1 We examined the validity of classifying tree species as early, mid-, or late-successional based on age and height-growth rates, by comparing the age and height-growth rates of trees in the boreal ...forest. 2 Age was first examined using the traditional method of coring 30 cm above the root collar; then dendrochronology was used to locate the root collar and missing annual growth rings. Traditional ageing differentially underestimates tree age; species classified as early successional (Populus tremuloides, Betula papyrifera, and Pinus banksiana) are less severely underestimated than those classified as mid- and late-successional (Picea glauca, Picea mariana, and Abies balsamea) (0-11 vs. 0-43 years), and also have relatively fewer locally missing growth rings. Ageing at the root collar shows that all tree species recruit within 5-10 years after fire and age cannot therefore be used to determine successional status. 3 Mean time taken to grow to each 1-m increment from the root collar was estimated for each species. Species classified as early successional have relatively higher growth rates between the root collar and the first metre; they are therefore less severely underestimated when aged above the root collar, explaining why they often appear older than species classified as mid- and late-successional. The lack of species differences above 1 m means that height-growth rates cannot be used to classify these tree species as early, mid-, or late-successional. 4 In the boreal forest of Saskatchewan, the rapid recruitment of all tree species after fire, and the short fire cycle mean that the forest dynamics between catastrophic wildfires are driven primarily by the mortality rates of each species.
The stable isotope compositions of biologically precipitated apatite in bone, teeth, and scales are widely used to obtain information on the diet, behavior, and physiology of extinct organisms and to ...reconstruct past climate. Here we report the application of a new type of geochemical measurement to bioapatite, a "clumped-isotope" paleothermometer, based on the thermodynamically driven preference for (13)C and (18)O to bond with each other within carbonate ions in the bioapatite crystal lattice. This effect is dependent on temperature but, unlike conventional stable isotope paleothermometers, is independent from the isotopic composition of water from which the mineral formed. We show that the abundance of (13)C-(18)O bonds in the carbonate component of tooth bioapatite from modern specimens decreases with increasing body temperature of the animal, following a relationship between isotope "clumping" and temperature that is statistically indistinguishable from inorganic calcite. This result is in agreement with a theoretical model of isotopic ordering in carbonate ion groups in apatite and calcite. This thermometer constrains body temperatures of bioapatite-producing organisms with an accuracy of 1-2 degrees C. Analyses of fossilized tooth enamel of both Pleistocene and Miocene age yielded temperatures within error of those derived from similar modern taxa. Clumped-isotope analysis of bioapatite represents a new approach in the study of the thermophysiology of extinct species, allowing the first direct measurement of their body temperatures. It will also open new avenues in the study of paleoclimate, as the measurement of clumped isotopes in phosphorites and fossils has the potential to reconstruct environmental temperatures.
•The long term effects of failure of passive transfer of immunity (FPT) were investigated on pasture-based New Zealand dairy farms.•There were no effects of FPT on growth rates beyond 12 months of ...age.•There were no effects of FPT on first lactation milk production.
This study examined the long-term effects of failure of passive transfer of immunity (FPT; diagnosed at 1–8 days of age) on subsequent milk production, growth, reproduction, and lactation performance in dairy heifers from 12 to 36 months of age. A total of 34 farms from the Waikato and Canterbury regions of New Zealand were enrolled in 2015. Each farm was visited on three occasions during the seasonal calving period (early, middle, and late). Blood samples were collected at each visit from 20 replacement heifer calves aged between 1 and 7 days to test for FPT. These heifers (n=1879) were monitored from birth until the end of their first lactation. From 12 months of age onwards, animals were weighed at 15 and 22 months, pregnancy tested 100 days following their first mating, and milk was sampled between 3–4 times during their first lactation to determine milk volume and milk component yields. Farmers recorded any mortality events.
FPT had no effect on the odds of mortality from 12 to 22 months (P=0.57) and 12 to 34 months of age (P=0.44). There was no difference in bodyweight at 15 months (P=0.17) and 22 months of age (P=0.95), no significant difference in the odds of being diagnosed pregnant (OR 1.44; 95% CI 0.82–2.69), and no effect on milk solids (fat plus protein) yields (P=0.67). No associations were observed between serum total protein (STP) concentration and milk solids yields (P=0.22) and any other milk parameters. The data from this study indicate that FPT did not adversely affect productivity, performance, or mortality beyond 12 months of age in heifers reared in pasture-based systems.
We measured annual shell growth rates of a 374-year-old (radiometrically confirmed) bivalve mollusk specimen of
Arctica islandica (Linnaeus). This bivalve represents the oldest ever reported ...individual animal. In addition, we analyzed 1051 individual powder samples from ontogenetic years two to 40 (=
80% of the entire shell height) for isotope analyses. Oxygen and carbon isotopes exhibit clear intra-annual cycles. The highest measured carbon isotope values (on average
+
2.73‰) occurred during summer, i.e., during maximum primary productivity. The
δ
18O
aragonite-derived temperature time-series cover the period of AD 1496–1533. Temperatures calculated from oxygen isotopes ranged from 4.5 to 9.3 °C and exhibit a mean value of 6.2 °C. The latter coincides well with the 1854–2003 mean value of 6.81 °C for sea-surface temperature between February and September (=
growing season of
A. islandica). Neither oxygen nor carbon isotopes exhibit age-related, unidirectional trends. However,
δ
13C
aragonite and
δ
18O
aragonite values fluctuated at decadal periods of four, six and eight to nine years (NAO-type periods) as well as 12–14 years which may represent teleconnections to cycles in the tropical Atlantic. Annual shell growth is positively correlated to intra-annual
δ
18O
aragonite minima, i.e., warm summer temperatures (
R
2
=
0.34), and to intra-annual
δ
13C
aragonite minima (higher food supply;
R
2
=
0.42). Using a linear multiregression model, 65% of the variation in annual shell growth can be explained by summer temperature and food supply. The formation of extremely narrow annual increments coincides with major volcanic eruptions (e.g., Tambora 1815). A period of extremely variable growth occurred during the culmination of the Little Ice Age in Iceland between ca. AD 1550 and 1620. Shell growth during AD 1765–1780, however, was characterized by very little year-to-year variability, probably as the result of extremely mild climate near the end of the Little Ice Age. This study demonstrates that shells of
A. islandica provide subseasonal to multidecadal, precisely dated multi-proxies of environmental variables from marine, mid to high latitudes. Such data can be used to validate and complement climate models and further assess human impact on climate and ecosystems.
Premise of the Study
Changing climates are expected to affect the abundance and distribution of global vegetation, especially plants and lichens with an epiphytic lifestyle and direct exposure to ...atmospheric variation. The study of epiphytes could improve understanding of biological responses to climatic changes, but only if the conditions that elicit physiological performance changes are clearly defined.
Methods
We evaluated individual growth performance of the epiphytic lichen Evernia mesomorpha, an iconic boreal forest indicator species, in the first year of a decade‐long experiment featuring whole‐ecosystem warming and drying. Field experimental enclosures were located near the southern edge of the species’ range.
Key Results
Mean annual biomass growth of Evernia significantly declined 6 percentage points for every +1°C of experimental warming after accounting for interactions with atmospheric drying. Mean annual biomass growth was 14% in ambient treatments, 2% in unheated control treatments, and −9% to −19% (decreases) in energy‐added treatments ranging from +2.25 to +9.00°C above ambient temperatures. Warming‐induced biomass losses among persistent individuals were suggestive evidence of an extinction debt that could precede further local mortality events.
Conclusions
Changing patterns of warming and drying would decrease or reverse Evernia growth at its southern range margins, with potential consequences for the maintenance of local and regional populations. Negative carbon balances among persisting individuals could physiologically commit these epiphytes to local extinction. Our findings illuminate the processes underlying local extinctions of epiphytes and suggest broader consequences for range shrinkage if dispersal and recruitment rates cannot keep pace.
Ontogenetic niche theory predicts that individuals may undergo one or more changes in habitat or diet throughout their lifetime to maintain optimal growth rates, or to optimize trade-offs between ...mortality risk and growth. We combine skeletochronological and stable nitrogen isotope (δ¹⁵N) analyses of sea turtle humeri (n = 61) to characterize the growth dynamics of juvenile loggerhead sea turtles (Caretta caretta) during an oceanic-to-neritic ontogenetic shift. The primary objective of this study was to determine how ontogenetic niche theory extends to sea turtles, and to individuals with different patterns of resource use (discrete shifters, n = 23; facultative shifters n = 14; non-shifters, n = 24). Mean growth rates peaked at the start of the ontogenetic shift (based on change in δ¹⁵N values), but returned to pre-shift levels within 2 years. Turtles generally only experienced 1 year of relatively high growth, but the timing of peak growth relative to the start of an ontogenetic shift varied among individuals (before, n = 14; during, n = 12; after, n = 8). Furthermore, no reduction in growth preceded the transition, as is predicted by ontogenetic niche theory. Annual growth rates were similar between non-transitioning turtles resident in oceanic and neritic habitats and turtles displaying alternative patterns of resource use. These results suggest that factors other than maximization of size-specific growth may more strongly influence the timing of ontogenetic shifts in logger-head sea turtles, and that alternative patterns of resource use may have limited influence on somatic growth and age at maturation in this species.
Background Ecologists fiercely debate the role of soil conditions and fire regimes in controlling forest – savanna boundaries. A prominent component of this debate centres on the plausibility and ...existence of fire-mediated alternative stable state dynamics (FMASS), a model first proposed by the Tasmanian ecologist WD Jackson in 1968. The FMASS model asserts that increased or decreased landscape fire activity, often due to human intervention, can overwhelm physical environmental (e.g. topography and edaphic factors) controls of forest and savanna mosaics, thereby creating landscape dynamism. Many FMASS models include fire-vegetation-soil interactions (FVS), in which changes in fire frequency can change soil fertility and hence tree growth. This interaction, in turn, affects the capacity offorests to recover from disturbance and long unburnt savanna to convert to forest. Scope We evaluate support for the FMASS-FVS model in the context of the dynamics of the Tasmanian forests that have recently been drawn into wider, global debates surrounding the co-occurrence of tree and treeless vegetation states. We develop a simple spatial simulation model to illuminate the difficulties in analysing landscape pattern to draw inferences about the existence of FMASS-FVS. Conclusions Our review of the Tasmanian evidence shows that FMASS-FVS cannot unambiguously explain all tracts of sedgelands in Tasmanian wet forests, and hence Tasmania should not be used as an exemplar of these theories globally. Our simulations highlight that soil sampling that targets forest boundaries risks erroneously concluding that the distribution of forest and savanna boundaries is decoupled from edaphic factors. We describe a structured methodological pathway that can identify the role of FMASS-FVS in Tasmanian forest dynamics, and elsewhere in the world. This approach use cross-scale temporal and spatial analyses, and targeted experimental teste, to illuminate the interplay of fire, vegetation and edaphic factors in controlling tree establishment and growth and forest boundary dynamics.
An influential body of scholarship in political science has investigated the impact of economic crisis on various political outcomes. The vast majority of these studies rely on annual growth rates ...(AGR) to specify economic crisis. I argue that this canonical approach comes with several logical shortcomings. It leads to misguided impressions of crisis severity; it makes no distinction between rapid expansion years and rapid recovery years; and it disregards the financial dimension of economic crises. I present and discuss three alternative approaches of measuring economic crisis, imported from economics: economic shocks, economic slumps, and measures of financial crises. Examples from the regime instability literature demonstrate that these alternative crisis measurements provide results that are theoretically more nuanced and empirically more robust. On this basis, the article encourages researchers to pay more attention to the way they measure economic crisis in general and to supplement the AGR approach with alternative crisis measures in particular.
Previous research has shown that red light conditions may improve growth and decrease aggressive behaviors in chickens and turkeys; however, more recent studies suggest that blue–green light may ...improve production of broilers over red light. To date, no research has been conducted to examine whether different wavelengths of light have an impact on production in the Pekin duck. To determine this, we raised Pekin ducks under aviary conditions that were similar to standard commercial barns. The ducks were kept in 3 different pens: red light (approximately 625 nm), blue light (approximately 425 nm), and white light. Light sources in each pen were standardized to produce a peak energy at 1.6 × 103 μM photons/m2/s at the level of the ducks’ heads. Ducks were given ad libitum access to water and commercial duck diet, and were housed on pine shavings at a density of 0.43 m2/duck. Ducks were evaluated weekly for BW and condition and a subjective measure of the duck's anxiety levels was determined. We found that ducks housed under blue light had significantly (P < 0.01) reduced BW at every age until the end of the study (processing age; 35 d). Unlike ducks housed under red or white light, ducks housed in the blue pen showed a higher level of anxiety; while evaluators were in the pen a majority of them began panting, they were much less inquisitive than other ducks, they took longer to exhibit normal social behavior once evaluation was completed, and they frequently “swarmed” when no people were present. There were no differences in any measurements between the red and white-lighted pens. These data suggest that unlike the chicken, blue lights may be inappropriate for raising Pekin ducks in a commercial setting.
Species of the genus
Wolffia
(duckweed) are harvested from natural water bodies in many countries for human consumption. Relative growth rates (RGR) of 25 clones (ecotypes) representing all 11 ...species of the genus
Wolffia
were investigated under standardized laboratory conditions in search for potential candidates for production of
Wolffia
biomass at a biotechnological scale. This is the first report of large-scale screening of physiological properties of
Wolffia
species. Large differences in RGR of different clones were detected, e.g., in
Wolffia globosa
. Interestingly, intraspecific differences, i.e., at the level of clones are much higher than differences between species. Rate of photosynthesis (oxygen production in light) and respiration (oxygen consumption in dark) in clones of
W. globosa
, measured under standardized conditions, are in positive correlation with their respective RGR. Higher rate of photosynthesis seems to be a determining factor for higher RGR. The RGR of the first available axenic clone of the re-discovered species,
Wolffia microscopica
(clone 2005), depends strongly on the nutrient medium used, in contrast to other investigated species. This clone of
W. microscopica
has a doubling time of 29.3 h and represents the fastest growing flowering plant known till date.
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