Slower Relative Growth Rates Research Articles

Effects of Intraspecific Competition and Larval Size on Bioconversion of Apple Pomace Inoculated with Black Soldier Fly

Waste from apple juice and cider industries (pomace) compares poorly against spent grains and other relatively high-nutrient wastes as a substrate for bioconversion by the black soldier fly (BSF: Hermetia illucens). However, global pomace production exceeds 24 million tonnes annually and novel management approaches are required to reduce waste to landfill. We examined the effects of BSF inoculation densities (intraspecific competition) and larval size categories on cohort weight gains and apple pomace waste reduction. We found that, by increasing larval densities, cohort biomass and bioconversion rates (BRs) increased; however, at very high densities (overcrowding), BRs declined and cohorts lost weight. Furthermore, larger larval size classes accelerated substrate desiccation, possibly because of greater demands for water by older larvae. Larger larvae have slower relative growth rates and BRs compared to smaller size categories and require comparatively less dry weight substrate. Our results suggest that overcrowding on low-nutrient substrates reduces BRs and could exaggerate differences between BSF relative performances in comparative studies, particularly if intraspecific interference competition for space and exploitation competition for water diminish BSF weight returns at the end of the bioconversion cycle. We make a series of recommendations for the use of BSF in pomace waste reduction.

Trait-density relationships explain performance in cladoceran zooplankton.

Traits have been used extensively to predict and understand performance in response to the abiotic environment, but their role for understanding competitive interactions is less understood, especially in nonplant systems. In this study, we evaluate how traits interact with intraspecific density to modulate performance (per capita birth rate) and whether the traits associated with intraspecific competitive ability are similar across multiple species. We used an experimental system of four cladoceran zooplankton species, experimentally manipulated the density of conspecifics, and measured a range of morphological and life history characteristics (body mass, body length, second antenna length, eye diameter, relative growth rate, age at first reproduction, and birth rate). With causal modeling, we identified significant trait-density relationships for three out of four species, although the specific traits that predicted birth rate varied from species to species. In general, individuals at higher densities displayed smaller morphological traits and shifts towards slower relative growth rates and delayed onset of reproduction. We also asked more generally if there are consistent trait-mediated impacts of density across multiple species. The interspecific model identified significant trait-density relationships for body length, age at first reproduction, and relative growth rate. Unexpectedly, we found little evidence for trait-based competition due to mechanisms such as limiting similarity or hierarchical competition, and rather noted the potential for trait plasticity and constraints on plasticity affecting performance in response to the competitive environment.

Effect of acorn size on survival and growth of Quercus suber L. seedlings under water stress

While the effects of seed size on survival and early seedling growth have been demonstrated in Quercus spp., there is a knowledge gap regarding these effects under water limiting conditions. To address this need, we studied cork oak (Quercus suber L.) seedling development among treatments including three acorn classes (small: < 4 g, intermediate: 4–6 g), and large: ≥ 6 g) and two water regimes (well-watered versus water stressed). The following hypotheses were proposed: the reserve effect (larger seeds retain a larger proportion of reserves after germinating), the metabolic effect (seedlings from larger seeds have slower relative growth rates), the seedling-size effect (larger seeds produce larger seedlings), and that plant tolerance to water stress increases with increasing seed size. Acorn size had no effect on duration and rate of acorn germination nor on seedling survival, but it significantly affected almost all growth parameters, excepting the number of growth unit and leaves and leaf area. Seedlings coming from large acorns always showed the highest values for the affected growth parameters, followed by those coming from acorns of intermediate size; seedlings coming from small acorns always exhibited the lowest values. Water stress significantly affected survival rate (88.2% for well-watered seedlings versus 64.7% for water stressed seedlings) and biomass of fine roots and stems, but independently of acorn size. Our results are in line with both hypothesizes of the reserve effect and seedling-size effect, but not for the metabolic effect nor the plant tolerance to water stress increases with increasing seed size hypotheses. In general, our results show that large acorns had no advantage in survival or seedling growth under water stress comparatively to intermediate or small acorns, at least under the conditions of our experiment.

Adaptive shoot and root responses collectively enhance growth at optimum temperature and limited phosphorus supply of three herbaceous legume species.

Studies on the effects of sub- and/or supraoptimal temperatures on growth and phosphorus (P) nutrition of perennial herbaceous species at growth-limiting P availability are few, and the impacts of temperature on rhizosphere carboxylate dynamics are not known for any species. The effect of three day/night temperature regimes (low, 20/13 °C; medium, 27/20 °C; and high, 32/25 °C) on growth and P nutrition of Cullen cinereum, Kennedia nigricans and Lotus australis was determined. The highest temperature was optimal for growth of C. cinereum, while the lowest temperature was optimal for K. nigricans and L. australis. At optimum temperatures, the relative growth rate (RGR), root length, root length per leaf area, total P content, P productivity and water-use efficiency were higher for all species, and rhizosphere carboxylate content was higher for K. nigricans and L. australis. Cullen cinereum, with a slower RGR, had long (higher root length per leaf area) and thin roots to enhance P uptake by exploring a greater volume of soil at its optimum temperature, while K. nigricans and L. australis, with faster RGRs, had only long roots (higher root length per leaf area) as a morphological adaptation, but had a higher content of carboxylates in their rhizospheres at the optimum temperature. Irrespective of the species, the amount of P taken up by a plant was mainly determined by root length, rather than by P uptake rate per unit root surface area. Phosphorus productivity was correlated with RGR and plant biomass. All three species exhibited adaptive shoot and root traits to enhance growth at their optimum temperatures at growth-limiting P supply. The species with a slower RGR (i.e. C. cinereum) showed only morphological root adaptations, while K. nigricans and L. australis, with faster RGRs, had both morphological and physiological (i.e. root carboxylate dynamics) root adaptations.

Competitive abilities among seedlings of three tree species differing in seed size: A garden experiment using species of Chilean temperate forest

evidence suggests that seedlings of large‐seeded species have an initial size advantage but also tend to have slower relative growth rates (RGR). In a 1‐yr garden experiment in southern Chile, we address whether early size advantages or disadvantages shown by 3‐month‐old seedlings of three tree species differing markedly in seed size (Persea lingue > Peumus boldus > Drimys winteri) confer them with greater or lesser competitive abilities when grown in species mixtures in the following 12 months of development. Given the reported negative relationship between seed size and RGR, we predicted a negative relationship between seed size and competitive ability among these three species (i.e., D. winteri > P. boldus > P. lingue). Seedlings of D. winteri, the species producing the smallest seeds, had clear and strong negative effects on the growth of seedlings of both P. boldus and P. lingue. likewise, P. boldus, the species producing medium‐sized seeds, had strong negative effects on the growth of seedlings of the other two species. in addition, negative effects of D. winteri on P. boldus were generally greater than vice versa. Seedlings of P. lingue did not affect the growth of the other two species. Therefore, our results support the predicted hierarchy of competitive abilities, i.e., D. winteri > P. boldus > P. lingue.

Seed‐mass effects in four Mediterranean Quercus species (Fagaceae) growing in contrasting light environments

Three hypotheses have been proposed to explain the functional relationship between seed mass and seedling performance: the reserve effect (larger seeds retain a larger proportion of reserves after germinating), the metabolic effect (seedlings from larger seeds have slower relative growth rates), and the seedling-size effect (larger seeds produce larger seedlings). We tested these hypotheses by growing four Mediterranean Quercus species under different light conditions (3, 27, and 100% of available radiation). We found evidence for two of the three hypotheses, but none of the four species complied with all three hypotheses at the same time. The reserve effect was not found in any species, the metabolic effect was found in three species (Q. ilex, Q. pyrenaica, and Q. suber), and the seedling-size effect in all species. Light availability significantly affected the relationships between seed size and seedling traits. For Q. ilex and Q. canariensis, a seedling-size effect was found under all three light conditions, but only under the lowest light (3%) for Q. suber and Q. pyrenaica. In all species, the correlation between seed mass and seedling mass increased with a decrease in light, suggesting that seedlings growing in low light depend more upon their seed reserves. A causal model integrates the three hypotheses, suggesting that larger seeds generally produced larger seedlings.

Relative growth rate, resource allocation and root morphology in the perennial legumes, Medicago sativa, Dorycnium rectum and D. hirsutum grown under controlled conditions

Perennial pastures are needed in farming systems in southern Australia to combat environmental problems such as dryland salinity. The mediterranean climate in southern Australia imposes constraints to the growth and survival of perennial plants. The aim of this study was to compare growth rates, resource allocation and root distribution in three perennial legumes, Medicago sativa L., Dorycnium hirsutum (L.) Ser. and Dorycnium rectum (L.) Ser., to identify different plant traits and their ecological and agronomic significance. Plants were grown in 1-m deep split tubes and destructive harvests were made every 2 weeks after plant emergence for 10 weeks. Leaf area and leaf, stem and root fresh and dry weights were measured. Maximum root depth and the root distribution were also determined. Seedlings of Dorycnium were slower to emerge and had a lower relative growth rate (RGR) than M. sativa. The slower RGR was associated with a lower specific leaf area (SLA) in D. hirsutum and a lower net assimilation rate (NAR) in D. rectum. Although all species allocated a similar proportion of biomass to roots, D. rectum had a shallower root distribution and took longer to produce deep roots. The slow growth rates of Dorycnium seedlings suggest that they are more prone to establishment problems due to competition from weeds or other pastures, and because they have less access to water at greater depth during summer drought. However, D. hirsutum displayed characteristics of a plant that is adapted to stressful environments and therefore may be able to grow in conditions where other perennial legumes cannot.

Molecular and morphological character inheritance in hybrids of Alaria esculenta and A. praelonga (Alariaceae, Phaeophyceae)

Hybridization of Alaria esculenta and A. praelonga (Phaeophyceae. Laminariales, Alariaceae) resulted in successful and healthy progeny. Morphological characters, relative growth rates and Rubisco spacer sequences of hybrids were compared with the parental plants. The results show that hybrids inherit the morphological characters from the A. praelonga gametophytes, indicating that these characters are not sex-linked and are dominant. The relative growth rates were significantly different among the F1, with the A. esculenta self-cross progeny showing the fastest relative growth rate for length compared to the other cross combinations. The A. praelonga self-cross progeny also grew significantly faster than the progeny from hybrid crosses, which did not differ significantly from each other. The A. esculenta and A. praelonga self-cross F1 did not differ significantly in relative growth rate for width. Hybrid progeny showed a significant slower relative growth rate for width, compared to the A. esculenta self-cross progeny but did not differ significantly from each other. A comparison of Rubisco spacer sequence alignments showed that the Rubisco spacer is inherited via the female gametophyte in Alaria, which is in accordance with results found in other members of the Laminariales. Chloroplast DNA is probably inherited maternally in all Laminariales. Analysis of the Rubisco sequences revealed one mutation in the large subunit in the female A. esculenta × male A. praelonga hybrid. Effects of this mutation on the amino acid coded are discussed.

Effects of Diet-Age and Streptomycin on Virulence ofAutographa californicaM Nucleopolyhedrovirus against the Tobacco Budworm

Addition of the antibiotic streptomycin to two artificial diets routinely used in bioassays of neonate lar vae ofHeliothis virescens(tobacco budworm) infected withAutographa californicaM nucleopolyhedrovirus (AcMNPV) increased lethal times of the virus. After storage of diets for 3 weeks at 4°C, lethal times of infected larvae were significantly slower compared to those for larvae bioassayed using diets stored for 2 weeks or less. The effect of diet-age on rate of mortality was not the result of a change in total protein content or pH of the diet, but was apparently the result of some other alteration in the quality of the diet (e.g. microbial spoilage, palatibility, and/or nutritional value unrelated to total protein). Although we did not determine why lethal times were slower in response to streptomycin concentration or diet-age, we did find that slower lethal times were correlated with slower relative growth rates (RGR) of infected larvae. In addition, RGR of infected larvae decreased as a function of increasing streptomycin concentration, diet-age, and the interaction of the two factors. These results demonstrate that it is difficult to obtain consistent and comparable bioassay results if antibiotic composition and diet-age are not controlled. We suggest a standardized diet or highly standardized procedures for a given diet be developed that permits comparison of bioassays among and within laboratories.

Growth patterns of Chianina bull from 6 to 24 months fed two different diets. 1. Organs and carcass

Abstract Sixty-nine Chianina young bulls were fed two unifeed diets to ad libitum intake (an H diet, 0.94 UFV/kg DM, and an L diet, 0.76 UFV/kg DM) beginning from six months of age, and were serially slaughtered at two-month intervals from 8 to 24 months of age. A further eight calves were slaughtered at six months as an initial reference. At slaughter, the weight of the organs, body parts and anatomical cuts was recorded. Statistical analysis used the allometric equation, and variations in the growth coefficient were tested by the log-log relationship of the second or third degree. On average, the testicle, visceral fat, carcass and hide grew faster than the whole body, while the other body components exhibited growth coefficients that were less than unity. Generally thoracic organs presented a higher coefficient than abdominal organs. Carcass and heart exhibited self-accelerating growth. The hide, the head, some digestive organs and the testicle had an intense growth rate during the initial phase but decreased their growth impetus later as BW increased. Diet influenced the instantaneous relative growth rate of the stomachs, hide, tongue and testicle which appeared sensitive to functional demand, or to evolution over time, and which showed a higher proportion in L than H diet bulls at an average EBW. A caudo-cranial and disto-proximal gradient of growth was detected in anatomical cuts and no variation in the allometric coefficient was found in the carcass regions. The H diet determined a slower relative growth rate of the hindlimb but a faster growth rate of cavity fat and of the abdominal wall.

Morphological and growth rate differences among outcrossing and self‐pollinating races of Arenaria uniflora (Caryophyllaceae)

AbstractPopulations of Arenaria uniflora exhibit intraspecific variation in floral size and degree of protandry in association with the evolution of self‐pollination. Heterochrony, or a simple change in the absolute timing or rate of developmental events, is proposed as the evolutionary mechanism underlying the origin of the small, self‐pollinating flowers from their large, outcrossing progenitors. Inflorescence growth in two autogamous populations and their related outcrossing progenitors was studied to provide the temporal data necessary for testing the hypothesis of heterochrony. All four races showed significant variation in the growth and mature length of inflorescence organs. Inflorescences of selfing races were smaller, and had slower relative growth rates and a two‐fold increase in the plastochron relative to outcrossing populations. The large‐flowered races were both significantly protandrous. A more detailed growth analysis of flower development in two races indicated that the selfing flowers develop at a slower rate and for a longer duration relative to outcrossing flowers. The implications of these temporal changes in floral ontogeny for the heterochronic origin of self‐pollinating floral forms are considered.

Fish Community Structure and Function along Two Habitat Gradients in a Headwater Stream

The stream continuum concept suggests that the physical structure of the stream channel coupled with the hydrological cycle and energy inputs results in a consistent pattern of community structure and function along a stream. I evaluated this concept in a headwater fish community along two physical gradient gradients: upstream to downstream and riffle to pool. Habitat diversity and volume increased from upstream to downstream, and from riffle to pool. Temporal variation in habitat diversity was greater upstream. Upstream, and in riffles, habitat volume tended to vary more with time. Fluctuations in rainfall regime caused annual variation in habitat, especially in volume. Benthic insect density was highest from autumn (October—November) through spring (May—June). Following emergence of adults in late spring, invertebrate densities were low in summer in areas with riparian vegetation, but were not lower where riparian vegetation was absent and stable substrates were present. Along a gradient of substrates from silt—sand to gravel—rock, insect production increased, as indicated by adults and pupae in the drift. Peak resource availability for insectivore—piscivore fishes occurred in late summer and autumn, due to increased abundance of young—of—the—year fish. Pool and raceway—pool habitat guilds and insectivore and insectivore—piscivore trophic guilds contained the largest number of species. Increases in species richness were primarily associated with the addition of deeper habitats. Species richness of the pool insectivore—piscivore guild was especially variable over time. Biomass in shallow areas consisted predominantly of generalized insectivores. In deep, stable habitats, generalized insectivores were replaced as the predominant trophic group by insectivore—piscivores and large benthic insectivores. Immigration of fish occurred in spring and autumn, the periods of highest resource availability. Immigration between midriver and headwater regions primarily involved older age classes (III+), and was associated with changes in flow regime, habitat structure, and seasonal dynamics of the resource base of particular trophic groups. Flow regime and habitat volume appeared to be important factors limiting immigration in autumn, especially in pool species. Habitat diversity (depth, current, and substrate; DCS) was significantly correlated with fish species diversity (FSD). However, considerable variation occurred in the relationship between the two variables, including: (1) FSD decreased in winter in shallow, less diverse habitats due to emigration, and increased in spring due to recolonization; (2) FSD increased in spring and autumn when resource availability increased; (3) FSD was least predictable from DCS in autumn, when flow regimes were low and large numbers of fish recruits were present; and (4) DCS did not predict FSD as accurately in temporally variable upstream areas where large numbers of small fish dominated the community, especially in areas with human disturbance. Young age groups (0—II) were primarily found in shallow, temporally variable areas upstream and in riffles. Relative growth rates were highest during summer months. However, growth rates did not increase as much between spring and summer as would have been predicted from the seasonal increase in water temperature, suggesting that resource limitation may have occurred during summer periods. Centrarchids had substantially higher growth rates than cyprinids during early life stages. Net production for age 0—II fish was highest in upstream and riffle areas because of high densities of young, generalized insectivores. Net production of insectivore—piscivores was highest in downstream and pool habitats. Development of large, stable pools and raceways resulted in decreased fish production due to shifts in age structure toward fewer, large individuals with slower relative growth rates (age III+). Temporal variation in reproductive success and survival of younger age groups (0—I) was associated with random variation in high flow regimes and appeared to be a major factor determining spatial and temporal variation in production. These patterns of fish community structure and function support the qualitative aspect of the stream continuum concept: consistent shifts in community organization are associated with spatial or temporal changes in channel morphology and resource availability. However, for the stream continuum concept to be useful as a quantitative predictor, the ultimate mechanism(s) regulating fish community organization need to be more rigorously established. I hypothesize that in upstream or riffle areas, where younger age classes predominate, recolonization dynamics, the effect of gradual changes in physical conditions on competitive interactions, and temporal variation in reproductive success, are more important than competitive exclusion and predation as determinants of community organization.