386 research outputs found
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Community-based Knowledge of Indigenous Vegetation in Arid African Landscapes
This article is based on comparative research conducted in three African countriesâMali, Botswana and Kenyaâbetween 2006 and 2007. The research focuses on local perceptions of biodiversity loss and land degradation in grazing pastures as a result of anthropogenic activities. We show that land degradation can be motivated by climate change, while local overuse of indigenous vegetation can lead to resource conflict. We then examine how changes in indigenous vegetation might influence the livelihood and security of local communities. In drawing key findings common to all three countries, we suggest that the sustainability of indigenous vegetation in dryland ecosystems can be maintained through seasonal mobility of herds, preservation of dry season grazing and improved livestock marketing, and that failure to do so can result in far-reaching consequences for rural communities
Desert locust populations, rainfall and climate change: insights from phenomenological models using gridded monthly data
Using autocorrelation analysis and autoregressive integrated moving average (ARIMA)modelling, we analysed a time series of the monthly number of 1° grid squares infested with desert locust Schistocerca gregaria swarms throughout the geographical range of the species from 1930â1987. Statistically significant first- and higher-order autocorrelations were found in the series. Although endogenous components captured much of the variance, adding rainfall data improved endogenous ARIMA models and resulted in more realistic forecasts. Using a square-root transformation for the locust data improved the fit. The models were only partially successful when accounting for the dramatic changes in abundance which may occur during locust upsurges and declines, in some cases successfully predicting these phenomena but underestimating their severity. Better fitting models were also produced when rainfall data were added to models of an equivalent series for desert locust hoppers (nymphs) that incorporated lagged data for locust swarms as independent variables, representing parent generations. The results are discussed in relation to predicting likely changes in desert locust dynamics with reference to potential effects of climate change
Where could catch shares prevent stock collapse?
In a widely received study (Science 321: 1678â1681) Costello and his colleagues found that catch shares give better stock persistence and higher catch for ïŹshermen. The conclusions made by Costello et al were further being supported by Grafton and McIlgrom (Marine Policy 33: 714â 719) where they suggested a framework in order to determine the costs and beneïŹts of separate ITQ management in seven Australian commonwealth ïŹsheries, and what the alternatives should be if the net beneïŹts do not justify ITQs. This raises the question why we do not see catch shares being used more often. We explore at a global scale which countries would have the potential for â and indeed do fulïŹl the conditions necessary to implement such a management strategy
The Bioeconomics of Controlling an African Rodent Pest Species
The paper treats the economy of controlling an African pest rodent, the multimammate rat, causing major damage in maize production. An ecological population model is presented and used as a basis for the economic analyses carried out at the village level using data from Tanzania. This model incorporates both density-dependent and density-independent (stochastic) factors. Rodents are controlled by applying poison, and the economic benefits depend on the income from maize production minus the costs for maize production, fertiliser and poison. We analyse how the net present value of maize production is affected by various rodent control strategies, by varying the duration and timing of rodenticide application. Our numerical results suggest that, in association with fertiliser, it is economically beneficial to control the rodent population. In general the most rewarding duration of controlling the rodent population is 3-4 months every year, and especially at the end of the dry season/beginning of rainy season. The paper demonstrates that changing from todays practice of symptomatic treatment when heavy rodent damage is noticed to a practice where the calendar is emphasised, may substantially improve the economic conditions for the maize producing farmers. This main conclusion is quite robust and not much affected by changing prices and costs of the maize production.bio-economics; pest control; multimammate rat; crop production
Optimal age- and gear-specific harvesting policies for North-East Arctic cod
We examine optimal harvest policies in a multi-cohort, multi-gear bioeconomic model of North-East Arctic cod (Gadus morhua) which includes cannibalism and contains broader ecosystem effects. By controlling the selectivity of the different fishing equipment, we can partially target different age cohorts. We show that current gear selectivity implies that the wrong fish are targeted. Optimization shifts the exploitation pattern towards older and heavier fish. This increases the harvested biomass while reducing the number of fish removed from the ocean. The result is a much more robust and abundant cod stock with an age/size distribution closer to the stocks natural state. We optimize the Net Present Value (NPV) generated by the fishery by letting effort and selectivity be the control variables and find that NPV may be more than doubled, even when only gear selectivity or harvest effort is allowed to vary. (141 words
Non-cooperative exploitation of multi-cohort fisheries â the role of gear selectivity in the North-East Arctic cod fishery
North-East Arctic cod is shared by Russia and Norway. Taking its multi-cohort structure into account, how would optimal management look like? How would non-cooperative exploitation limit the obtainable proïŹts? To which extent could the strategic situation explain todayâs over- harvesting? Simulation of a detailed bio-economic model reveals that the mesh size should be signiïŹcantly increased, resulting not only in a doubling of economic gains, but also in a biologi- cally healthier age-structure of the stock. The Nash Equilibrium is close to the current regime.
Even when eïŹort is ïŹxed to its optimal level, the non-cooperative choice of gear selectivity leads to a large dissipation of rents
The past as a lens for biodiversity conservation on a dynamically changing planet
We are in the midst of a major biodiversity crisis, with deep impacts on the functioning of ecosystems and derived benefits to people (1, 2). But we still have time to pull back. To do so, it is imperative that we learn from plantsâ and animalsâ pastactions (3, 4). Conservation biology, ecology, and paleontology all emphasize that natural systems must exhibit resilience and dynamic responses to rapid environmental changes (3, 5, 6). Both climate and land-use change have accelerated over thepast decades, underscoring the urgency for increased understanding and action (7â9). The cumulative effects of these disruptions are not additive or systematic; rather, they posecomplex, dynamic environmental challenges to ecological systems (see âdynamic systemsâ Table 1). With the dramatic ecological effects from climate fluctuations and increasing in stability of the fabric of life (10â12), we anticipate that biota will dramatically shift their ranges, reconfiguring ecological communities across Earthâs natural landscapes (13) (Fig. 1).Todayâs most prevalent conservation approaches focus on the maintenance of static reserves. These approaches need to be supplemented by approaches that facilitate dynamic ecological shifts using flexible strategies that involve local stake holders(14â17). In addition, given the magnitude, rates, and complex interactions of anthropogenic and climatic change occurring today, these conservation approaches must beinformed by research that spans time scales to infer likely responses (18). This special feature integrates research from across spatial and temporal scales to explore how ecosystem sand communities function dynamically to respond to large scale environmental change, highlighting proposed solutions for conserving biodiversity on a rapidly changing planetFil: MacGuire, Jenny L.. Georgia Institute of Techology; Estados UnidosFil: Michelle Lawing, A.. Georgia Institute of Techology; Estados UnidosFil: DĂaz, Sandra Myrna. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto Multidisciplinario de BiologĂa Vegetal. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas FĂsicas y Naturales. Instituto Multidisciplinario de BiologĂa Vegetal; ArgentinaFil: Stenseth, Nils Chr. University of Oslo; Noruega. International Union of Biological Sciences; Franci
Resilience of the trophic cascades in the Black Sea and Baltic Sea regime shifts
The Black Sea and the Baltic Sea are two European lake-like marine systems where regime shifts have occurred. Both ecosystems show similar features and hold comparable long-term records for the main food web components and external pressures. Here we analyse Black Sea and Baltic Sea multi-trophic time series applying the same statistical tool, which allowed us to characterize tipping points and quantify the main dynamics ruling each regime phase. In both systems a trophic cascade, consequence of overfishing, drove a shift between regimes. This work focuses on the robustness of this ecological mechanism. By simulating environmental scenarios we tested whether enhanced bottom-up effects could counteract the development of the trophic cascades once these have been triggered. We found that under certain environmental settings the trophic cascade signals blur at different levels suggesting that the observed changes resulted from a combination of heavy fishing and unfavourable conditions. Through the outlook of one single methodology applied to two different but comparable systems we discuss the obstacles we may find if we are to promote a more desirable state and management measures considering synergistic effects of fishing and future climate change
Harvest-induced disruptive selection increases variance in fitness-related traits
The form of Darwinian selection has important ecological and management implications. Negative effects of harvesting are often ascribed to size truncation (i.e. strictly directional selection against large individuals) and resultant decrease in trait variability, which depresses capacity to buffer environmental change, hinders evolutionary rebound and ultimately impairs population recovery. However, the exact form of harvest-induced selection is generally unknown and the effects of harvest on trait variability remain unexplored. Here we use unique data from the Windermere (UK) long-term ecological experiment to show in a top predator (pike, Esox lucius) that the fishery does not induce size truncation but disruptive (diversifying) selection, and does not decrease but rather increases variability in pike somatic growth rate and size at age. This result is supported by complementary modelling approaches removing the effects of catch selectivity, selection prior to the catch and environmental variation. Therefore, fishing most likely increased genetic variability for somatic growth in pike and presumably favoured an observed rapid evolutionary rebound after fishery relaxation. Inference about the mechanisms through which harvesting negatively affects population numbers and recovery should systematically be based on a measure of the exact form of selection. From a management perspective, disruptive harvesting necessitates combining a preservation of large individuals with moderate exploitation rates, and thus provides a comprehensive tool for sustainable exploitation of natural resources
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