12,883 research outputs found
Resilience of New Zealand indigenous forest fragments to impacts of livestock and pest mammals
A number of factors have combined to diminish ecosystem integrity in New Zealand indigenous lowland forest fragments surrounded by intensively grazed pasture. Livestock grazing, mammalian pests, adventive weeds and altered nutrient input regimes are important drivers compounding the changes in fragment structure and function due to historical deforestation and fragmentation. We used qualitative systems modelling and empirical data from Beilschmiedia tawa dominated lowland forest fragments in the Waikato Region to explore the relevance of two common resilience paradigms – engineering resilience and ecological resilience – for addressing the conservation management of forest fragments into the future. Grazing by livestock and foraging/predation by introduced mammalian pests both have direct detrimental impacts on key structural and functional attributes of forest fragments. Release from these perturbations through fencing and pest control leads to partial or full recovery of some key indicators (i.e. increased indigenous plant regeneration and cover, increased invertebrate populations and litter mass, decreased soil fertility and increased nesting success) relative to levels seen in larger forest systems over a range of timescales. These changes indicate that forest fragments do show resilience consistent with adopting an engineering resilience paradigm for conservation management, in the landscape context studied. The relevance of the ecological resilience paradigm in these ecosystems is obscured by limited data. We characterise forest fragment dynamics in terms of changes in indigenous species occupancy and functional dominance, and present a conceptual model for the management of forest fragment ecosystems
Early warning signals: The charted and uncharted territories
The realization that complex systems such as ecological communities can
collapse or shift regimes suddenly and without rapid external forcing poses a
serious challenge to our understanding and management of the natural world. The
potential to identify early warning signals that would allow researchers and
managers to predict such events before they happen has therefore been an
invaluable discovery that offers a way forward in spite of such seemingly
unpredictable behavior. Research into early warning signals has demonstrated
that it is possible to define and detect such early warning signals in advance
of a transition in certain contexts. Here we describe the pattern emerging as
research continues to explore just how far we can generalize these results. A
core of examples emerges that shares three properties: the phenomenon of rapid
regime shifts, a pattern of 'critical slowing down' that can be used to detect
the approaching shift, and a mechanism of bifurcation driving the sudden
change. As research has expanded beyond these core examples, it is becoming
clear that not all systems that show regime shifts exhibit critical slowing
down, or vice versa. Even when systems exhibit critical slowing down,
statistical detection is a challenge. We review the literature that explores
these edge cases and highlight the need for (a) new early warning behaviors
that can be used in cases where rapid shifts do not exhibit critical slowing
down, (b) the development of methods to identify which behavior might be an
appropriate signal when encountering a novel system; bearing in mind that a
positive indication for some systems is a negative indication in others, and
(c) statistical methods that can distinguish between signatures of early
warning behaviors and noise
The cultural psychology of obesity: diffusion of pathological norms from Western to East Asian societies
We examine the accelerating worldwide obesity epidemic using a mathematical model relating a cognitive hypothalamic-pituitary-adrenal axis tuned by embedding cultural context to a signal of chronic, structured, psychosocial threat. The obesity epidemic emerges as a distorted physiological image of ratcheting social pathology involving massive, policy-driven, economic and social 'structural adjustment' causing increasing individual, family, and community insecurity. The resulting, broadly developmental, disorder, while stratified by expected divisions of class, ethnicity, and culture, is nonetheless relentlessly engulfing even affluent majority populations across the globe. The progression of analogous epidemics in affluent Western and East Asian socieities is particularly noteworthy since these enjoy markedly different cultural structures known to influence even such fundamental psychophysical phenomena as change blindness. Indeed, until recently population patterns of obesity were quite different for these cultures. We attribute the entrainment of East Asian societies into the obesity epidemic to the diffusion of Western socioeconomic practices whose imposed resource uncertainties and exacerbation of social and economic divisions constitute powerful threat signals. We find that individual-oriented 'therapeutic' interventions will be largely ineffective since the therapeutic process itself (e.g. relinace on drug treatments) embodies the very threats causing the epidemic
Indigenous social and economic adaptations in northern Alaska as measures of resilience
I explored one aspect of social-ecological change in the context of an Alaskan human-Rangifer system, with the goal of
understanding household adaptive responses to perturbations when there are multiple forces of change at play. I focused on households
as one element of social resilience. Resilience is in the context of transition theory, in which communities are continually in a process
of change, and perturbations are key points in the transition process. This case study of Anaktuvuk Pass, Alaska, USA, contributes
to the understanding of cultural continuity and household resilience in times of rapid change by using household survey data from
1978 to 2003 to understand how households adapted to changes in the cash economy that came with oil development at the same time
as a crash in the caribou population and state-imposed limits on caribou harvests. The research illustrates that households are resilient
in the way they capture opportunities and create a new system so that elements of the old remain while parts change.Ye
Resilience, reactivity and variability : A mathematical comparison of ecological stability measures
In theoretical studies, the most commonly used measure of ecological
stability is resilience: ecosystems asymptotic rate of return to equilibrium
after a pulse-perturbation or shock. A complementary notion of growing
popularity is reactivity: the strongest initial response to shocks. On the
other hand, empirical stability is often quantified as the inverse of temporal
variability, directly estimated on data, and reflecting ecosystems response to
persistent and erratic environmental disturbances. It is unclear whether and
how this empirical measure is related to resilience and reactivity. Here, we
establish a connection by introducing two variability-based stability measures
belonging to the theoretical realm of resilience and reactivity. We call them
intrinsic, stochastic and deterministic invariability; respectively defined as
the inverse of the strongest stationary response to white-noise and to
single-frequency perturbations. We prove that they predict ecosystems worst
response to broad classes of disturbances, including realistic models of
environmental fluctuations. We show that they are intermediate measures between
resilience and reactivity and that, although defined with respect to persistent
perturbations, they can be related to the whole transient regime following a
shock, making them more integrative notions than reactivity and resilience. We
argue that invariability measures constitute a stepping stone, and discuss the
challenges ahead to further unify theoretical and empirical approaches to
stability.Comment: 35 pages, 7 figures, 2 table
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