Extrinsic Sources Research Articles

Bridging the gap between ecology and evolution: integrating density regulation and life‐history evolution

Early demographic models of life-history evolution were formulated in a density-independent framework and saw extrinsic sources of mortality, such as predation, as the primary driving force that shaped the evolution of life-history traits. The evidence for density dependence in nature motivated theoreticians to build models that incorporated population regulation. These later generations of models acknowledge that demographic mechanisms of population regulation and extrinsic mortality interact with one another and predict a wide variety of life-history responses. Such ecologically realistic models require knowledge of the demographic traits and life-stages most affected by density. Despite the vast empirical literature characterizing population regulation, and a wealth of methods to analyze it, such mechanistic understanding is rare. Ecological experiments whereby density is manipulated can be a powerful tool to disentangle the life-history determinants of population regulation. Here we review published density-manipulation experiments and highlight how they can be coupled with existing analytical tools to extract the mechanistic information needed for evolutionary models of life histories.

Habitat heterogeneity and activity of an omnivorous ecosystem engineer control stream community dynamics

All communities vary through time. This variability originates from both intrinsic and extrinsic sources. Intrinsic sources are due to actions of organisms in a community, i.e., population dynamics and species interactions, while extrinsic variability is variability created by elements of habitat or environmental change. There is a growing appreciation that these two sources may interact, producing patterns of community variability that cannot be predicted or explained by focusing on a single source. We performed a field experiment that simultaneously manipulated trophic structure (intrinsic) and habitat heterogeneity (extrinsic) in order to examine the interaction between sources of variability in a South Carolina (USA) stream macroinvertebrate community. To manipulate trophic structure, we experimentally altered local abundances of crayfish which are keystone species and ecosystem engineers, while our manipulation of habitat was to alter stream substrate heterogeneity. We focused on two types of community variability as responses to our manipulations: aggregate variability (i.e., variability of summed species) and compositional variability (i.e., variability in relative abundances of species) by monitoring community composition through a 10-week experiment. We found that community dynamics shifted from patterns in variability indicative of synchrony (high aggregate variability + low compositional) to variability indicative of compensation (low aggregate variability + high compositional) along a gradient of increasing habitat heterogeneity. However, the shift in community dynamics only occurred when crayfish were present in the community. Supporting evidence from the experiment suggested that sediment engineering effects of crayfish acted as a community-wide perturbation in low-heterogeneity habitat creating synchronous dynamics. However, in high-heterogeneity enclosures, crayfish effects were moderated by refugia provided by a more complex substratum. The switch from synchronous to compensatory dynamics is significant since compensation stabilizes aggregate community properties and ecosystem functions while synchrony frequently exacerbates aggregate variability. Results from this experiment demonstrate that an interaction between intrinsic and extrinsic sources of variability can alter community dynamics and that such an alteration does not occur in the absence of an interaction.

Cardiac neural remodeling and its role in arrhythmogenesis

Cardiac innervation comes from both extrinsic and intrinsic sources. The extrinsic sympathetic innervation arises from the stellate ganglia and paravertebral sympathetic ganglia. The vagal nerves are sources of extrinsic parasympathetic nerves that innervate the heart. In addition to the extrinsic cardiac nervous system, there is also an extensive intrinsic cardiac nervous system1 that includes collections of ganglionated plexuses (GP). Each GP contains both sympathetic and parasympathetic neurons that are associated with complex synaptology.

Extrinsic energy sources affect hardness through depth during set of a glass-ionomer cement

To investigate the effect of various energy sources on the upper and lower surface hardness of a setting glass ionomer with various thicknesses. Cylindrical specimens (4 mm diameter by 1, 2 or 4 mm thickness) of a glass-ionomer cement were prepared with no applied energy source (control), by preheating GIC capsules in a waterbath prior to mixing, application of light with high irradiance or ultrasonic excitation with a scaler tip. The upper and lower surface hardness was measured 0.5 h, 4 h and 1 week following material mixing. The increase in temperature towards the lower surface of each specimen was monitored throughout the first 5 min of setting. No significant differences in hardness between upper and lower surfaces or varying thicknesses were identified for control and preheated samples at any post-mix time (p>0.05). At 0.5 h post-mix, the upper surface hardness of preheated, light and ultrasonic treatments was significantly increased compared with that of the control groups. Following 4 h post-mix, the overall hardness of preheated samples was significantly greater (p<0.001) than other sample groups, which were not statistically different (p=0.684). No significant differences in hardness between test groups were identified following 1 week (p>0.05). Preheating GIC capsules prior to mixing resulted in superior hardness values through depth up to and including 4 h post-mix compared with specimen surfaces treated with light irradiation or with an ultrasonic scaler tip.

Effects of annealing on the ferromagnetism and photoluminescence of Cu-doped ZnOnanowires

Room temperature ferromagnetic Cu-doped ZnO nanowires have been synthesized using thechemical vapor deposition method. By combining structural characterizations and comparativeannealing experiments, it has been found that both extrinsic (CuO nanoparticles) and intrinsic (Zn1−xCuxO nanowires) sources are responsible for the observed ferromagnetic ordering ofthe as-grown samples. As regards the former, annealing in Zn vapor led to adramatic decrease of the ferromagnetism. For the latter, a reversible switching of theferromagnetism was observed with sequential annealings in Zn vapor and oxygen ambiencerespectively, which agreed well with previous reports for Cu-doped ZnO films. Inaddition, we have for the first time observed low temperature photoluminescencechanged with magnetic properties upon annealing in different conditions, whichrevealed the crucial role played by interstitial zinc in directly mediating highTc ferromagnetism and indirectly modulating the Cu-related structured green emission viadifferent charge transfer transitions.

SEVERE COSTS OF REPRODUCTION PERSIST INANOLISLIZARDS DESPITE THE EVOLUTION OF A SINGLE-EGG CLUTCH

A central tenet of life-history theory is that investment in reproduction compromises survival. We tested for costs of reproduction in wild brown anoles (Anolis sagrei) by eliminating reproductive investment via surgical ovariectomy and/or removal of oviductal eggs. Anoles are unusual among lizards in that females lay single-egg clutches at frequent intervals throughout a lengthy reproductive season. This evolutionary reduction in clutch size is thought to decrease the physical burden of reproduction, but our results show that even a single egg significantly impairs stamina and sprint speed. Reproductive females also suffered a reduction in growth, suggesting that the cumulative energetic cost of successive clutches constrains the allocation of energy to other important functions. Finally, in each of two separate years, elimination of reproductive investment increased breeding-season survival by 56%, overwinter survival by 96%, and interannual survival by 200% relative to reproductive controls. This extreme fitness cost of reproduction may reflect a combination of intrinsic (i.e., reduced allocation of energy to maintenance) and extrinsic (i.e., increased susceptibility to predators) sources of mortality. Our results provide clear experimental support for a central tenet of life-history theory and show that costs of reproduction persist in anoles despite the evolution of a single-egg clutch.

Group-foraging is not associated with longevity in North American birds

Group-foraging is common in many animal taxa and is thought to offer protection against predators and greater foraging efficiency. Such benefits may have driven evolutionary transitions from solitary to group-foraging. Greater protection against predators and greater access to resources should reduce extrinsic sources of mortality and thus select for higher longevity according to life-history theory. I assessed the association between group-foraging and longevity in a sample of 421 North American birds. Taking into account known correlates of longevity, such as age at first reproduction and body mass, foraging group size was not correlated with maximum longevity, with and without phylogenetic correction. However, longevity increased with body mass in non-passerine birds. The results suggest that the hypothesized changes in predation risk with group size may not correlate with mortality rate in foraging birds.

Of Nutters and Doves

Under a large degree of extrinsic inflation persistence, there is a strong yet simple case for inflation targeting even if we are uncertain about many other dimensions of the economy. If inflation persistence is high and driven by extrinsic sources, even an excessively strict inflation-targeting regime is preferable to full policy discretion. Our result is entirely built on stabilization policy: long-run inflation rates are optimal under full policy discretion in our model. It is instead the medium-term dynamics of inflation expectations that render the policy response under discretion worse than inaction.

Mitochondria and the regulation of free radical damage in the eye.

Neuronal cell death can be determined by the overall level of reactive oxygen species (ROS) resulting from the combination of extrinsic sources and intrinsic production as a byproduct of oxidative phosphorylation. Key controllers of the intrinsic production of ROS are the mitochondrial uncoupling proteins (UCPs). By allowing a controlled leak of protons across the inner mitochondrial membrane activation of these proteins can decrease ROS and promote cell survival. In both primate models of Parkinson’s disease and mouse models of seizures, increased activity of UCP2 significantly increased neuronal cells survival. In the retina UCP2 is expressed in many neurons and glial cells, but was not detected in rod photoreceptors. Retinal ganglion cell survival following excitotoxic damage was much greater in animals overexpressing UCP2. Traditional Chinese medicines, such as an extract of Cistanche tubulosa, may provide benefit by altering mitochondrial metabolism.

Intrinsic and extrinsic forcing in life histories: patterns of growth and stable isotopes in male Antarctic fur seal teeth

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 388:263-272 (2009) - DOI: https://doi.org/10.3354/meps08158 Intrinsic and extrinsic forcing in life histories: patterns of growth and stable isotopes in male Antarctic fur seal teeth N. N. Hanson1,*, C. M. Wurster2, M. I. Bird2,4, K. Reid3,5, I. L. Boyd1 1Sea Mammal Research Unit, Gatty Marine Laboratory, University of St. Andrews, St. Andrews, Fife KY16 8LB, UK 2School of Geography and Geosciences, University of St. Andrews, St. Andrews, Fife KY16 9AL, UK 3British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, UK 4Present address: School of Earth and Environmental Science, James Cook University PO Box 6811, Cairns, Queensland 4870, Australia 5Present address: CCAMLR, PO Box 213, North Hobart, Tasmania 7002, Australia *Email: nnh@st-andrews.ac.uk ABSTRACT: Life-time records of the trophic sources of carbon, nitrogen and of growth rate can be generated from biogenic structures that show accretionary growth, including fish scales, whale baleen and the teeth of some animals. Records generated from individual teeth can also be combined to provide longer time series elucidating changes in environmental conditions encountered by a population. Both intrinsic (i.e. ontogenetic) and extrinsic (i.e. environmental) factors are important in modulating variation in growth and the apparent dietary sources of C and N. We used the canine teeth of a large marine predator, the male Antarctic fur seal Arctocephalus gazella from South Georgia, to investigate both intrinsic and extrinsic sources of variation. Substantial ontogenetic shifts occurred in both δ13C and δ15N values in individual teeth, indicating a change in the trophic sources of C and N as individual animals age. Over the 40 yr period from 1964 to 2005, and after statistical reduction of ontogenetic variation, we also detected long-term declines in δ13C and δ15N values, indicating that the population has become more dependent on energy from a lower trophic level. A concurrent decline in annular tooth growth may be a consequence of rapid population growth during this period. The time series of δ13C values was also inversely correlated with sea surface temperatures in the region, although isolating a causal relationship remains elusive. Our analyses suggest that both intrinsic and extrinsic sources of variation, and their interaction, must be considered from such time series data; failure to do so could result in a biased interpretation. KEY WORDS: Annulus · Dietary reconstruction · Stable isotope · Time series analysis · Southern Ocean Full text in pdf format PreviousNextCite this article as: Hanson NN, Wurster CM, Bird MI, Reid K, Boyd IL (2009) Intrinsic and extrinsic forcing in life histories: patterns of growth and stable isotopes in male Antarctic fur seal teeth. Mar Ecol Prog Ser 388:263-272. https://doi.org/10.3354/meps08158 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 388. Online publication date: August 19, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Multisensory connections of monkey auditory cerebral cortex

Functional studies have demonstrated multisensory responses in auditory cortex, even in the primary and early auditory association areas. The features of somatosensory and visual responses in auditory cortex suggest that they are involved in multiple processes including spatial, temporal and object-related perception. Tract tracing studies in monkeys have demonstrated several potential sources of somatosensory and visual inputs to auditory cortex. These include potential somatosensory inputs from the retroinsular (RI) and granular insula (Ig) cortical areas, and from the thalamic posterior (PO) nucleus. Potential sources of visual responses include peripheral field representations of areas V2 and prostriata, as well as the superior temporal polysensory area (STP) in the superior temporal sulcus, and the magnocellular medial geniculate thalamic nucleus (MGm). Besides these sources, there are several other thalamic, limbic and cortical association structures that have multisensory responses and may contribute cross-modal inputs to auditory cortex. These connections demonstrated by tract tracing provide a list of potential inputs, but in most cases their significance has not been confirmed by functional experiments. It is possible that the somatosensory and visual modulation of auditory cortex are each mediated by multiple extrinsic sources.

Magnetic states of zigzag graphene nanoribbons from first principles

The nature of the magnetic states of zigzag graphene nanoribbons (ZGNRs) was explored on the basis of density functional calculations to understand why they are apparently nonmagnetic. Our study shows that the magnetic moments of ZGNRs are destroyed by p-type or n-type carrier doping with ∼1013 carriers/cm2 per ribbon, which is close to the amount of unpaired spins that ZGNRs are expected to have. Thus the extrinsic sources of carrier doping should be removed to observe the expected magnetic character of ZGNRs.

Coherence resonance induced by the deviation of non-Gaussian noise in coupled Hodgkin–Huxley neurons

Neurons are noisy elements. Noise arises from both intrinsic and extrinsic sources. In this paper, we numerically study the effect of a particular kind of colored non-Gaussian noise (NGN), mainly of its deviation q from Gaussian noise, on the collective firing in bidirectionally coupled deterministic Hodgkin-Huxley neurons. It is found that the coefficient of variation (CV), characterizing the temporal regularity of the collective spikes, nonlinearly changes with increasing q and passes through a minimum at an intermediate optimal q where the collective spiking becomes most regular, which represents the presence of coherence resonance (CR). We also present a global view of CV as a function of q and neuron number N under various appropriate values of noise intensity. For each value of noise intensity, there is an island present in the contour plot, which sufficiently demonstrates the phenomenon of "q-induced CR." This phenomenon, termed as q-induced CR, shows that there is an optimal deviation of the NGN by which the coupled neurons may behave most periodically in time. Our results provide a novel constructive role of the deviation of the NGN in information processing and signal transduction in real neural systems.

Intrinsic and extrinsic sources of variation in the dynamics of large herbivore populations

We evaluated the relative importance of intrinsic (density-dependent) and extrinsic (density-independent) sources of resource variability in the dynamics of bighorn sheep ( Ovis canadensis Shaw, 1804) populations in southwestern USA. We tested the hypothesis that populations experiencing greater variation in forage availability are less likely to be at equilibrium density with forage supplies, and thus, would demonstrate weaker evidence of intraspecific competition. We used regression to relate population growth rate to rainfall (forage conditions) and to abundance (intraspecific competition) for 20 sheep populations, and we estimated the strength of the effects of density and rainfall for each population. Then we compared among populations to look for relationships between the strengths of rainfall and density effects and the variability in rainfall experienced by each population. Populations demonstrating a density effect were associated with environments having lower variability than those that did not. Populations showing a rainfall effect were associated with environments having a variability higher than those that lacked a rainfall effect. These findings are consistent with the hypothesis that populations experiencing higher variation in forage resources are less likely to achieve an equilibrium density with forage supplies where intraspecific competition would be a large determinant to the dynamics of that population.

Intrinsic and extrinsic sources of variation in the diets of harp and hooded seals revealed by fatty acid profiles

Individuals of different age, sex, and morphology are expected to exhibit differences in dietary niches largely owing to sexual dimorphism, ontogenetic niche shifts, and resource polymorphism. Harp ( Pagophilus groenlandicus (Erxleben, 1777)) and hooded ( Cystophora cristata (Erxleben, 1777)) seals are geographically overlapping and highly migratory predators in the North Atlantic Ocean. These species differ in their diving behaviour, with hooded seals diving deeper, longer, and more associated with the continental shelf edge and deep ocean than harp seals. We examined blubber fatty acid (FA) composition (N = 37; 93% of total FA by mass) of harp (adults N = 294; juveniles N = 232) and hooded (adults N = 118; juveniles N = 38) seals to test hypotheses about sources of intrinsic (age and sex) and extrinsic (geographic location, season, year) variations in diets. A significant difference in FA profiles suggested dietary segregation between species. We found significant effects of sex and age class on FA profiles, with these being more pronounced in the highly size-dimorphic hooded seals than in harp seals. FA profiles of both species also varied between inshore and offshore sampling locations and between prebreeding and postbreeding periods. Finally, FA profiles of harp seals differed among years, which was coincident with large changes in prey distribution and availability in the mid-1990s.

Of Nutters and Doves

Under a large degree of extrinsic inflation persistence, there is a strong yet simple case for inflation targeting even if we are uncertain about many other dimensions of the economy. If inflation persistence is high and driven by extrinsic sources, even an excessively strict inflation-targeting regime is preferable to full policy discretion. Our result is entirely built on stabilization policy: long-run inflation rates are optimal under full policy discretion in our model. It is instead the medium-term dynamics of inflation expectations that render the policy response under discretion worse than inaction.

Sulfur‐associated polioencephalomalacia in cattle grazing plants in the Family Brassicaceae

Polioencephalomalacia was diagnosed histologically in cattle from two herds on the Darling Downs, Queensland, during July-August 2007. In the first incident, 8 of 20 18-month-old Aberdeen Angus steers died while grazing pastures comprising 60%Sisymbrium irio (London rocket) and 40%Capsella bursapastoris (shepherd's purse). In the second incident, 2 of 150 mixed-breed adult cattle died, and another was successfully treated with thiamine, while grazing a pasture comprising almost 100%Raphanus raphanistrum (wild radish). Affected cattle were either found dead or comatose or were seen apparently blind and head-pressing in some cases. For both incidents, plant and water assays were used to calculate the total dietary sulfur content in dry matter as 0.62% and 1.01% respectively, both exceeding the recommended 0.5% for cattle eating more than 40% forage. Blood and tissue assays for lead were negative in both cases. No access to thiaminase, concentrated sodium ion or extrinsic hydrogen sulfide sources were identified in either incident. Below-median late summer and autumn rainfall followed by above-median unseasonal winter rainfall promoted weed growth at the expense of wholesome pasture species before these incidents.

Blowing in the (social) wind: Implications of extrinsic esteem contingencies for terror management and health.

In 4 studies, the role of extrinsic esteem contingencies in adjusting to shifting health-relevant standards when managing existential fears was examined. Study 1 demonstrated that after reminders of death, higher dispositional focus on extrinsic self-esteem contingencies predicted greater interest in tanning. Using a more domain-specific approach, Study 2 showed that, after being reminded of death, the more individuals smoke for social esteem reasons, the more compelling they find an antismoking commercial that exposes adverse social consequences of smoking. Study 3 explored how situational factors (i.e., priming a contingent relational schema) that implicate extrinsic contingencies facilitated the impact of shifting standard primes on tanning intentions after mortality salience. Finally, Study 4 found that mortality salience led to increased endorsement of exercise as a basis of self-worth when participants who derive self-esteem from extrinsic sources visualized someone who exercises. Together, these studies demonstrate that reminders of death interact with prevalent social standards to influence everyday health decisions.

How Can Hematopoietic Stem Cells and Myeloid Progenitors Become Transformed?.

DNA damage can be caused by intrinsic and extrinsic sources, and unrepaired or imprecisely repaired DNA can lead to mutagenesis, cell death, or malignant transformation. Here, we have used highly purified hematopoietic stem cells (HSC) and myeloid progenitor populations (MP: CMP & GMP) to understand how they respond to ionizing radiation (IR) and to establish how they recognize and repair damaged DNA. Our overall goal is to determine whether HSC and MP differ in their ability to deal with genotoxic stress and to identify the type of deregulations that each population requires for accumulating mutations and becoming transformed. By following their ability to form colonies in methylcellulose and to grow in liquid culture, we found that HSC are more capable of withstanding increasing doses of IR than MP. BrdU incorporation pulses revealed that irradiated HSC have an initial and transient pause in proliferation, while irradiated MP cycled faster than untreated MP. By monitoring apoptosis with AnnexinV/7AAD and cleaved caspase 3 staining, we showed that both irradiated HSC and MP have an immediate apoptotic response but that HSC quickly recover and restore low baseline levels of apoptosis while MP maintain high levels of apoptosis. These results suggest that HSC may pause cycling to repair damaged DNA while MP increase cycling to replenish cells cleared by apoptosis. At the molecular level, irradiated HSC displayed a strong and transient induction of several pro-apoptotic genes (bax, puma, noxa) but minimal change in expression of pro-survival genes, which are already high in those cells. In contrast, irradiated MP displayed minimal induction of pro-apoptotic genes (except for puma) but decreased expression of pro-survival genes, which are already low in those cells. Taken together, these results suggest that HSC can withstand genotoxic stress better than MP due to differences in the regulation of their apoptotic machinery leading to protection of HSC and elimination of MP. To monitor the ability of HSC and MP to recognize and repair damaged DNA, we used immunofluorescence techniques to study IR-induced DNA damage foci. Irradiated HSC and MP displayed similar kinetics of DNA damage recognition as monitored by the formation and resolution of gamma-H2AX and 53BP1 foci. In contrast, the kinetics of Rad51 foci – which signal the initiation of homologous recombination (HR) DNA repair – significantly differed between these populations. While Rad51 foci were immediately induced and quickly resolved in MP, very few Rad51 foci were formed in HSC up to 12 hours post-IR. Since HR only occurs during S/G2/M phases of the cell cycle, it is possible that the largely quiescent HSC can not utilize HR and instead use the more error prone DNA repair mechanism non-homologous end joining (NHEJ). At the molecular level, both HSC and MP displayed similar levels of genes associated with DNA damage recognition and repair (atm, rad50) and specific to HR (brca1), while MP display significantly lower levels of genes specifically involved in NHEJ (ku80) compared to HSC. These results indicate that both HSC and MP can recognize damaged DNA but might preferentially use different repair mechanisms. They also suggest that to become transformed and drive leukemia development, HSC might only require DNA damage, while MP might also need deregulation affecting both DNA repair mechanisms and apoptosis machinery. These findings provide insights into the mechanisms that maintain homeostatic function of hematopoietic stem and progenitor cells in normal tissues, and the deregulations that can occur during aging and cancer development. Ultimately, they could identify molecular targets to prevent therapy-related organ damage or secondary leukemia.

Student Motivational Dynamics

Background/Context Student motivation typically has been studied as it relates to extrinsic (e.g., reinforcement) or intrinsic (e.g., personal choice) sources of influence, with scant attention to sociocultural context. This article builds on a previous article in this special issue that (1) addresses the role of opportunity in the motivation of students in Grades 3–5 who live in poverty and attend schools engaged in Comprehensive School Reform (CSR) and (2) presents the results of survey measures designed to capture student understandings of school. Findings suggested that students differentiate the social (school, teacher, classmates) from the academic (math, reading) domains of school. This article explores individual differences in students’ global understandings of, and dispositions toward, school. Purpose The purpose of this study was to determine if and how students in Grades 3–5 who live in poverty and attend schools engaged in CSR differ in their understandings of, and dispositions toward, school. Research Design Students in Grades 3–5 who live in poverty and attend schools engaged in CSR completed the “The thing about my school is…” measure. Study 1 involved 464 students in spring 2004, Study 2 involved 328 students in fall 2004, and in Study 3, a subgroup of 101 participants was tracked from one school year to the next. Conclusions/Recommendations Exploratory factor analyses revealed individual differences in student dispositions toward school that refined global reports in ways that may prove amenable to motivational interventions. Findings suggest that the central motivational process for these students resides in a need for interpersonal validation in which achievement and affiliation concerns are mediated by participation-isolation tensions. These patterns also suggest the role of adaptation in motivation; participation and validation are central motivational processes for students in Grades 3–5 who cope with the challenges of poverty and mobility and who attend schools engaged in comprehensive reform.