Land-use and Land-cover Changes in Pastoral Drylands: Long-term Dynamics, Economic Change, and Shifting Socioecological Frontiers in Baringo, Kenya

The ongoing fragmentation of pastoral drylands is a matter of concern throughout Africa. Using the example of rangelands in northern Baringo County, Kenya, that were under uniform pastoral use until the late twentieth century, we trace land-use and land-cover changes (LULCCs) since the 1980s. Based on ethnographic, historical, and remote sensing data, we show how bush encroachment and dryland farming have led to the increasing modification and conversion of formerly open rangelands and the diversification of livelihoods. These LULCC dynamics are related to and driven not only by internal processes of socioeconomic change (e.g., sedentarization, changing rangeland management practices, growing markets for small stock, increasing stratification and cultural differentiation) but also by ecological processes such as wildlife defaunation and ecological invasions. Based on our findings, we suggest that a socioecological approach to Kopytoff’s notion of the internal African frontier can be helpful in framing these LULCC-related dynamics.

The Minimum Environmental Perturbation Principle: A New Perspective on Niche Theory

Contemporary niche theory is a powerful conceptual framework for understanding how organisms interact with each other and with their shared environment. Here we show that a large segment of niche theory is equivalent to a Minimum Environmental Perturbation Principle (MEPP): ecosystems self-organize into a state that minimizes the impact of organisms on their environment. Different choices of environmental dynamics naturally give rise to distinct dissimilarity measures for quantifying environmental impact. The MEPP allows for the analysis of ecosystems with large numbers of species and environmental factors and provides a new avenue for analyzing ecological invasions. The MEPP also rigorously connects ecological bistability with the existence of multiple minima in a statistical-physics inspired landscapes. We show that the presence of environmental feedbacks where organisms can produce new resources in addition to depleting them violates the global MEPP. However, even in the presence of such feedbacks, a weaker, local version of the MEPP still applies in a limited region of resource space.

Introduced species are not always the enemy of conservation

This chapter tells the story of how a few biologists came to question whether non-native species were being objectively evaluated with regard to their threat to biodiversity and ecosystems. The chapter examines the criteria that are commonly used to evaluate whether species should be labeled as invasive aliens, and suggests there is merit in assessing both the positive and negative contributions of species. Because invasion biology is a heavily value-laden field in which logic does not always reign, there is resistance to considering the benefits that might accrue from non-native species. Now is the time to think hard about which species are likely to cause clear harm so that management interventions can be aimed where they are most needed, and limited resources are not squandered on relatively harmless ecological invasions.

Individual variation in dispersal associated behavioral traits of the invasive Chinese mitten crab (Eriocheir sinensis, H. Milne Edwards, 1854) during initial invasion of Lake Vänern, Sweden

Understanding and predicting species range-expansions and biological invasions is an important challenge in modern ecology because of rapidly changing environments. Recent studies have revealed that consistent within-species variation in behavior (i.e. animal personality) can be imperative for dispersal success, a key stage in the invasion process. Here we investigate the composition and correlation of two important personality traits associated with invasion success, activity and boldness, and how they are connected to sex and individual size in a newly colonised population of the Chinese mitten crab Eriocheir sinensis in Lake Vänern, Sweden. We found no effect of sex or size on behavioral expressions of E. sinensis but a clear positive correlation between boldness and activity. In addition, this study generates important baseline data for monitoring behavioral development, and thereby changing ecological impact, of an invading population over time. This has implications for predicting ecological effects of invasive species as well as for managing ecological invasions.

Wann werden gebietsfremde Gehölze invasiv? Ein methodologischer Ansatz

When do non-native species become invasive? A methodological approach The invasive behavior of non-native species in a new habitat depends on the invasiveness of the species itself on the one hand and on the invasibility of the ecosystems on the other hand. We discuss the mutual relations between the traits that foster the invasiveness of selected woody species and the invasibility of the concerned ecosystems in the light of the leading theories on ecological invasions. As examples we use selected tree species (Robinia pseudoacacia, Ailanthus altissima, Prunus serotina, Cinnamomum glandulifera), shrub species (Prunus laurocerasus, Laurus nobilis, Elaeagnus pungens) and a palm species (Trachycarpus fortunei) that are already considered to be invasive in the southern foothills of the Swiss Alps.

Personality-dependent dispersal in the invasive mosquitofish: group composition matters

Understanding/predicting ecological invasions is an important challenge in modern ecology because of their immense economical and ecological costs. Recent studies have revealed that within-species variation in behaviour (i.e. animal personality) can shed light on the invasion process. The general hypothesis is that individuals' personality type may affect their colonization success, suggesting that some individuals might be better invaders than others. We have recently shown that, in the invasive mosquitofish ( Gambusia affinis ), social personality trait was an important indicator of dispersal distance, with more asocial individuals dispersing further. Here, we tested how mean personality within a population, in addition to individual personality type, affect dispersal and settlement decisions in the mosquitofish. We found that individual dispersal tendencies were influenced by the population's mean boldness and sociability score. For example, individuals from populations with more asocial individuals or with more bold individuals are more likely to disperse regardless of their own personality type. We suggest that identifying behavioural traits facilitating invasions, even at the group level, can thus have direct applications in pest management.