Reply to comment by Jackson and Martin on “Does timber harvest influence the dynamics of marine-derived nutrients in Southeast Alaska streams?” 1Original article by Levi et al. appears in Can. J. Fish. Aquat. Sci. 68(8): 1316–1329 and is available at http://www.nrcresearchpress.com/doi/full/10.1139/f2011-067. Comment by Jackson and Martin appears in Can. J. Fish. Aquat. Sci. 69: this issue, and is available at http://www.nrcresearchpress.com/doi/full/10.1139/f2012-104.

2012 ◽  
Vol 69 (11) ◽  
pp. 1898-1901
Author(s):  
Peter S. Levi ◽  
Jennifer L. Tank ◽  
Scott D. Tiegs ◽  
Janine Rüegg ◽  
Dominic T. Chaloner ◽  
...  
Keyword(s):  
Natural Variation ◽  
Nutrient Dynamics ◽  
Sampling Design ◽  
Timber Harvest ◽  
Usda Forest Service ◽  
Southeast Alaska ◽  
Watershed Characteristics ◽  
Stream Geomorphology ◽  
Alternative Hypotheses

The stated goal of Levi et al. (2011, Can. J. Fish. Aquat. Sci. 68: 1316–1329) was to determine the influence of geomorphic complexity on the dynamics of salmon-derived nutrients. We studied seven streams in Southeast Alaska with varying degrees of historical (mid-1900s) timber harvest and, as a result, differences in stream geomorphology. In a comment on our study, Jackson and Martin (2012, Can. J. Fish. Aquat. Sci. 69: this issue) suggest that the geomorphic complexity we ascribe to timber harvest may be due to natural variation in watershed characteristics and offer alternative hypotheses. We sought to reduce the natural variation among our study streams by using a stratified sampling design (i.e., selecting reaches classified as floodplain 4 or 5 by the USDA Forest Service), but acknowledge that, as with any ecological field study, alternative hypotheses may exist to explain observed patterns in ecological responses. We maintain that our study design was sufficiently robust (i.e., 300 m reaches studied in seven streams for 3 years, totaling 21 stream-years) to draw inferences about the influence of salmon on streamwater nutrients and, secondarily, the role of geomorphic variation in mediating nutrient dynamics. Our data also support our finding that the legacy of timber harvest altered nutrient dynamics in salmon-bearing streams via alterations to stream geomorphology that were quantifiable.

scholarly journals The role of watershed characteristics, permafrost thaw, and wildfire on dissolved organic carbon biodegradability and water chemistry in Arctic headwater streams

2015 ◽  
Vol 12 (5) ◽  
pp. 4021-4056 ◽  
Author(s):  
J. R. Larouche ◽  
B. W. Abbott ◽  
W. B. Bowden ◽  
J. B. Jones
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Aquatic Ecosystems ◽  
Vegetation Type ◽  
Watershed Scale ◽  
Ecosystem Recovery ◽  
Watershed Characteristics ◽  
Stream Geomorphology ◽  
Tundra Ecosystems

Abstract. In the Alaskan Arctic, rapid climate change is increasing the frequency of disturbance including wildfire and permafrost collapse. These pulse disturbances may influence the delivery of dissolved organic carbon (DOC) to aquatic ecosystems, however the magnitude of these effects compared to the natural background variability of DOC at the watershed scale is not well known. We measured DOC quantity, composition, and biodegradability from 14 river and stream reaches (watershed sizes ranging from 1.5–167 km2) some of which were impacted by permafrost collapse (thermokarst) and fire. We found that region had a significant impact on quantity and biodegradability of DOC, likely driven by landscape and watershed characteristics such as lithology, soil and vegetation type, elevation, and glacial age. However, contrary to our hypothesis, we found that streams disturbed by thermokarst and fire did not contain significantly altered labile DOC fractions compared to adjacent reference waters, potentially due to rapid ecosystem recovery after fire and thermokarst as well as the limited spatial extent of thermokarst. Overall, biodegradable DOC ranged from 4 to 46% and contrary to patterns of DOC biodegradability in large Arctic rivers, seasonal variation in DOC biodegradability showed no clear pattern between sites, potentially related to stream geomorphology and position along the river network. While thermokarst and fire can alter DOC quantity and biodegradability at the scale of the feature, we conclude that tundra ecosystems are resilient to these types of disturbance.

Comment on “Does timber harvest influence the dynamics of marine-derived nutrients in Southeast Alaska streams?” 1Original article by Levi et al. appears in Can. J. Fish. Aquat. Sci. 68(8): 1316–1329 and is available at http://www.nrcresearchpress.com/doi/full/10.1139/f2011-067. Reply by Levi et al. appears in Can. J. Fish. Aquat. Sci. 69: this issue, and is available at http://www.nrcresearchpress.com/doi/full/10.1139/f2012-106.

2012 ◽  
Vol 69 (11) ◽  
pp. 1894-1897 ◽  
Author(s):  
C. Rhett Jackson ◽  
Douglas J. Martin
Keyword(s):  
Temporal Variability ◽  
Nutrient Dynamics ◽  
Timber Harvest ◽  
Channel Morphology ◽  
Nutrient Concentrations ◽  
Spatial And Temporal Variability ◽  
Southeast Alaska ◽  
Channel Conditions ◽  
Sample Set ◽  
Marine Derived Nutrients

Levi et al. (2011, Can. J. Fish. Aquat. Sci. 68: 1316–1329) related nutrient concentrations before, during, and after spawning, as well as various measures of channel morphology, to levels of prior timber harvest in seven watersheds on Prince of Wales Island in Southeast Alaska, USA. They assumed that single reaches of seven streams were otherwise similar and that other controls on channel morphology and nutrient dynamics could be ignored relative to the effects of prior timber harvest. In this commentary we show that the seven watersheds were not similar and that the sample set was too small to address geomorphic variability unrelated to timber harvest. Levi et al. failed to consider adequately the natural drivers of spatial and temporal variability in channel morphology and to consider stronger alternate hypotheses for observed channel conditions.

scholarly journals The role of watershed characteristics, permafrost thaw, and wildfire on dissolved organic carbon biodegradability and water chemistry in Arctic headwater streams

2015 ◽  
Vol 12 (14) ◽  
pp. 4221-4233 ◽  
Author(s):  
J. R. Larouche ◽  
B. W. Abbott ◽  
W. B. Bowden ◽  
J. B. Jones
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Aquatic Ecosystems ◽  
Vegetation Type ◽  
Watershed Scale ◽  
Ecosystem Recovery ◽  
Watershed Characteristics ◽  
Stream Geomorphology ◽  
Tundra Ecosystems

Abstract. In the Alaskan Arctic, rapid climate change is increasing the frequency of disturbance including wildfire and permafrost collapse. These pulse disturbances may influence the delivery of dissolved organic carbon (DOC) to aquatic ecosystems, however the magnitude of these effects compared to the natural background variability of DOC at the watershed scale is not well known. We measured DOC quantity, composition, and biodegradability from 14 river and stream reaches (watershed sizes ranging from 1.5–167 km2) some of which were impacted by permafrost collapse (thermokarst) and fire. We found that region had a significant impact on quantity and biodegradability of DOC, likely driven by landscape and watershed characteristics such as lithology, soil and vegetation type, elevation, and glacial age. However, contrary to our hypothesis, we found that streams disturbed by thermokarst and fire did not contain significantly altered labile DOC fractions compared to adjacent reference waters, potentially due to rapid ecosystem recovery after fire and thermokarst as well as the limited spatial extent of thermokarst. Overall, biodegradable DOC ranged from 4 to 46 % and contrary to patterns of DOC biodegradability in large Arctic rivers, seasonal variation in DOC biodegradability showed no clear pattern between sites, potentially related to stream geomorphology and position along the river network. While thermokarst and fire can alter DOC quantity and biodegradability at the scale of the feature, we conclude that tundra ecosystems are resilient to these types of disturbance.

scholarly journals Evolution and expansion of the RUNX2 QA repeat corresponds with the emergence of vertebrate complexity

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Axel H. Newton ◽  
Andrew J. Pask
Keyword(s):  
Natural Variation ◽  
Skeletal Development ◽  
Skull Shape ◽  
Morphological Novelty ◽  
Transactivation Potential ◽  
Repeat Domain ◽  
Related Transcription Factor ◽  
Mammalian Skull ◽  
Evolutionary Tuning

AbstractRunt-related transcription factor 2 (RUNX2) is critical for the development of the vertebrate bony skeleton. Unlike other RUNX family members, RUNX2 possesses a variable poly-glutamine, poly-alanine (QA) repeat domain. Natural variation within this repeat is able to alter the transactivation potential of RUNX2, acting as an evolutionary ‘tuning knob’ suggested to influence mammalian skull shape. However, the broader role of the RUNX2 QA repeat throughout vertebrate evolution is unknown. In this perspective, we examine the role of the RUNX2 QA repeat during skeletal development and discuss how its emergence and expansion may have facilitated the evolution of morphological novelty in vertebrates.

scholarly journals Family quarrels in seeds and rapid adaptive evolution in Arabidopsis

2019 ◽  
Vol 116 (19) ◽  
pp. 9463-9468 ◽  
Author(s):  
Katherine S. Geist ◽  
Joan E. Strassmann ◽  
David C. Queller
Keyword(s):  
Adaptive Evolution ◽  
Kin Selection ◽  
Conflicts Of Interest ◽  
A Priori ◽  
Flowering Plant ◽  
Rapid Adaptation ◽  
Arms Races ◽  
Evolutionary Conflict ◽  
Alternative Hypotheses

Evolutionary conflict can drive rapid adaptive evolution, sometimes called an arms race, because each party needs to respond continually to the adaptations of the other. Evidence for such arms races can sometimes be seen in morphology, in behavior, or in the genes underlying sexual interactions of host−pathogen interactions, but is rarely predicted a priori. Kin selection theory predicts that conflicts of interest should usually be reduced but not eliminated among genetic relatives, but there is little evidence as to whether conflict within families can drive rapid adaptation. Here we test multiple predictions about how conflict over the amount of resources an offspring receives from its parent would drive rapid molecular evolution in seed tissues of the flowering plant Arabidopsis. As predicted, there is more adaptive evolution in genes expressed in Arabidopsis seeds than in other specialized organs, more in endosperms and maternal tissues than in embryos, and more in the specific subtissues involved in nutrient transfer. In the absence of credible alternative hypotheses, these results suggest that kin selection and conflict are important in plants, that the conflict includes not just the mother and offspring but also the triploid endosperm, and that, despite the conflict-reducing role of kinship, family members can engage in slow but steady tortoise-like arms races.

scholarly journals Spontaneous Gac Mutants of Pseudomonas Biological Control Strains: Cheaters or Mutualists?

2011 ◽  
Vol 77 (20) ◽  
pp. 7227-7235 ◽  
Author(s):  
William W. Driscoll ◽  
John W. Pepper ◽  
Leland S. Pierson ◽  
Elizabeth A. Pierson
Keyword(s):  
Alternative Hypothesis ◽  
Natural Populations ◽  
Regulatory System ◽  
Wild Type ◽  
Content Type ◽  
The Public ◽  
Extracellular Metabolites ◽  
Mutualistic Interaction ◽  
Alternative Hypotheses

ABSTRACTBacteria rely on a range of extracellular metabolites to suppress competitors, gain access to resources, and exploit plant or animal hosts. The GacS/GacA two-component regulatory system positively controls the expression of many of these beneficial external products in pseudomonad bacteria. Natural populations often contain variants with defective Gac systems that do not produce most external products. These mutants benefit from a decreased metabolic load but do not appear to displace the wild type in nature. How could natural selection maintain the wild type in the presence of a mutant with enhanced growth? One hypothesis is that Gac mutants are “cheaters” that do not contribute to the public good, favored within groups but selected against between groups, as groups containing more mutants lose access to ecologically important external products. An alternative hypothesis is that Gac mutants have a mutualistic interaction with the wild type, so that each variant benefits by the presence of the other. In the biocontrol bacteriumPseudomonas chlororaphisstrain 30-84, Gac mutants do not produce phenazines, which suppress competitor growth and are critical for biofilm formation. Here, we test the predictions of these alternative hypotheses by quantifying interactions between the wild type and the phenazine- and biofilm-deficient Gac mutant within growing biofilms. We find evidence that the wild type and Gac mutants interact mutualistically in the biofilm context, whereas a phenazine-defective structural mutant does not. Our results suggest that the persistence of alternative Gac phenotypes may be due to the stabilizing role of local mutualistic interactions.

Holocene soil-geomorphic surfaces influence the role of salmon-derived nutrients in the coastal temperate rainforest of Southeast Alaska

Geomorphology ◽  
2011 ◽  
Vol 126 (3-4) ◽  
pp. 377-386 ◽  
Author(s):  
David V. D'Amore ◽  
Nicholas S. Bonzey ◽  
Jacob Berkowitz ◽  
Janine Rüegg ◽  
Scott Bridgham
Keyword(s):  
Temperate Rainforest ◽  
Southeast Alaska ◽  
Geomorphic Surfaces

The impact of a crisis on entrepreneurial orientation of family firms: The role of organisational decline and generational change

2021 ◽  
pp. 026624262110366
Author(s):  
Ana M Moreno-Menéndez ◽  
Unai Arzubiaga ◽  
Vanessa Díaz-Moriana ◽  
José C Casillas
Keyword(s):  
Entrepreneurial Orientation ◽  
Family Firms ◽  
Theory And Practice ◽  
Stability And Convergence ◽  
Generational Change ◽  
Entrepreneurial Behaviour ◽  
Temporal Aspects ◽  
Alternative Hypotheses ◽  
The Impact

This article critically analyses entrepreneurial orientation (EO) in family firms after a major crisis, to investigate how firms with equal initial levels of EO reach different levels over time. Based on two alternative hypotheses (stability and convergence), we analysed whether the EO of family firms remains intact, strengthens, or weakens after a crisis. Based on an examination of a database of 151 family firms collected in 2004 and 2017, our findings reveal that compared to firms with higher pre-crisis EO levels, those with lower levels saw a larger increase post crisis. Furthermore, unlike the latter group, the former was able to maintain high pre-crisis levels even after the crisis. In addition, we also we found this relationship between pre-crisis and post-crisis EO levels to be influenced by two key periodic discontinuities, namely, organisational decline and generational change contingencies. These findings advance our understanding of temporal aspects of EO and heterogeneous entrepreneurial behaviour among family firms with significant implications for both theory and practice.

scholarly journals Iridescent structural colour production in male blue-black grassquit feather barbules: the role of keratin and melanin

2009 ◽  
Vol 6 (suppl_2) ◽  
Author(s):  
Rafael Maia ◽  
João Victor O Caetano ◽  
Sônia N Báo ◽  
Regina H Macedo
Keyword(s):  
Thin Film ◽  
Natural Variation ◽  
Single Layer ◽  
Coherent Scattering ◽  
Interspecific Variation ◽  
Stray Light ◽  
Main Role ◽  
Minimum Number ◽  
Keratin Layer

Iridescent coloration plays an important role in the visual communication system of many animal taxa. It is known that iridescent structural colours result from layers of materials with different refractive indexes, which in feathers usually are keratin, melanin and air. However, the role of these materials in the production of structural iridescent coloration is still poorly documented. Despite the great interspecific variation in the organization of such structures in bird plumage, melanin layers are usually considered too opaque, suggesting its main role is to delineate the outermost keratin layer and absorb incoherently scattered stray light. We combined spectrometry, electron microscopy and thin-film optical modelling to describe the UV-reflecting iridescent colour of feather barbules of male blue-black grassquits ( Volatinia jacarina ), characterized by a keratin layer overlying a single melanin layer. Our models indicate that both the keratin and the melanin layers are essential for production of the observed colour, influencing the coherent scattering of light. The melanin layer in some barbules may be thin enough to allow interaction with the underlying keratin; however, individuals usually have, on an average, the minimum number of granules that optimizes absorbance by this layer. Also, we show that altering optical properties of the materials resulted in better-fitting models relative to the empirically measured spectra. These results add to previous findings concerning the influence of melanin in single-layer iridescence, and stress the importance of considering natural variation when characterizing such photonic structures.

scholarly journals Reproductive Success of American Kestrels: The Role of Prey Abundance and Weather

The Condor ◽  
2000 ◽  
Vol 102 (4) ◽  
pp. 814-822 ◽  
Author(s):  
Russell D. Dawson ◽  
Gary R. Bortolotti
Keyword(s):  
Reproductive Success ◽  
Natural Variation ◽  
Weather Conditions ◽  
Prey Abundance ◽  
Offspring Size ◽  
Minimum Threshold ◽  
Provisioning Behavior ◽  
American Kestrels ◽  
Parental Provisioning

Abstract We investigated how natural variation in abundance and availability of the main prey of American Kestrels (Falco sparverius), small mammals, influenced provisioning rates by parents, and offspring size and survival. Provisioning behavior of kestrels was not constrained by the abundance of food in the environment; however, the availability of food, mediated through variation in weather, appeared to significantly influence parental provisioning behavior. Moreover, variation in weather had clear effects on reproductive success because nestlings exposed to inclement weather were smaller and lighter at fledging, and less likely to survive to fledging, compared to nestlings raised during good weather conditions. Prey abundance was not related to offspring size or survival. Our results suggest American Kestrels are limited by the availability, as opposed to abundance, of food on territories. It is likely that during our study, prey abundance was above some minimum threshold necessary to support successful reproduction, and so variation in weather affected reproduction more than variation in prey abundance.

Sign in / Sign up

Export Citation Format

Share Document