Does food supplementation really enhance productivity of breeding birds?

Food availability influences multiple stages of the breeding cycle of birds, and supplementary feeding has helped in its understanding. Most supplementation studies have reported advancements of laying, whilst others, albeit less numerous, have also demonstrated fitness benefits such as larger clutches, shorter incubation periods, and greater hatching success. Relatively few studies, however, have investigated the effects of supplementary feeding for protracted periods across multiple stages of the breeding cycle. These effects are important to understand since long-term food supplementation of birds is recommended in urban habitats and is used as a tool to increase reproductive output in endangered species. Here, we compare the breeding phenology and productivity of blue tits Cyanistes caeruleus and great tits Parus major breeding in food-supplemented and non-supplemented blocks in a broadleaf woodland in central England over three seasons (2006–2008). Supplementation was provided continuously from several weeks pre-laying until hatching, and had multiple significant effects. Most notably, supplementation reduced brood size significantly in both species, by half a chick or more at hatching (after controlling for year and hatching date). Reduced brood sizes in supplemented pairs were driven by significantly smaller clutches in both species and, in blue tits, significantly lower hatching success. These are novel and concerning findings of food supplementation. As expected, supplementary feeding advanced laying and shortened incubation periods significantly in both species. We discuss the striking parallels between our findings and patterns in blue and great tit reproduction in urban habitats, and conclude that supplementary feeding may not always enhance the breeding productivity of birds.     

Does interference competition with wolves limit the distribution and abundance of coyotes?

Interference competition with wolves Canis lupus is hypothesized to limit the distribution and abundance of coyotes Canis latrans, and the extirpation of wolves is often invoked to explain the expansion in coyote range throughout much of North America. We used spatial, seasonal and temporal heterogeneity in wolf distribution and abundance to test the hypothesis that interference competition with wolves limits the distribution and abundance of coyotes. From August 2001 to August 2004, we gathered data on cause-specific mortality and survival rates of coyotes captured at wolf-free and wolf-abundant sites in Grand Teton National Park (GTNP), Wyoming, USA, to determine whether mortality due to wolves is sufficient to reduce coyote densities. We examined whether spatial segregation limits the local distribution of coyotes by evaluating home-range overlap between resident coyotes and wolves, and by contrasting dispersal rates of transient coyotes captured in wolf-free and wolf-abundant areas. Finally, we analysed data on population densities of both species at three study areas across the Greater Yellowstone Ecosystem (GYE) to determine whether an inverse relationship exists between coyote and wolf densities. Although coyotes were the numerically dominant predator, across the GYE, densities varied spatially and temporally in accordance with wolf abundance. Mean coyote densities were 33% lower at wolf-abundant sites in GTNP, and densities declined 39% in Yellowstone National Park following wolf reintroduction. A strong negative relationship between coyote and wolf densities (beta = -3.988, P < 0.005, r(2) = 0.54, n = 16), both within and across study sites, supports the hypothesis that competition with wolves limits coyote populations. Overall mortality of coyotes resulting from wolf predation was low, but wolves were responsible for 56% of transient coyote deaths (n = 5). In addition, dispersal rates of transient coyotes captured at wolf-abundant sites were 117% higher than for transients captured in wolf-free areas. Our results support the hypothesis that coyote abundance is limited by competition with wolves, and suggest that differential effects on survival and dispersal rates of transient coyotes are important mechanisms by which wolves reduce coyote densities.     

Does nitrogen availability control rates of litter decomposition in forests?

The effects of increased exogenous N availability on rates of litter decomposition were assessed in several field fertilization trials. In a jack pine (Pinus banksiana Lamb.) forest, needle litter decomposed at the same rate in control plots and in plots fertilized with urea and ammonium nitrate (1350 kg N ha^-1) with or without P and K. Mixed needle litter of western hemlock (Tsuga heterophylla (Raf.) Sarg.), western red cedar (Thuja plicata Donn) and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) incubated in plots recently amended with sewage sludge (500 kg N ha^-1) lost less weight during 3 years than did litter in control plots. Forest floor material also decomposed more slowly in plots amended with sewage sludge. Paper birch (Betula papyrifera Marsh.) leaf litter placed on sewage sludge (1000 kg N ha^-1), pulp sludge, or sewage-pulp sludge mixtures decomposed at the same rate as leaf litter in control plots. These experiments demonstrate little effect of exogenous N availability on rates of litter decomposition.The influence of endogenous N availability on rates of litter decomposition was examined in a microcosm experiment. Lodgepole pine (Pinus contorta var. latifolia Engelm.) needle litter collected from N-fertilized trees (525 kg N ha^-1 in ammonium nitrate) were 5 times richer in N than needles from control trees (1.56% N versus 0.33% N in control trees), but decomposed at the same rate. Green needles from fertilized trees contained twice as much N as needles from control trees (1.91% N versus 0.88% N), but decomposed at the same rate. These experiments suggest that N availability alone, either exogenous or endogenous, does not control rates of litter decomposition. Increased N availability, through fertilization or deposition, in the absence of changes in vegetation composition, will not alter rates of litter decomposition in forests.     

Patterns in benthic food webs: a role for omnivorous crayfish?

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty-one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond. 2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance. 3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment-dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)). 4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte-associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish. 5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density. 6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.     

Does fitness erode in the absence of selection? An experimental test with Tribolium

In the absence of natural selection, average fitness in the population is expected to decline due to the accumulation of deleterious mutations. Replicate populations of flour beetles (Tribolium confusum) were maintained for 22 generations in the virtual absence of selection (random mating, favorable environment, excess of food, and mortality of only 3%). Larva-to-adult survivorship rates were similar in the stock population and selection-free populations. In contrast, starvation resistance of adult beetles from selection-free populations was significantly reduced (by more than 2% per generation). When tested in the favorable environment, beetles in one selection-free population had significantly slower development and smaller sizes of females than beetles from the stock population. Since such changes in these fitness components are usually maladaptive, they indicate possible erosion of fitness under relaxed selection at the rate of 0.1-0.2% per generation. No fitness erosion was detectable in the second selection-free population.     

Choice of scan-sampling intervals—An example with quantifying neighbours in dairy cows

To date, only a few studies using scan-sampling intervals to record neighbours in groups of animals explain how the interval length was chosen. In this study, we investigated the effects of different scan-sampling intervals, behavioural context, and the definition of neighbours on the accuracy of data as compared to a quasi-continuous observation. The data was collected from dairy cows kept in cubicle housing systems. Dairy herds of 22–43 cows on 6 farms were observed once a minute with an automatic tracking system for 6 days, and both the nearest neighbour and all neighbours within a defined distance of each cow were recorded with references to the activity, feeding and lying area and stored in neighbourship matrices. In the analysis, we used data collected at intervals of 2, 3, 4, …, 30 min, and correlated this simulated data with the data based on the 1-min interval using a specialised correlation coefficient for matrices τ_Kr. This correlation coefficient was then used as the response variable in mixed-effects models. We found that the size of the correlation coefficients generally decreased as interval length increased. This decrease was less pronounced for all neighbours than for the nearest neighbour. Moreover, the decrease was greatest with data from the activity area and lowest with data from the lying area. We concluded that, even with the relatively slow dairy cows in a barn environment, neighbour recordings should be conducted at short scan-sampling intervals in order to achieve a minimum correlation of τ_Kr = 0.8 with the quasi-continuous data. Intervals of every 2, 8 and 17 min are recommended for observation of neighbours in dairy cows for the activity, feeding and lying areas, respectively, and species that move faster may well require even shorter sampling intervals.     

Does persistence of showy calyces in Limonium leptolobum enhance pollinator attraction?

Aims The calyx, the outermost whorl of a flower (usually green), has been considered to function to protect flowers. In some species, however, calyces are colorful and retained during seed development. Limonium species have been exploited as cut flower crops because the calyces persist for several months after the corolla has closed. To explore the adaptive significance of the persistent calyx in a desert plant Limonium leptolobum, we ask whether persistence of calyces can enhance pollinator attraction by enlarging floral displays, increasing reproductive success in this self-incompatible species.Methods The yellow flower of L. leptolobum lasted 1–2 days but its white, membranous calyx extended fully after the corolla closed, and persisted for over 2 months in the field, making hundreds of 'showy flowers' on one individual. To examine the ecological function of calyces, we test the pollinator attraction hypothesis. In an experimental population, we compared the difference in visit frequency and visitor behavior between intact inflorescences and inflorescences with their calyces removed on the same individual plants.Important findings In four experimental plots four types of floral visitors were observed including bees, butterflies, syrphid flies and day-flying moths. No significant preference was observed between calyx-free and intact inflorescences for both first arrivals and total visit frequency of all types of floral visitors, indicating that the persistence of calyces did not make plants more attractive to potential pollinators. The pollinator attraction hypothesis for the showy calyces was not supported by the current data. Whether the calyx in this desert plant helps seed development or has other functions needs further study.     

Can habitat characteristics shape vertebral morphology in dolphins? An example of two phylogenetically related species from southern South America

Fast swimming pelagic cetacean species have osteological characteristics that promote a more stable spine in comparison to that of coastal species. The Peale's dolphin (Lagenorhynchus australis) and the hourglass dolphin (Lagenorhynchus cruciger) have a close phylogenetic relationship and are found in coastal and pelagic waters in the Southern Hemisphere, respectively. The aim of this work was to study the relationship between the vertebral column's morphology and its flexibility, across these species of contrasting habitats. Vertebral counts and multiple measurements of each vertebra were used to infer intervertebral flexibility. Bivariate plots and discriminant multivariate analyses were employed to compare each functional region along the vertebral column. Both species displayed a regionalization of the column into three stable regions and two flexible areas, which statistically differ in the proportion of the skeleton occupied in each species. While the Peale's dolphin has rounder vertebrae, associated with higher flexibility, the hourglass dolphin has disk‐shaped vertebrae and strongly inclined processes related to high stability. Although the species are closely related phylogenetically, vertebral morphology is influenced by a diverse set of ecological and behavioral factors, reflecting a high degree of vertebral plasticity within the genus.     

An analysis of codon usage in mammals: Selection or mutation bias?

Summary A new statistical test has been developed to detect selection on silent sites. This test compares the codon usage within a gene and thus does not require knowledge of which genes are under the greatest selection, that there exist common trends in codon usage across genes, or that genes have the same mutation pattern. It also controls for mutational biases that might be introduced by the adjacent bases. The test was applied to 62 mammalian sequences, the significant codon usage biases were detected in all three species examined (humans, rats, and mice). However, these biases appear not to be the consequence of selection, but of the first base pair in the codon influencing the mutation pattern at the third position.     

Does limb length predict the relative energetic cost of locomotion in mammals?

Do relatively longer limbs result in a lower energetic cost of locomotion? To determine whether or not cost is correlated with limb length in some way other than that due to their respective relationships to body mass, we have removed the effects of size by calculating the residuals of the relationship between each character and body size. We then regressed the pairs of residuals on one another. Because biological variables do not occur in a series of units that have evolved independently, the degree of divergence of two species is likely to be influenced by the length of time since they last shared a common ancestor. We therefore corrected for the phylogenetic relatedness of species. Data on the energetic cost of locomotion of a wide variety of species were taken from published sources. Data on limb lengths were taken from specimens in various museum collections which were similar in body mass (± 12%) to the specimens on which the cost measurements were made. None of the correlations between the residuals of either fore- or hindlimb length and neither of two estimates of the cost of locomotion was significant at P = 0.05. It is concluded that limb length does not importantly influence an animal's locomotor efficiency. These results do not imply the lack of a close relationship between cost and stride length.     

Revisiting Beverton–Holt recruitment in the presence of variation in food availability

Understanding density-dependent changes in juvenile survival and growth rates is of great importance because these rates determine recovery rates for imperiled populations and/or sustainable harvest rates. Unfortunately, the mechanisms leading to density dependent survival and growth are among the least understood process in biology and fisheries. Previous work has shown that small fish may vary foraging times to achieve a target growth rate, resulting in the well-known Beverton–Holt recruitment function with variation in food availability affected the initial slope of the recruitment curve. We amend their derivation to show that incorporating fish growth under a variety of evolutionary strategies for balancing foraging time and predation risk still leads to recruitment approximately as expected under the Beverton–Holt recruitment model but that changing food availability affects both the initial slope and maximum recruitment level. We demonstrate that when food availability is known to vary over time, these models often result in a more parsimonious alternative than the standard Beverton–Holt function. Further, Beverton–Holt recruitment is expected when foraging times are adjusted to balance fitness gains from growth against mortality risk. Finally, linking recruitment success to food availability warns that species with high scope for density dependent survival (high compensation ratio or steepness) may be extremely sensitive to changes in available food densities. This work emphasizes the sensitivity of stock-recruitment parameters to food availability and strongly suggests a need to carefully monitor lower trophic levels to better understand and predict dramatic changes in juvenile recruitment and carrying capacity.     

Can silicon in glacial rock flour enhance phosphorus availability in acidic tropical soil?

Plant and Soil - Plant-available silicon (Si) is limited in strongly weathered tropical soils. The aim of the study was to evaluate Si fertilisation as a strategy to improve phosphorus (P)...     

Paranthropus boisei: An example of evolutionary stasis?

Of the presently recognised early hominid species, Paranthropus boisei is one of the better known from the fossil record and arguably the most distinctive; the latter interpretation rests on the numbers of apparently derived characters it incorporates. The species as traditionally diagnosed is distributed across approximately one million years and is presently confined to samples from East African sites. The hypodigm has been examined for evidence of intraspecific phyletic evolution, with particular emphasis on the areas best represented in the fossil record, namely the teeth and mandible. The results of this examination of 55 mandibular and dental variables, which uses the Γ test statistic for the detection of trend, and nonparametric spline regression (Loess regression) for investigating pattern and rate of temporal change, show that within Paranthropus boisei sensu stricto most evidence of temporally related morphological trends relates to the morphology of the P₄ crown. There is little or no evidence of any tendency to increase in overall size through time. Fossils from the Omo Shungura Formation and West Turkana which have been recovered from a time period earlier than the P. boisei sensu stricto hypodigm resemble the latter taxon in some features, but differ from it in aspects of cranial morphology. There is insufficient fossil evidence of the earlier taxon to tell whether it changes through time, but when trends of 47 mandibular and dental variables are assessed across the combined East African “robust” australopithecine sample, there is evidence for a relatively abrupt change around 2.2–2.3 Myr in approximately 25% of the dental and mandibular remains. Some of these changes correspond with the temporal trends within P. boisei sensu stricto, but others, such as mandible height, do not. If the earlier material is ancestral to P. boisei sensu stricto, evidence from the teeth and jaws is consistent with a punctuated origin for the latter taxon. © 1994 Wiley-Liss, Inc.     

Does the proportion of arthropods versus fruit in the diet influence overwintering condition of an omnivorous songbird?

Many migratory songbirds switch from a primarily insectivorous diet during the breeding season to either a mixed diet or fruit diet during the non‐breeding season. However, for species with mixed diets, arthropods may be superior food items because of their higher protein content and easier digestibility. We tested this hypothesis by analyzing the diet and body condition of omnivorous Wood Thrushes (Hylocichla mustelina) at a non‐breeding site in tropical forest in Belize, Central America. We used analysis of stable isotopes δ¹⁵N and δ¹³C in the blood to measure diet. Our objective was to determine if a higher dietary proportion of arthropods relative to fruit (i.e., higher δ¹⁵N and δ¹³C) was associated with better body condition. We also examined the possible effect of age, sex, and habitat type on Wood Thrush diets, as well as any changes in diet through the overwintering period. We used a hierarchical Bayesian mixing model (MixSIAR) to estimate the proportion of different prey items in the diet of overwintering Wood Thrushes overall, in each habitat type, and over time during the non‐breeding period. From January to April, we found a significant decline in δ¹⁵N in forest habitats, whereas δ¹⁵N increased in scrub habitat. There was no significant seasonal change in δ¹³C. Birds with higher δ¹⁵N or δ¹³C values were not in better body condition. Females in dry‐scrub habitat consumed more fruit than males, but this did not affect body condition. Mixing model results indicated that most Wood Thrushes at our study sites consumed primarily arthropods, even during the driest times of the non‐breeding season and in the driest habitat. Overall, our results suggest that the diet of Wood Thrushes varies with habitat and during the overwintering period, but diet alone was not a predictor of body condition. Wood Thrushes, and possibly other omnivorous migratory songbirds, are apparently flexibly able to meet their wintering and pre‐migration nutritional demands with a variety of diets.     

Does diet in Celtic Sea fishes reflect prey availability?

Feeding preferences of Celtic Sea fishes were investigated using a database of stomach content records, collected between 1977 and 1994. The diet of cod Gadus morhua , hake Merluccius merluccius , megrim Lepidorhombus whiffiagonis , whiting Merlangius merlangus and saithe Pollachius virens changed markedly as the animals grew larger, and although large predators generally chose larger bodied prey, the variability of prey sizes consumed also increased. Large predators continued to select small, low value, benthic prey ( e.g . Callionymus spp. and Trisopterus spp.) which were easier to catch, rather than larger, more energy lucrative pelagic prey ( e.g . mackerel Scomber scombrus ), even though these pelagic prey‐fishes were nearly always available and were often very abundant. Stock estimates of the International Council for the Exploration of the Sea and U.K. groundfish survey catches were used as indices of prey abundance. Blue‐whiting Micromesistius poutassou and other small pelagic fishes ( Argentina spp. and clupeoids) were identified as being particularly important, and were consumed by some predators more often than would be expected given the abundance of these prey in the environment. There was no evidence for density‐dependent feeding by predators on mackerel and only hake exhibited density‐dependent feeding on horse‐mackerel. Hake, cod and megrim consumed more blue‐whiting when this prey was at higher abundance in the environment. In choosing what prey to consume, predators must balance costs and benefits, considering the quality of prey and the energy expended during search, capture and handling.     

Does colour polymorphism enhance survival of prey populations?

That colour polymorphism may protect prey populations from predation is an old but rarely tested hypothesis. We examine whether colour polymorphic populations of prey exposed to avian predators in an ecologically valid visual context were exposed to increased extinction risk compared with monomorphic populations. We made 2976 artificial pastry prey, resembling Lepidoptera larvae, in four different colours and presented them in 124 monomorphic and 124 tetramorphic populations on tree trunks and branches such that they would be exposed to predation by free-living birds, and monitored their ‘survival’. Among monomorphic populations, there was a significant effect of prey coloration on survival, confirming that coloration influenced susceptibility to visually oriented predators. Survival of polymorphic populations was inferior to that of monomorphic green populations, but did not differ significantly from monomorphic brown, yellow or red populations. Differences in survival within polymorphic populations paralleled those seen among monomorphic populations; the red morph most frequently went extinct first and the green morph most frequently survived the longest. Our findings do not support the traditional protective polymorphism hypothesis and are in conflict with those of earlier studies. As a possible explanation to our findings, we offer a competing ‘giveaway cue’ hypothesis: that polymorphic populations may include one morph that attracts the attention of predators and that polymorphic populations therefore may suffer increased predation compared with some monomorphic populations.     

Does increased endogenous CCK interact with serotonin to reduce food intake in rats?

The present study was aimed to test the hypothesis that increased endogenous CCK may interact with the anorectic serotonergic agent dl-fenfluramine to reduce food intake in rats. Previous studies, using selective CCK receptor antagonists, could demonstrate CCK-dependent 5-HT-induced anorexia. In the present approach, we used protease inhibitors to increase levels of endogenous CCK instead of blocking CCK receptors by antagonists. The protease inhibitors we used were soybean trypsin inhibitor (STI) and camostate. We hypothesized that combining the anorectic serotonergic drug dl-fenfluramine with either STI or camostate should result in an enhanced hypophagic effect when compared to single drug treatment. All feeding experiments were performed in non-deprived rats during night time feeding. Given alone, STI (500 mg/kg, po), camostate (200 mg/kg po) and also fenfluramine (1–9 mg/kg ip) reduced significantly food intake, with a more pronounced effect following fenfluramine. However, the experiments do not provide evidence for any additive or synergistic action between camostate or STI and the anorectic serotonergic drug dl-fenfluramine on food intake.     

Does energy availability influence classical patterns of spatial variation in exotic species richness?

Aim At macroecological scales, exotic species richness is frequently positively correlated with human population density. Such patterns are typically thought to arise because high human densities are associated with increased introduction effort and/or habitat modification and disturbance. Exotic and native species richness are also frequently positively correlated, although the causal mechanisms remain unclear. Energy availability frequently explains much of the variation in species richness and we test whether such species–energy relationships may influence the relationships of exotic species richness with human population density and native species richness. Location Great Britain. Methods We first investigate how spatial variation in the distributions of the 10 exotic bird species is related to energy availability. We then model exotic species richness using native avian species richness, human population density and energy availability as predictors. Species richness is modelled using two sets of models: one assumes independent errors and the other takes spatial correlation into account. Results The probability of each exotic species occurring, in a 10‐km quadrat, increases with energy availability. Exotic species richness is positively correlated with energy availability, human population density and native species richness in univariate tests. When taking energy availability into account, exotic species richness is negligibly influenced by human population density, but remains positively associated with native species richness. Main conclusions We provide one of the few demonstrations that energy availability exerts a strong positive influence on exotic species richness. Within our data, the positive relationship between exotic species richness and human population density probably arises because both variables increase with energy availability, and may be independent of the influence of human density on the probability of establishment. Positive correlations between exotic and native species richness remain when controlling for the influence of energy on species richness. The relevance of such a finding to the debate on the relationship between diversity and invasibility is discussed.     

Flowering phenology: An example of relaxation of natural selection?

Flowering phenology has normally been viewed as fundamental to a plant species' reproductive ecology. Researchers in the field have emphasized the adaptive importance of flowering at a particular time relative to other individuals in the population, or other species in the community. An alternative view, however, is that flowering phenology is a trait that may not be under strong selection, and this may have allowed some variation to appear in populations by chance.     

Is abundance a species attribute? An example with haematophagous ectoparasites

Population density is a fundamental property of a species and yet it varies among populations of the same species. The variation comes from the interplay between intrinsic features of a species that tend to produce repeatable density values across all populations of the same species and extrinsic environmental factors that differ among localities and thus tend to produce spatial variation in density. Is inter-population variation in density too large for density to be considered a true species character? We addressed this question using data on abundance (number of parasites per individual host, i.e. equivalent to density) of fleas ectoparasitic on small mammals. The data included samples of 548 flea populations, representing 145 flea species and obtained from 48 different geographical regions. Abundances of the same flea species on the same host species, but in different regions, were more similar to each other than expected by chance, and varied significantly among flea species, with 46% of the variation among samples accounted by differences between flea species. Thus, estimates of abundance are repeatable within the same flea species. The same repeatability was also observed, but to a lesser extent, across flea genera, tribes and subfamilies. Independently of the identity of the flea species, abundance values recorded on the same host species, or in the same geographical region, also showed significant statistical repeatability, though not nearly as strong as that associated with abundance values from the same flea species. There were also no strong indications that regional differences in abiotic variables were an important determinant of variation in abundance of a given flea species on a given host species. Abundance thus appears to be a true species trait in fleas, although it varies somewhat within bounds set by species-specific life history traits.