No abstract

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.

Landscapes are complex ecological systems that operate over broad spatiotemporal scales. Hierarchy theory conceptualizes such systems as composed of relatively isolated levels, each operating at a distinct time and space scale. This paper explores some basic properties of scaled systems with a view toward taking advantage of the scaled structure in predicting system dynamics. Three basic properties are explored:(1) hierarchical structuring, (2) disequilibrium, and (3) metastability. These three properties lead to three conclusions about complex ecological systems. First, predictions about landscape dynamics can often be based on constraints that directly result from scaled structure. Biotic potential and environmental limits form a constraint envelope, analogous to a niche hypervolume, within which the landscape system must operate. Second, within the constraint envelope, thermodynamic and other limiting factors may produce attractors toward which individual landscapes will tend to move. Third, because of changes in biotic potential and environmental conditions, both the constraint envelope and the local attractors change through time. Changes in the constraint structure may involve critical thresholds that result in radical changes in the state of the system. An attempt is made to define measurements to predict whether a specific landscape is approaching a critical threshold.

We analyzed survival of breeding Greater Flamingos, Phoenicopterus ruber roseus, using the capture histories of 2000 breeding birds ringed as chicks and resighted at their natal colony in the Camargue, southern France. As found in previous analyses, recapture probability varied according to year, sex, and age of the bird, and annual survival was strongly affected by winter severity. However, by using a much larger data set than in earlier analyses, we detected previously nonsignificant effects. Indeed, for the first time, sex and age of the bird were found to influence annual survival probability. We tested the hypothesis that the observed sex-related difference in survival corresponded to asymmetric costs of reproduction. A model including a cost of first observed reproduction on survival in young females only provided the best fit to the data and explained the majority of the sex-related difference in survival of birds Ͻ7 yr old. Because a cost of reproduction may be partially masked by birds that have already bred undetected, we estimated the proportion of experienced females among those observed breeding for the first time. This proportion varied with the age of the birds and was used to calculate the expected cost of early recruitment. Such a cost of early reproduction may have contributed to the evolution of deferred breeding in females. Survival of experienced females was higher than that of males, with the difference being more pronounced in early age classes. Age had a significant positive effect on survival probability of birds.

Summary 1.Factors influencing post-fledging movements before the first breeding attempt were studied in individually marked greater flamingos ( Phoenicopterus ruber roseus ) born in the Camargue, southern France, between their natal area and their principal wintering grounds (Spain, Sardinia, Tunisia and France) from 1995 to 1999. 2. We tested whether post-fledging dispersal was affected by sex, age, year, body condition, body mass and tarsus length using a multistate capture-recapture modelling approach. We focused particularly on the hypothesis that increased movement probabilities were associated with good and poor body condition. Because long-distance dispersal is energetically expensive and may involve a high risk of mortality, the acquisition of a robust physical condition prior to dispersal probably plays a critical role in determining the extent to which animals disperse. At the other extreme, birds in poor condition either leave their natal area or starve, which should result in relatively high dispersal rates. 3. Movement probabilities were not sex-dependent, but were age-dependent with high movement probabilities during the first year of life (above 0·6) and low probabilities after the first year (0·055). Movement probabilities also differed between years and localities. 4. Movement probability from the natal area was related to the body condition (and body mass) of the fledglings, with a high movement probability (0·873) when juveniles were in good body condition, and a relatively lower probability (from 0·629 to 0·724) when juveniles were in poorer condition. The proportion of variability in dispersal explained by body condition and body mass were 90·9% and 63·5%, respectively. 5. Results support the hypothesis that condition affects dispersal patterns from the natal area. They also suggest that body condition and local environmental conditions during the early growth play a role in dispersal.