Disease or drought: environmental fluctuations release zebra from a potential pathogen-triggered ecological trap.

When a transmission hotspot for an environmentally persistent pathogen establishes in otherwise high-quality habitat, the disease may exert a strong impact on a host population. However, fluctuating environmental conditions lead to heterogeneity in habitat quality and animal habitat preference, which may interrupt the overlap between selected and risky habitats. We evaluated spatio-temporal patterns in anthrax mortalities in a plains zebra (Equus quagga) population in Etosha National Park, Namibia, incorporating remote-sensing and host telemetry data. A higher proportion of anthrax mortalities of herbivores was detected in open habitats than in other habitat types. Resource selection functions showed that the zebra population shifted habitat selection in response to changes in rainfall and vegetation productivity. Average to high rainfall years supported larger anthrax outbreaks, with animals congregating in preferred open habitats, while a severe drought forced animals into otherwise less preferred habitats, leading to few anthrax mortalities. Thus, the timing of anthrax outbreaks was congruent with preference for open plains habitats and a corresponding increase in pathogen exposure. Given shifts in habitat preference, the overlap in high-quality habitat and high-risk habitat is intermittent, reducing the adverse consequences for the population.

Using the Maximal Entropy Modeling Approach to Analyze the Evolution of Sedentary Agricultural Societies in Northeast China.

The emergence of agriculture and the evolution of sedentary societies are among the most important processes in human history. However, although archeologists and social scientists have long been studying these processes, our understanding of them is still limited. This article focuses on the Fuxin area in present-day Liaoning province in Northeast China. A systematic archeological survey we conducted in Fuxin in recent years located sites from five successive stages of the evolution of agricultural sedentary society. We used the principles of Maximal Entropy to study changes in settlement patterns during a long-term local trajectory, from the incipient steps toward a sedentary agricultural way of life to the emergence of complex societies. Based on the detailed data collected in the field, we developed a geo-statistical model based on Maximal Entropy (MaxEnt) that characterizes the locational choices of societies during different periods. This combination of high-resolution information on the location and density of archeological remains, along with a maximal entropy-based statistical model, enabled us to chart the long-term trajectory of the interactions between human societies and their natural environment and to better understand the different stages of the transition to developed sedentary agricultural society.

Zebra migration strategies and anthrax in Etosha National Park, Namibia.

Partial seasonal migration is ubiquitous in many species. We documented this phenomenon in plains zebra (Equus burchelli) in Etosha National Park, Namibia (ENP), and provided a cost-benefit analysis as it relates to the spatial distribution of water, vegetation and endemic anthrax. This analysis draws upon two years of ENP zebra movement data that reveal two sub-populations: migrators and non-migrators. Migrators are shown to be behaviorally dominant in the way they utilize space and use water holes. We raise the possibility that the co-existence of these two groups reflects an evolutionary process, and the size of each group maintains evolutionary equilibrium.

Projecting pest population dynamics under global warming: the combined effect of inter- and intra-annual variations.

The typical short generation length of insects makes their population dynamics highly sensitive not only to mean annual temperatures but also to their intra-annual variations. To consider the combined effect of both thermal factors under global warming, we propose a modeling framework that links general circulation models (GCMs) with a stochastic weather generator and population dynamics models to predict species population responses to inter- and intra-annual temperature changes. This framework was utilized to explore future changes in populations of Bemisia tabaci, an invasive insect pest-species that affects multiple agricultural systems in the Mediterranean region. We considered three locations representing different pest status and climatic conditions: Montpellier (France), Seville (Spain), and Beit-Jamal (Israel). We produced ensembles of local daily temperature realizations representing current and future (mid-21st century) climatic conditions under two emission scenarios for the three locations. Our simulations predicted a significant increase in the average number of annual generations and in population size, and a significant lengthening of the growing season in all three locations. A negative effect was found only in Seville for the summer season, where future temperatures lead to a reduction in population size. High variability in population size was observed between years with similar annual mean temperatures, suggesting a strong effect of intra-annual temperature variation. Critical periods were from late spring to late summer in Montpellier and from late winter to early summer in Seville and Beit-Jamal. Although our analysis suggested that earlier seasonal activity does not necessarily lead to increased populations load unless an additional generation is produced, it is highly likely that the insect will become a significant pest of open-fields at Mediterranean latitudes above 40° during the next 50 years. Our simulations also implied that current predictions based on mean temperature anomalies are relatively conservative and it is better to apply stochastic tools to resolve complex responses to climate change while taking natural variability into account. In summary, we propose a modeling framework capable of determining distinct intra-annual temperature patterns leading to large or small population sizes, for pest risk assessment and management planning of both natural and agricultural ecosystems.

Behavioral changes, stress, and survival following reintroduction of Persian fallow deer from two breeding facilities.

Reintroductions often rely on captive-raised, naïve animals that have not been exposed to the various threats present in natural environments. Wild animals entering new areas are timid and invest much time and effort in antipredator behavior. On the other hand, captive animals reared in predator-free conditions and in close proximity to humans may initially lack this tendency, but can reacquire some antipredator behavior over time. We monitored the changes in antipredator-related behaviors of 16 radio-collared Persian fallow deer (Dama mesopotamica) reintroduced to the Soreq Valley in Israel from 2 breeding facilities: one heavily visited by the public (The Biblical Zoo of Jerusalem, Israel) and the other with reduced human presence (Hai-Bar Carmel, Israel). We monitored each individual for up to 200 days after release, focusing on flush and flight distance, flight mode (running or walking), and use of cover. In addition, we compared fecal corticosterone (a stress-related hormone) from samples collected from known animals in the wild to samples collected in the breeding facilities. Reintroduced individuals from both origins exhibit increased flush distance over time; flush and flight distances were larger in individuals from Hai-Bar; use of cover increased with time, but was greater in Hai-Bar Carmel animals; corticosterone levels were significantly higher in fecal samples from reintroduced animals than in samples from captive animals; and Hai-Bar Carmel animals had an 80% survival rate over the 200 days, whereas no animals from the Biblical Zoo of Jerusalem survived. Reintroduced Persian fallow deer reacquired antipredator behaviors after the release, but the process was slow (months) and differences between conditions at the breeding facilities that were seemingly benign (e.g., number of visitors and other human related activities) influenced this process and consequently affected the success of the reintroduction. Captive breeding facilities for the purpose of reintroduction should minimize anthropogenic disturbances.