Disentangling trophic relationships in a High Arctic tundra ecosystem through food web modeling.

Determining the manner in which food webs will respond to environmental changes is difficult because the relative importance of top-down vs. bottom-up forces in controlling ecosystems is still debated. This is especially true in the Arctic tundra where, despite relatively simple food webs, it is still unclear which forces dominate in this ecosystem. Our primary goal was to assess the extent to which a tundra food web was dominated by plant-herbivore or predator-prey interactions. Based on a 17-year (1993-2009) study of terrestrial wildlife on Bylot Island, Nunavut, Canada, we developed trophic mass balance models to address this question. Snow Geese were the dominant herbivores in this ecosystem, followed by two sympatric lemming species (brown and collared lemmings). Arctic foxes, weasels, and several species of birds of prey were the dominant predators. Results of our trophic models encompassing 19 functional groups showed that <10% of the annual primary production was consumed by herbivores in most years despite the presence of a large Snow Goose colony, but that 20-100% of the annual herbivore production was consumed by predators. The impact of herbivores on vegetation has also weakened over time, probably due to an increase in primary production. The impact of predators was highest on lemmings, intermediate on passerines, and lowest on geese and shorebirds, but it varied with lemming abundance. Predation of collared lemmings exceeded production in most years and may explain why this species remained at low density. In contrast, the predation rate on brown lemmings varied with prey density and may have contributed to the high-amplitude, periodic fluctuations in the abundance of this species. Our analysis provided little evidence that herbivores are limited by primary production on Bylot Island. In contrast, we measured strong predator-prey interactions, which supports the hypothesis that this food web is primarily controlled by top-down forces. The presence of allochthonous resources subsidizing top predators and the absence of large herbivores may partly explain the predominant role of predation in this low-productivity ecosystem.

Comorbidity of parental anxiety disorders as risk for childhood-onset anxiety in inhibited children.

OBJECTIVE: Previous work suggested that children of parents with panic disorder and agoraphobia were likely to be classified as behaviorally inhibited and that behaviorally inhibited children were likely to develop anxiety disorders. However, the factors determining which inhibited children were at risk for childhood onset of anxiety disorders remained unknown. The authors of this study hypothesized that greater anxiety loading in parents would increase the risk for anxiety disorders in children with behavioral inhibition. METHOD: Using DSM-III structured interviews, the authors examined patterns of aggregation of anxiety disorders in parents of two existing cohorts of children, one cross-sectional and clinically derived (31 children, 60 parents) and the other epidemiologically derived and longitudinal (40 children, 75 parents). Within each cohort, parents were stratified into three groups based on the presence (behavioral inhibition and anxiety) or absence (behavioral inhibition only, no behavioral inhibition and no anxiety) of behavioral inhibition and two or more anxiety disorders in their child. RESULTS: Parents of children with behavioral inhibition and anxiety, from both the clinical and nonclinical cohorts, had significantly higher rates of two or more anxiety disorders than did parents of children with behavioral inhibition only and parents of children with no behavioral inhibition and no anxiety. CONCLUSIONS: These results indicate that the presence of parental loading for anxiety disorders may help to identify the subgroup of inhibited children at very high risk for developing childhood-onset anxiety disorders.

Stable behavioral inhibition and its association with anxiety disorder.

"Behavioral inhibition to the unfamiliar" is a temperamental construct reflecting the tendency to be shy, timid, and constrained in novel situations. Previous work has suggested that it may be associated with anxiety disorders in children. Psychopathology was assessed in children from a nonclinical sample originally identified as behaviorally inhibited or uninhibited at 21 months and followed through 7 1/2 years. Children who remained inhibited at 4, 5 1/2 and 7 1/2 years (Stable Inhibited) had higher rates of anxiety disorders than children who were not consistently inhibited. Their parents had higher rates of multiple childhood anxiety disorders and of continuing anxiety disorder. These results suggest that the association between behavioral inhibition and anxiety disorder is accounted for by children who have stable behavioral inhibition.

Behavioral inhibition in children: a possible precursor to panic disorder or social phobia.

A biological-environmental interaction currently provides the best explanation of an anxiety disorder's evolution. In this sense, anxiety disorders are like other medical disorders for which a person may have a predisposition. Our knowledge of the evolution of anxiety disorders would be enhanced by the ability to identify those persons predisposed to anxiety and to identify such "proneness" before an anxiety disorder emerges in adulthood. We discuss the developmental aspects of panic disorder and social phobia, in particular findings suggesting that behavioral inhibition in children may be a precursor to phobic disorders in adults. Only longitudinal studies will resolve whether childhood response patterns are specifically linked to the risk of developing anxiety disorders or other psychopathology across the life cycle. In the interim, we suggest some guidelines for parents and clinicians to meet the unique needs of the inhibited child.

A high risk study of young children of parents with panic disorder and agoraphobia with and without comorbid major depression.

Using family study methodology and psychiatric assessments by blind raters, this study tested hypotheses about patterns of familial association between anxiety and depressive disorders among high risk children of clinically referred parents. The study design contrasted five groups of children defined by the presence or absence in a parent of (1) panic disorder and agoraphobia (PDAG) without comorbid major depressive disorder (MDD) (n = 14); (2) comorbid PDAG plus MDD (PDAG + MDD) (n = 25); (3) MDD without comorbid PDAG (n = 12); (4) other psychiatric disorders (n = 23); and (5) normal comparisons (n = 47). While the PDAG and PDAG + MDD groups had similarly elevated rates of anxiety disorders and MDD, offspring of MDD parents had an elevated rate of MDD but not of anxiety disorders. Among children of parents with PDAG + MDD, the presence of an anxiety disorder did not significantly increase the risk for MDD in the same child. Thus, anxiety and MDD did not cosegregate among children of PDAG parents. These findings indicate that parental PDAG, either alone or comorbidly with MDD, increases the risk for both anxiety and depressive disorders in offspring. In the absence of PDAG, however, parental MDD does not appear to place children at risk for anxiety disorders. These findings are most consistent with the hypothesis that PDAG and PDAG + MDD share common familial etiologic factors while MDD alone is an independent disorder. More studies are needed to confirm these preliminary findings as well as to identify mediating factors that influence the transition from childhood to adult anxiety disorders.

Further evidence of an association between behavioral inhibition and anxiety disorders: results from a family study of children from a non-clinical sample.

Behavioral inhibition to the unfamiliar, identifiable in early childhood and reflecting the tendency to exhibit withdrawal and excessive autonomic arousal to challenge or novelty, has been found to be prevalent in young offspring of parents with panic disorder and agoraphobia and associated with risk for anxiety disorders in these children. Using family study methodology, we now examine psychopathology in first degree relatives of children from a non-clinical longitudinal cohort identified at 21 months of age as inhibited (N = 22) or uninhibited (N = 19) and followed through the age of seven years for a study of preservation of temperamental characteristics in normal children. These assessments were compared with evaluations of the first degree relatives of 20 normal comparison children. Psychiatric assessments of parents (N = 110) and siblings (N = 72) were based on structured interviews conducted blindly to the temperamental classification of the index child. Parents of inhibited children, compared with parents of uninhibited and normal controls, had significantly higher risks for multiple (greater than or equal to 2) anxiety disorders, continuing anxiety disorders (both a childhood and adulthood anxiety disorder in the same parent), social phobia, and childhood avoidant and overanxious disorders. These findings provide additional support for the hypothesis linking behavioral inhibition with risk for anxiety disorder.

Psychiatric correlates of behavioral inhibition in young children of parents with and without psychiatric disorders.

Behavioral inhibition is a laboratory-based temperamental category by the tendency to constrict behavior in unfamiliar situations and assumed to reflect low thresholds of limbic arousal. We previously found behavioral inhibition prevalent in the offspring of parents with panic disorder and agoraphobia. In this report, we examined the psychiatric correlates of behavioral inhibition by evaluating the sample of offspring of parents with panic disorder and agoraphobia, previously dichotomized as inhibited and not inhibited, and an existing epidemiologically derived sample of children, followed by Kagan and colleagues and originally identified at 21 months of age as inhibited or uninhibited. A third group of healthy children was added for comparison. Our findings indicate that inhibited children had increased risk for multiple anxiety, overanxious, and phobic disorders. It is suggested that behavioral inhibition may be associated with risk for anxiety disorders in children.