermoregulatory effort. Received: 28 April 1997 / Accepted: 29 December 1997     

The extrasplanchnic origin of blood dihydrotestosterone in elderly men

The splanchnic extraction and interconversion of testosterone (T) and dihydrotestosterone (DHT) were studied in 5 elderly men undergoing cardiac catheterization using a constant Infusion of [1,2-³H] testosterone and [4-¹⁴C] DHT. Metabolic clearance rate (MCR), splanchnic extraction (SE), splanchnic clearance (SC), extrasplanchnic clearance (ESC), transfer constant In blood ([P]_BB^T-DHT) and transfer constant across the liver ([P]_BB^T-DHT) were calc?ulated. The MCR^T was 675 ± 108 (mean ± SC) L/day and MCR^DHT was 409 ± 68 L/day. SE^T was 45.9 ± 7.0% and SE^DHT was 18.5 ± 5.4%. When these values are compared with those recently reported by us for normal men, there is a $\text{1}\text{3}$ reduction in SE^T and $\text{1}\text{2}$ reduction for SE^DHT in elderly men. The calculated SC^T and ESC^T were 355 ± 72 L/day and 320 ± 86 L/day, respectively. SC^DHT and ESC^DHT were 145 + 48 L/day and 263 ± 77 L/day respectively, suggesting that a major fraction of DHT is metabolized in extrasplanchnic organs. No evidence for a net appearance of DHT by either mass or specific activity analysis in hepatic vein blood was observed indicating that the splanchnic compartment does not contribute DHT into the circulation either by $\text{de novp}$ synthesis or via conversion from testosterone. This work indicates that conversion of testosterone to DHT in elderly men occurs entirely in extrasplanchnic tissue.     

Life‐stage differences in spatial genetic structure in an irruptive forest insect: implications for dispersal and spatial synchrony

Dispersal determines the flux of individuals, energy and information and is therefore a key determinant of ecological and evolutionary dynamics. Yet, it remains difficult to quantify its importance relative to other factors. This is particularly true in cyclic populations in which demography, drift and dispersal contribute to spatio‐temporal variability in genetic structure. Improved understanding of how dispersal influences spatial genetic structure is needed to disentangle the multiple processes that give rise to spatial synchrony in irruptive species. In this study, we examined spatial genetic structure in an economically important irruptive forest insect, the spruce budworm (Choristoneura fumiferana) to better characterize how dispersal, demography and ecological context interact to influence spatial synchrony in a localized outbreak. We characterized spatial variation in microsatellite allele frequencies using 231 individuals and seven geographic locations. We show that (i) gene flow among populations is likely very high (F_st ≈ 0); (ii) despite an overall low level of genetic structure, important differences exist between adult (moth) and juvenile (larvae) life stages; and (iii) the localized outbreak is the likely source of moths captured elsewhere in our study area. This study demonstrates the potential of using molecular methods to distinguish residents from migrants and for understanding how dispersal contributes to spatial synchronization. In irruptive populations, the strength of genetic structure depends on the timing of data collection (e.g. trough vs. peak), location and dispersal. Taking into account this ecological context allows us to make more general characterizations of how dispersal can affect spatial synchrony in irruptive populations.     

Implications of climate change on the habitat shifts of tropical lizards

The effect of temperature on the distributions of ectothermic vertebrates is well documented. Despite the increase of 6°C expected in the next 60 years in South America, numerous vertebrates are still considered as ‘Least Concern’ species by the IUCN due to their large distribution, insufficient widespread threats and insignificant population decline. One example is the lizard Tropidurus torquatus (Squamata: Tropiduridae), commonly found thermoregulating in anthropic environments throughout the Brazilian Cerrado, but restricted to gallery forests in the equator‐ward localities. The urban areas in this warmer region have been colonised by other closely related congeners (e.g. Tropidurus oreadicus). This study aimed to understand this divergence of habitat selection by these tropirudids that may explain some of the species responses to past and future climate warming. We collected body temperatures (T_b), micro‐environmental temperatures (T_a) and operative (T_e) temperatures in four sites along a latitudinal gradient: a pole‐ward and two central sites where T. torquatus inhabit urban areas and one equator‐ward site where T. torquatus and T. oreadicus occur in the gallery forest and in urban microhabitats, respectively. All three populations of T. torquatus present similar T_b (35.5–36°C) and shared microhabitats with a similar T_a (34–37.3°C). The T_e in the equator‐ward urban site was considerably higher than in the gallery forest. Tropidurus oreadicus T_b was 38.2 °C (30.1–41.3°C) and was active at a T_a of 30.5–42.3°C. The overlap between the genus T_b, T_a and T_e highlights a decrease in the hours of activity that lizards would experience under climate warming. The reduction of hours of activity together with the devastation of natural habitats represents threats and an alarming scenario especially for the equator‐ward populations.     

Dehydration,with and without heat,in kangaroos from mesic and arid habitats: different thermal responses including varying patterns in heterothermy in the field and laboratory

Field data showing the daily patterns in body temperature (T _b) of kangaroos in hot, arid conditions, with and without water, indicate the use of adaptive heterothermy, i.e. large variation in T _b. However, daily T _b variation was greater in the Eastern Grey Kangaroo (Macropus giganteus), a species of mesic origin, than in the desert-adapted Red Kangaroo (Macropus rufus). The nature of such responses was studied by an examination of their thermal adjustments to dehydration in thermoneutral temperatures (25°C) and at high temperature (45°C) via the use of tame, habituated animals in a climate chamber. At the same level of dehydration M. rufus was less impacted, in that its T _b changed less than that for M. giganteus while it evaporated significantly less water. At a T _a of 45°C with water restriction T _b reached 38.9 ± 0.3°C in M. rufus compared with 40.2 ± 0.4°C for M. giganteus. The ability of M. rufus to reduce dry conductance in the heat while dehydrated was central to its superior thermal control. While M. giganteus showed more heterothermy, i.e. its T _b varied more, this seemed due to a lower tolerance of dehydration in concert with a strong thermal challenge. The benefits of heterothermy to M. giganteus were also limited because of thermal (Q₁₀) effects on metabolic heat production and evaporative heat loss. The impacts of T _b on heat production were such that low morning T _b’s seen in the field may be associated with energy saving, as well as water saving. Kangaroos respond to dehydration and heat similarly to many ungulates, and it is apparent that the accepted notions about adaptive heterothermy in large desert mammals may need revisiting.     

Determination of DNA base compositions from melting profiles in dilute buffers

Equations were determined for the dependency of the melting temperature (T_m) of DNA upon the logarithm of the sodium ion concentration, for four DNA samples of widely different base compositions (θ_GC). The slopes of these T_m versus log M equations wore found to decrease with increasing θ_{G C}of the samples. An empirical equation relating T_m, log M (Na⁺) and θ_{G C} was derived, which also accounts for differences in T_m versus log M slopes. Data from the literature for some synthetic polynucleotides and for the crab(Cancer pagarus) satellite poly AT are discussed in relation to the above finding. The changes in T_m versus log M slopes with θ_{G C} are interpreted in terms of changes in the thermodynamic parameters ΔS and ΔH with base composition.     

Patterns and dynamics of rest-phase hypothermia in wild and captive blue tits during winter

We evaluated biotic and abiotic predictors of rest-phase hypothermia in wintering blue tits (Cyanistes caeruleus) and also assessed how food availability influences nightly thermoregulation. On any given night, captive blue tits (with unrestricted access to food) remained largely homeothermic, whereas free-ranging birds decreased their body temperature (T _b) by about 5°C. This was not an effect of increased stress in the aviary as we found no difference in circulating corticosterone between groups. Nocturnal T _b in free-ranging birds varied with ambient temperature, date and time. Conversely, T _b in captive birds could not be explained by climatic or temporal factors, but differed slightly between the sexes. We argue that the degree of hypothermia is controlled predominantly by birds’ ability to obtain sufficient energy reserves during the day. However, environmental factors became increasingly important for thermoregulation when resources were limited. Moreover, as birds did not enter hypothermia in captivity when food was abundant, we suggest that this strategy has associated costs and hence is avoided whenever resource levels permit.     

Population synchrony in small-world networks

Network topography ranges from regular graphs (linkage between nearest neighbours only) via small-world graphs (some random connections between nodes) to completely random graphs. Small-world linkage is seen as a revolutionary architecture for a wide range of social, physical and biological networks, and has been shown to increase synchrony between oscillating subunits. We study small-world topographies in a novel context: dispersal linkage between spatially structured populations across a range of population models. Regular dispersal between population patches interacting with density-dependent renewal provides one ecological explanation for the large-scale synchrony seen in the temporal fluctuations of many species, for example, lynx populations in North America, voles in Fennoscandia and grouse in the UK. Introducing a small-world dispersal kernel leads to a clear reduction in synchrony with both increasing dispersal rate and small-world dispersal probability across a variety of biological scenarios. Synchrony is also reduced when populations are affected by globally correlated noise. We discuss ecological implications of small-world dispersal in the frame of spatial synchrony in population fluctuations.     

Thermoregulation as a limit to habitat use in alpine marmots (Marmota marmota)

Summary The body temperature (T _b) of free-living alpine marmots rose with activity; the higher the effective environmental temperature (T _e), the higher the rise. Maximum T _bof 40° C was reached at the time of greatest activity in late afternoon or evening. The activity pattern was strongly influenced by the microclimate. Up to an T _eof 25° C the animals spent more time above ground and were more active the higher T _ewas, but above 25° C this trend was reversed, and the animals withdrew increasingly into their burrows. On warm days the activity pattern was therefore bimodal and above ground presence was reduced, in contrast to cool days. Hence behavioural thermoregulation limits the available time for above ground activity on days with high T _ein this strictly diurnal species. We suggest that the alpine marmots' preference for south oriented slopes is due to the better conditions for hibernation there, the microclimate during summer is more favourable on northerly slopes. Thermoregulatory constraints could also keep alpine marmots away from lower elevations.     

Comparison of the prolonged swimming performances of closely related, morphologically distinct three‐spined sticklebacks Gasterosteus spp.

Prolonged swimming performances of two as yet unnamed species of three‐spined stickleback, Gasterosteus spp., were compared. The two fishes (not yet formally described, referred to here as benthic and limnetic) inhabit different niches within Paxton Lake, Texada Island, British Columbia, Canada, and are recent, morphologically distinct species. Limnetics had longer endurance during prolonged swimming than did benthics. The mean regression of the log₁₀ of fatigue time (F_t, s) on swimming speed (U, standard length, L_S s^?1) for limnetics (log₁₀F_t = 7·03 ? 0·46U) had a similar slope, but a significantly higher intercept than that for benthics (log₁₀F_t = 5·55 ? 0·43U). Adult benthics were larger, heavier and deeper‐bodied fish than limnetics. Limnetics, however, had a significantly greater pectoral fin edge:base ratio (mean ± s .e .: limnetics, 4·58 ± 0·43; benthics, 3·63 ± 0·27). In addition, limnetics had significantly lower drag coefficients (C_D) than benthics (limnetics, log₁₀C_D = ?0·49log₁₀R_e + 0·66; benthics, log₁₀C_D = ?0·26log₁₀R_e ? 0·30) where R_e is the Reynolds number [(L_SU (ν^?1), where U and ν are swimming velocity and the kinematic viscosity of the water, respectively]. Compared to their ancestral form, the anadromous three‐spined stickleback Gasterosteus aculeatus L., limnetics and benthics had significantly longer and shorter endurance times, respectively. In addition, both these fishes had significantly higher fast‐start velocities than their ancestral form. Selection due to differential resource use may have lead to divergence of body form, and, therefore, of steady swimming performance. Therefore predation may be the selective force for the similar high escape performance in these two fishes.