Temperature,resources and predation interact to shape phytoplankton size–abundance relationships at a continental scale

Aim

Communities contain more individuals of small species and fewer individuals of large species. According to the ‘metabolic theory of ecology’, the relationship of log mean abundance with log mean body size across communities should exhibit a slope of −3/4 that is invariant across environmental conditions. Here, we investigate whether this slope is indeed invariant or changes systematically across gradients in temperature, resource availability and predation pressure.

Location

1048 lakes across the USA.

Time Period

2012.

Major Taxa Studied

Phytoplankton.

Results

We found that the size–abundance relationship across all sampled phytoplankton communities was significantly lower than −3/4 and near −1 overall. More importantly, we found strong evidence that the environment affects the slope: it varies between −0.33 and −0.93 across interacting gradients of temperature, resource (phosphorus) supply and zooplankton predation pressure. Therefore, phytoplankton communities have orders of magnitude more small or large cells depending on environmental conditions across geographical locations.

Conclusion

Our results emphasise the importance of the environmental factors' effect on macroecological patterns that arise through physiological and ecological processes. An investigation of the mechanisms underlying the link between individual energetics constrain and macroecological patterns would allow to predict how global warming and changes in nutrients will alter large-scale ecological patterns in the future.     

Plastic and evolutionary responses of cell size and number to larval malnutrition in Drosophila melanogaster

Both development and evolution under chronic malnutrition lead to reduced adult size in Drosophila. We studied the contribution of changes in size vs. number of epidermal cells to plastic and evolutionary reduction of wing size in response to poor larval food. We used flies from six populations selected for tolerance to larval malnutrition and from six unselected control populations, raised either under standard conditions or under larval malnutrition. In the control populations, phenotypic plasticity of wing size was mediated by both cell size and cell number. In contrast, evolutionary change in wing size, which was only observed as a correlated response expressed on standard food, was mediated entirely by reduction in cell number. Plasticity of cell number had been lost in the selected populations, and cell number did not differ between the sexes despite males having smaller wings. Results of this and other experimental evolution studies are consistent with the hypothesis that alleles which increase body size through prolonged growth affect wing size mostly via cell number, whereas alleles which increase size through higher growth rate do so via cell size.     

Effects of female body size and timing of nest foundation on the reproduction of the Japanese paper wasp,Polistes jadwigae Dalla Torre (Hymenoptera: Vespidae)

Females in hibernation site (FH) were significantly larger than foundresses (FO), suggesting that larger FH were less successful in founding their nest. Body size of FO did not correlate with two nest characters, i.e., the number of cells at pupal stage (CP) and the timing of nest foundation (DP). However, CP negatively correlated with DP in 2 of 3 studied years, suggesting that foundress who founded her nest earlier than others tended to construct larger number of cells irrespective of her body size.     

Ecology of body size in Drosophila buzzatii: untangling the effects of temperature and nutrition

Abstract.

• 1 A method of separating the effects of two important determinants of body size in natural populations, temperature of larval development and level of larval nutrition, by making measurements of thorax length and wing length of adult flies is investigated.
• 2 I show that at any given time variation in body size of Drosophila buzzatii from two sites in eastern Australia is determined primarily by variation in the quality of nutrition available to larvae.
• 3 Throughout the year adult flies are consistently at least 25% smaller in volume than predicted for optimal nutrition at their predicted temperature of larval development.
• 4 Nutritional stress is therefore a year-round problem for these flies.
• 5 Measurements of adult flies emerging from individual breeding substrates (rotting cactus cladodes) show that there is substantial variation among these substrates in the nutrition available to larvae.
• 6 This method will allow study of spatial and temporal variation in the temperature of larval substrates and in the nutritional resources available to flies in natural populations.

     

Wingbeat frequency, temperature and body size in bees and flies

ABSTRACT. This paper describes the relationship between ambient temperature and wingbeat frequency in bees and flies of different sizes, and presents new data from insects in free fight. The slope of the relationship changes with the size of the insect, and was different for insects in hovering flight compared with individuals of the same species in forward flight.     

Winter survival of age-0 smallmouth bass, <Emphasis Type=Italic>Micropterus dolomieu</Emphasis>, in north eastern lakes

We examined the winter survival of age-0 smallmouth bass,Micropterus dolomieu, in lakes at their northern limit of distribution in New Brunswick, Canada. Pre- and post-winter collections over a 3 year period suggested the smallest individuals, <50 mm total length, died during winter under ice. Experiments with wild, age-0 smallmouth bass held in lakes demonstrated a size-dependent survival where smaller individuals had greater survival with an increasing temperature of exposure, but the largest individuals had reduced survival at warmer temperatures. Survivors lost 22–54% of pre-winter energy reserves measured as ash-free dry weight, which was similar to wild individuals captured in spring. Body size at the onset of winter affects survival, but it also appears that temperature interacting with a suite of environmental and biological factors affect changes in energy use and therefore survival of age-0 smallmouth bass under ice in winter.     

Thermoregulatory abilities of Alaskan bees: effects of size, phylogeny and ecology

1. The thermoregulatory capabilities of 18 species of Alaskan bees spanning nearly two orders of magnitude of body mass were measured. Thoracic temperature, measured across the temperature range at which each species forages, was regressed against operative (environmental) temperature to determine bees' abilities to maintain relatively constant thoracic temperatures across a range of operative temperatures (thermoregulatory performance).
2. Previous studies on insect thermoregulation have compared thoracic temperature with ambient air temperature. Operative temperature, which integrates air temperature, solar radiation and effects of wind, was estimated by measuring the temperature of a fresh, dead bee in the field environment. It is suggested that this is a more accurate measure of the thermal environment experienced by the insect and also allows direct comparisons of insects under different microclimate conditions, such as in sun and shade.
3. Simple regression analysis of species and family means, and analysis of phylogenetically based independent contrasts showed thermoregulatory capability, ability to elevate thoracic temperature, and minimum thoracic temperature necessary for initiating flight all increased with body size.
4. Bumble-bees were better thermoregulators than solitary bees primarily as a consequence of their larger body size. However, their thermoregulatory abilities were slightly, but significantly, better than predicted from body size alone, suggesting an added role of pelage and/or physiology. Large solitary bees were better thermoregulators than small solitary bees apparently as a result of body-size differences, with small bees acting as thermal conformers.     

Effects of fruit set sequence and defoliation on cell number,cell size and hormone levels of tomato fruits (Lycopersicon esculentum Mill.) within a truss

Fruit size within a tomato (Lycopersicon esculentum Mill.) truss depends on both fruit position in the truss and the time of pollination among fruits. In the natural pollination sequence a difference of 5 days in the pollination of proximal and distal flowers results in significant final size differences between proximal and distal fruits. These final size differences were eliminated when all flowers were pollinated simultaneously. At anthesis proximal ovaries have higher cell numbers than distal ovaries but the cell division activity and cell enlargement in both positions was similar in the first 10 days of fruit growth. Simultaneous pollination resulted in lower cell numbers in proximal but higher cell numbers in distal fruits compared to control fruits.Hormone levels in different sized fruits were measured using radioimmunoassays. Cytokinin concentration during the cell division period indicated a possible role in the regulation of cell division. With other hormones no obvious correlations were found. The results are discussed in relation to factors determining final fruit size in tomato.