Craig R. Allen

Ecological Resilience, Biodiversity, and Scale

ABSTRACT We describe existing models of the relationship between species diversity and ecological function, and propose a conceptual model that relates species richness, ecological resilience, and scale. We suggest that species interact with scale-dependent sets of ecological structures and processes that determine functional opportunities. We propose that ecological resilience is generated by diverse, but overlapping, function within a scale and by apparently redundant species that operate at different scales, thereby reinforcing function across scales. The distribution of functional diversity within and across scales enables regeneration and renewal to occur following ecological disruption over a wide range of scales.

Pathology and failure in the design and implementation of adaptive management

The conceptual underpinnings for adaptive management are simple; there will always be inherent uncertainty and unpredictability in the dynamics and behavior of complex ecological systems as a result non-linear interactions among components and emergence, yet management decisions must still be made. The strength of adaptive management is in the recognition and confrontation of such uncertainty. Rather than ignore uncertainty, or use it to preclude management actions, adaptive management can foster resilience and flexibility to cope with an uncertain future, and develop safe to fail management approaches that acknowledge inevitable changes and surprises. Since its initial introduction, adaptive management has been hailed as a solution to endless trial and error approaches to complex natural resource management challenges. However, its implementation has failed more often than not. It does not produce easy answers, and it is appropriate in only a subset of natural resource management problems. Clearly adaptive management has great potential when applied appropriately. Just as clearly adaptive management has seemingly failed to live up to its high expectations. Why? We outline nine pathologies and challenges that can lead to failure in adaptive management programs. We focus on general sources of failures in adaptive management, so that others can avoid these pitfalls in the future. Adaptive management can be a powerful and beneficial tool when applied correctly to appropriate management problems; the challenge is to keep the concept of adaptive management from being hijacked for inappropriate use.

The Use of Discontinuities and Functional Groups to Assess Relative Resilience in Complex Systems

It is evident when the resilience of a system has been exceeded and the system qualitatively changed. However, it is not clear how to measure resilience in a system prior to the demonstration that the capacity for resilient response has been exceeded. We argue that self-organizing human and natural systems are structured by a relatively small set of processes operating across scales in time and space. These structuring processes should generate a discontinuous distribution of structures and frequencies, where discontinuities mark the transition from one scale to another. Resilience is not driven by the identity of elements of a system, but rather by the functions those elements provide, and their distribution within and across scales. A self-organizing system that is resilient should maintain patterns of function within and across scales despite the turnover of specific elements (for example, species, cities). However, the loss of functions, or a decrease in functional representation at certain scales will decrease system resilience. It follows that some distributions of function should be more resilient than others. We propose that the determination of discontinuities, and the quantification of function both within and across scales, produce relative measures of resilience in ecological and other systems. We describe a set of methods to assess the relative resilience of a system based upon the determination of discontinuities and the quantification of the distribution of functions in relation to those discontinuities.

Body Mass Patterns Predict Invasions and Extinctions in Transforming Landscapes

ABSTRACT Scale-specific patterns of resource distribution on landscapes entrain attributes of resident animal communities such that species body-mass distributions are organized into distinct aggregations. Species within each aggregation respond to resources over the same range of scale. This discontinuous pattern has predictive power: invasive species and extinct or declining species in landscapes subject to human transformation tend to be located at the edge of body-mass aggregations (P < 0.01), which may be transition zones between distinct ranges of scale. Location at scale breaks affords species great opportunity, but also potential crisis.

Panarchy: theory and application

The concept of panarchy provides a framework that characterizes complex systems of people and nature as dynamically organized and structured within and across scales of space and time. It has been more than a decade since the introduction of panarchy. Over this period, its invocation in peer-reviewed literature has been steadily increasing, but its use remains primarily descriptive and abstract. Here, we discuss the use of the concept in the literature to date, highlight where the concept may be useful, and discuss limitations to the broader applicability of panarchy theory for research in the ecological and social sciences. Finally, we forward a set of testable hypotheses to evaluate key propositions that follow from panarchy theory.

RED IMPORTED FIRE ANT IMPACTS ON NORTHERN BOBWHITE POPULATIONS

The stability of Northern Bobwhite (Colinus virginianus) populations in Texas, where high density polygyne red imported fire ants (Solenopsis invicta) account for >50% of all (S. invicta) colonies, has been cited as a reason to repudiate impacts by this exotic species on Northern Bobwhite. We used two approaches to investigate the relationship between red imported fire ants and Northern Bobwhite. In the first approach, we used correlation analysis to compare Northern Bobwhite abundance trends, determined from Christmas Bird Count data in 15 Texas counties, before and after fire ant infestation. Before red imported fire ant infestation, no significant trend in Bobwhite abundance existed (r = -0.355, P = 0.314). After fire ant infestation, Northern Bobwhite abundance declined and was highly negatively correlated with years of infestation (r = -0.867, P < 0.001). Bob- white populations from 16 uninfested counties in Texas revealed no trend over a 27-yr (1966-1992) period (r = -0.081, P = 0.688). In the second approach, red imported fire ant populations were reduced on five 202-ha study areas in the Texas Coastal Bend; autumn Northern Bobwhite densities were monitored for 2 yr on those reduced areas and five untreated areas. By the 2nd yr, Bobwhite autumn density was higher (P = 0.028) on areas where red imported fire ants were suppressed. We concluded that polygyne red imported fire ants were negatively impacting Northern Bobwhite in this region of Texas.

Adaptive Inference for Distinguishing Credible from Incredible Patterns in Nature

Strong inference is a powerful and rapid tool that can be used to identify and explain patterns in molecular biology, cell biology, and physiology. It is effective where causes are single and separable and where discrimination between pairwise alternative hypotheses can be determined experimentally by a simple yes or no answer. But causes in ecological systems are multiple and overlapping and are not entirely separable. Frequently, competing hypotheses cannot be distinguished by a single unambiguous test, but only by a suite of tests of different kinds, that produce a body of evidence to support one line of argument and not others. We call this process “adaptive inference”. Instead of pitting each member of a pair of hypotheses against each other, adaptive inference relies on the exuberant invention of multiple, competing hypotheses, after which carefully structured comparative data are used to explore the logical consequences of each. Herein we present an example that demonstrates the attributes of adaptive inference that have developed out of a 30-year study of the resilience of ecosystems.

EFFECTS OF FIRE ANTS (HYMENOPTERA: FORMICIDAE) ON HATCHING TURTLES AND PREVALENCE OF FIRE ANTS ON SEA TURTLE NESTING BEACHES IN FLORIDA

Red imported fire ants (Solenopsis invicta Buren) have increasingly been observed in loggerhead (Caretta caretta L.) and green (Chelonia mydas L.) sea turtle nests in Florida, and in the nests of freshwater turtles. They may be attracted to the disturbance, mucous and moisture associated with turtle nesting and establish foraging tunnels into turtle nests shortly after egg-laying, thus increasing the vulnerability of hatchlings to fire ant predation. We conducted experiments on a freshwater turtle (Pseudemys nelsoni Carr) to determine the potential impacts of S. invicta on turtle hatchlings. Over 70% of hatchlings were killed by S. invicta during pipping or shortly after hatching. To determine the extent of S. invicta infestation of sea turtle nesting beaches, we sampled known nesting beaches throughout the state of Florida. Beach surveys indicated that S. invicta are present and often abundant on most beaches and dunes along the Florida coast.

Understanding protected area resilience: a multi‐scale, social‐ecological approach

Protected areas (PAs) remain central to the conservation of biodiversity. Classical PAs were conceived as areas that would be set aside to maintain a natural state with minimal human influence. However, global environmental change and growing cross-scale anthropogenic influences mean that PAs can no longer be thought of as ecological islands that function independently of the broader social-ecological system in which they are located. For PAs to be resilient (and to contribute to broader social-ecological resilience), they must be able to adapt to changing social and ecological conditions over time in a way that supports the long-term persistence of populations, communities, and ecosystems of conservation concern. We extend Ostroms social-ecological systems framework to consider the long-term persistence of PAs, as a form of land use embedded in social-ecological systems, with important cross-scale feedbacks. Most notably, we highlight the cross-scale influences and feedbacks on PAs that exist from the local to the global scale, contextualizing PAs within multi-scale social-ecological functional landscapes. Such functional landscapes are integral to understand and manage individual PAs for long-term sustainability. We illustrate our conceptual contribution with three case studies that highlight cross-scale feedbacks and social-ecological interactions in the functioning of PAs and in relation to regional resilience. Our analysis suggests that while ecological, economic, and social processes are often directly relevant to PAs at finer scales, at broader scales, the dominant processes that shape and alter PA resilience are primarily social and economic.

Panarchy: Discontinuities Reveal Similarities in the Dynamic System Structure of Ecological and Social Systems

In this paper, we review the empirical evidence of discontinuous distributions in complex systems within the context of panarchy theory and discuss the significance of discontinuities for understanding emergent properties such as resilience. Over specific spatial-temporal scale ranges, complex systems can configure in a variety of regimes, each defined by a characteristic set of self-organized structures and processes. A system may remain within a regime or dramatically shift to another regime. Understanding the drivers of regime shifts has provided critical insight into system structure and resilience. Although analyses of regime shifts have tended to focus on the system level, new evidence suggests that the same system behaviors operate within scales. In essence, complex systems exhibit multiple dynamic regimes nested within the larger system, each of which operates at a particular scale. Discrete size classes observed in variables in complex systems are evidence of these multiple regimes within complex systems, and the discontinuities between size classes indicate changes in scale.