Population dynamics

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Analyses of factors influencing the population dynamics of cereal aphids and their relevance to model extensions

Analyses of factors influencing the population dynamics of cereal aphids and their relevance to model extensions

not influence the distribution of non-host alternating species S. avenae. In contrast to M. dirhodum (and S. avenae ), it seems that R. padi benefits from a close proximity between its winter and summer hosts especially in those years, when high population development on P. padus occurs. Density gradients levelled off at about 12 m distances to winter hosts (decreased abundances), and the population densities of R. padi were equal to the mean field densities. Landscape elements like hedges may cause turbulence forcing small flying insects such as aphids to land with greater frequency on the leeward side of the hedge. In 2004 however, when the population level of R. padi on P. padus was generally low, no significant differences between the population build-up were detected, either on the lee- or on the windward side. Furthermore, it seems unlikely, that the major source for the observed high numbers of R. padi settling close to the field edge was from long distance migration. According to our results, the landscape type (e.g. numbers of hedges with winter hosts in small structured landscapes) seems to be an important factor determining the size of local sources of R. padi with short distance spread, and may be included in extensions of models for predicting detailed population dynamics.
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Population dynamics and breeding patterns of Mastomys natalensis Smith 1932 in irrigated rice in eastern Tanzania

Population dynamics and breeding patterns of Mastomys natalensis Smith 1932 in irrigated rice in eastern Tanzania

4 Ilonga Agricultural Research Institute P.O. Box 33 Kilosa, Tanzania DOI: 10.5073/jka.2011.432.096 Abstract The population dynamics and breeding patterns of the Multimammate rat, Mastomys natalensis, were investigated in irrigated rice cropping systems in eastern Tanzania in 2010/ 2011. Population abundance varied with habitat and crop growth stages. In both rice fields and fallow land, the highest population peak was observed during the dry season from July to October. The results show that M. natalensis is sexually active throughout rice cropping season in the study area, although it reaches the highest level at maturity stage of crop growth. Breeding occurred in the dry and wet seasons, and suggests that it was highly influenced by the presence of a rice crop in both seasons. More juvenile individuals were recorded at transplanting stage in each season and few in the subsequent crop growth stages in all habitats. Breeding, therefore, was not seasonal and seemed not to be associated with rainfall patterns. The sex ratio of M. natalensis was not skewed to either males or females.
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Product innovation and population dynamics in the German insurance market

Product innovation and population dynamics in the German insurance market

Empirical research in organizational ecology has mainly focused on analyzing founding and mortality rates using life history data of the organizations. We try to extend this approach in our study in a number of ways. In contrast to most empirical studies in organizational ecology, we chose a population of service organizations, the development dynamics of which are rather obvious in the innovative activities of existing organizations than in founding activities. We further discuss the points of contact between the organizational ecology approach and the theory of industry life cycles and extend the analysis to the relationship between innovative activities and population dynamics. The study examines the effects of population density, former events, and organizational size and age structure in the population of property & casualty insurance companies on the number of product innovations generated. We will further develop a concept for an insurance specific industry life cycle with a non- typical maturation and degeneration phase, and discuss to what extent the concept of Maslow's pyramid of needs can have explanatory power regarding the pattern of density dynamics. This study proposes an empirical framework for evaluating the hypotheses generated on base of the organizational ecology theory and the insurance specific industry life cycle. We estimate and report specific tests of the innovation rates using the traditional approach of event history analysis based on the negative binomial model.
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Insects in forests. Assemblages, effects of tree diversity and population dynamics

Insects in forests. Assemblages, effects of tree diversity and population dynamics

Insects play an essential role in forest ecosystems, e.g., by affecting the primary production and evolution of plants. They are also a critical link between plants and higher trophic levels (Mattson 1980; Crawley 1989; 1997). Forests with their vertical stratifications (e.g., canopy and understorey) support a high diversity of insects (Gunnarsson 1990; Baines et al. 1994; Humphrey et al. 1999). This includes a high diversity of insect guilds as well as the diversity within guilds (Dajoz 2000). The relationship between insects and forests is controlled by tree- insect interactions (Lieutier 2006). In turn, tree-insect interactions are influenced by biotic (e.g., tree diversity and natural enemies) and abiotic factors, e.g., temperature and carbon dioxide (Larsson 1989; Herms & Mattson 1992; Koricheva et al. 1998). Phytophagous insects are a part of a diverse group of forest insects. On the one hand, these insects feed on leaves and can at high densities cause severe defoliation and damage to forests (Williams et al. 1991; Lovett et al. 2002). On the other hand, phytophagous insects can be beneficial to forest growth. Light defoliation assists nutrient cycling, plant population and predator-prey population dynamics (Mattson & Addy 1975; Mattson 1980). Thus, phytophagous insects play an important role in the energy flux in forest ecosystems (Mattson et al. 1975; Hammond & Miller 1998). In addition to the high ecological and economic importance, some insects such as Lepidoptera are indicator species for monitoring the conservation value of forests (Kerr et al. 1998; Brown & Freitas 2000; Kitching et al. 2000). Hence, understanding the relationship between insects and forests is a key factor for better management and conservation of insect communities and forest ecosystems.
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Essays on economic determinants of population dynamics

Essays on economic determinants of population dynamics

One of the key questions in economics concerns the reasons for development differences across countries and regions. In view of the non-monotonic dynamics of long-run devel- opment, as maintained by unified growth theories, the answer to this question is closely related to the reasons for differences in the timing of the take-off in economic and de- mographic development. The timing of the demographic transition plays a central role in this context since it is widely viewed as a prerequisite of economic development. Ac- cording to the canonical view, the demographic transition begins with a reduction in mortality that is followed, with some delay, by a decline in fertility. This marks the onset of the fertility transition, which represents the key turning point for population dynamics, education, and the transition to sustained growth. In particular, the deliberate reduc- tion in fertility allowed for intensified child rearing, increased human capital investment, and ultimately a sustained increase in incomes per capita as consequence of continuing productivity improvements (Galor and Weil, 2000; Galor, 2011). Consequently, the tran- sition from a Malthusian population regime with slowly increasing population density and living standards to a Modern Growth regime with a sustained growth in incomes that is accompanied by a decline in fertility constitutes the central building block of the mecha- nisms underlying unified growth theory. While there is widespread agreement about the role of the fertility transition for the economic take-off and ample evidence regarding the mechanics of these transitions, there is relatively little empirical work in economics that
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Life cycle and population dynamics of the calanoid copepod Pseudocalanus spp. in the Baltic Sea and North Sea

Life cycle and population dynamics of the calanoid copepod Pseudocalanus spp. in the Baltic Sea and North Sea

In the central Baltic Sea, only local impact of invertebrate predators is expected. Barz (2006) found swarms of mysids and chaetognaths in higher concentrations sporadic in the marginal areas of the Bornholm Basin, suggesting only low predatory impact on the zooplankton. The occasionally occurring scyphomedusae of Aurelia aurita inhabit mainly the upper 20 m above the thermocline during summer and do not overlap with the bulk of the P. acuspes population (Barz 2006). In the North Sea, predation on P. elongatus might play a more important role in the recruitment of Pseudocalanus due to the high number of invertebrate predators. The chaetognath Sagitta setosa removed 26-48% d -1 of the Pseudocalanus sp. population in the Gullmar Fjord (Kattegat, Sweden) (Tønnesson and Tiselius 2005). A model developed for Georges Bank suggested the summer decline of the Pseudocalanus population to be due to the combined activity of carnivorous copepods and other invertebrate predators (Davis 1984a). In both study areas the feeding of fish populations on different stages of Pseudocalanus spp. plays an important role in the Pseudocalanus population dynamics. Predation of adult sprat and herring on P. acuspes in the central Baltic Sea is suggested to largely affect its life cycle during the main reproductive period in April and May, when herring return from their spawning areas and both planktivorous predators, herring and sprat, are reported to prey on older stages of P. acuspes in the region of the halocline (Möllmann and Köster 1999, 2002, Renz and Hirche 2006, PUBLICATION I). In late winter and spring, egg production of Pseudocalanus spp. is important for establishing prey levels of recently spawned fish larvae, such as cod, in the central Baltic Sea (Hinrichsen et al. 2002) as well as in the North Sea, where the group of Pseudocalanus/Paracalanus can comprise up to 50% of the stomach content of sprat larvae (Dickmann 2005). The key role of Pseudocalanus spp. in the stock dynamics of commercially important fish is especially emphasised in the Baltic Sea (Möllmann et al. 2003, Hinrichsen et al. 2003), while the high copepod diversity of the North Sea might provide alternative food resources for predators feeding on copepods.
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Population dynamics of the Argentinean surf clamsDonax hanleyanus and Mesodesma mactroidesfrom open-Atlantic beaches off Argentina

Population dynamics of the Argentinean surf clamsDonax hanleyanus and Mesodesma mactroidesfrom open-Atlantic beaches off Argentina

Argentina has a 6,816 km long coast line 5 (Diez 2008) populated by above average numbers of humans (45.1 %, measured by the world population living in coastal areas, CIESIN 2000). The population dynamics of both surf clams were studied during alternate spring tides at (i) the beach Santa Teresita (36°32'S, 56°41'W), which is heavily influenced by mass tourism during the summer season (> 1,000 tourists 100 m -1 coastline), (ii) the beach Mar de las Pampas (37°19'S, 57°00'W), which is marginally influenced by humans (< 10 tourists 100 m -1 coastline), and (iii) the beach Faro Querandí (37°29'S, 57°07'W), which is unaffected by humans (< 0.01 angler 100 m -1 coastline) and naturally protected (pers. observ., Fig. 5b, Fig. 6). All three open ocean beaches are located on the 1,949 km long, mainly sandy, coast of the Province of Buenos Aires (Diez 2008) and are linked to each other with a north-south shoreline orientation, which is stable on a long term basis (Marcomini and López 1993). According to McLachlan`s (1980) scale for rating exposure and Short and Wright’s (1983) classifications of beach types, Santa Teresita is sheltered/dissipative, Mar de las Pampas exposed/intermediate, and Faro Querandí exposed/reflective (Fig. 6), composed of fine, medium and coarse sands with a mean particle diameter of 0.21 mm, 0.37 mm and 0.48 mm, respectively (‘Publication I’, page 79). All three beaches are, however, exposed to continuous wave action and subject to semidiurnal tides with a maximum tidal range of 1.6 m (springs tide mean 1.7 m, neaps 0.2 m). They all are affected by freshwater seepage due to the Brazil Current bringing water masses of the large-scale Río de la Plata estuary (Guerrero et al. 1997; Acha et al. 2008; Möller Jr et al. 2008). The salinity ranges between 31 and 34. The mean SST (± SE) varies between 11 ± 0.14°C in winter and 23 ± 0.21°C in summer. A full characterization of all beaches is summarised in Table 3.
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Population dynamics: general results from local analysis

Population dynamics: general results from local analysis

From the theoretical point of view population dynamics should be chaotic if chaos is in principle possible in a given system and proves to be advantageous in the evolutionary context. Regarding the effect of chaos on the evolutionary fitness of species two main lines of reasoning exist. On the one hand it is argued that the seemingly random behavior that characterizes chaos can eventually cause the extinction of species Lande (1993). On the other hand, it has been proved that chaotic fluctuations are desirable in a spatially extended environ- ment (Sol´ e and Gamarra 1998, Petrovskii et al. 2004, Allen et al. 1993). Such fluctuations increase the chance that populations survive periods of detrimen- tal conditions in isolated patches. Starting from these patches the surrounding area can be repopulated once the conditions improve. By contrast, a popula- tion with stationary or periodical dynamics is more likely to go extinct in the whole region. Following this line of reasoning chaotic dynamics can increase the chances of species survival. Consequently, it is reasonable to expect that ecological systems could evolve towards chaotic regions in parameter space if such regions exist.
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An empty land? On population dynamics and ageing in a North European periphery

An empty land? On population dynamics and ageing in a North European periphery

Population ageing, concentration and decline are three threats to the Euro- pean peripheries. The sharpening re- gional competition for human capital, the clustering of economic activities and the demographic processes may result in vicious circles of economic decline and population collapse. And in fact, most peripheries have long experienced population decrease and ageing, ten- dencies that may hit even the densest part of Europe in the foreseeable future. For once, the peripheries have been the demographic forerunner. But despite the strong trends towards decline and outmigra tion, even the most remote re- gions are not yet empty. Obviously, there are forces counteracting the trends of concentration and vicious circles. One important explanation to the relative stability in population trend may be the regional policy and many have contested the long-term sustainability of a strategy based on re gional subsidies to maintain population in the remote North. Be- ing part of the EU, the problems of the Swedish periphery may not very urgent in comparison to the situation found in economically weaker regions in eastern and southern Europe and the fi nance of the regional subsidies may be threatened. But in recent years the regional policies has changed and now the focus is more on the contribution of all regions to the national economic growth. Nevertheless, the popula tion trends in the northern pe- ripheries are rather stable and it is argued in the article that this relative stability can only be understood if the current population trends are thoroughly scruti- nised. Population dynamics is in itself a factor shaping the regional development.
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publish.UP Population dynamics of bacterial persistence

publish.UP Population dynamics of bacterial persistence

Bacterial persistence in temporally varying environments. Bacterial popula- tions tackle sudden environmental stresses by keeping a small fraction of the total pop- ulation, the persister cells, in a slow-growing but stress-tolerant phenotype state [67]. The persister cells cause a small fitness cost to the total population under growth sup- porting conditions, but provide a large benefit by withstanding antibiotic attacks. Once the growth conditions are restored, the population can recover from surviving persis- ter cells via a phenotypic switch to normal growing state. The underlying population dynamics is well described by a two state model, which considers exponential growth of the subpopulations coupled with phenotype switching between the subpopulations [4]. We analyzed this mathematical model using a simple approximation valid for small phenotype switching rates that allows to map the dynamics of subpopulation ratio to a logistic equation [97]. This indicates that under constant conditions, the effective growth rate of the persister (slow-growing) subpopulation approaches the growth rate of the normal (fast-growing) subpopulation in a logistic fashion. The steady state in the subpopulation ratio is achieved by a balance between fast-growing cells outgrowing the slow-growing ones and phenotype switching, by which the slow-growing cells are re- plenished from the fast growing cells. Therefore, a primary determinant of the persister fraction in a population is the switching rate from the normal to the persister state. A recent study, characterizing persistence in three strains (SC552, SC649, MG1655) of E. coli against three antibiotics (ampicilin, ciprofloxacin and nalidixic acid), observed this dependence. The study showed that the fractions of persisters in a population and the rate of switching from the normal to the persister state are strongly correlated across both strains and antibiotics [45].
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Inter-municipal cooperation in administrative tasks - the role of population dynamics and elections

Inter-municipal cooperation in administrative tasks - the role of population dynamics and elections

Our study builds on data from a survey among municipalities that covers 439 West- German municipalities conducted in 2015. The information from the survey – combined with data from official sources – allows us to cover a time period spanning from 2001 to 2014. In this time span, we observe a steady increase in the number of municipalities that cooperate in the field of internal administration. In line with the theory of Institutional Collective Action (see Feiock, 2007), we find IMC to be more likely in constellations where political transaction costs are low. At the same time, high administrative expenditures per capita promote IMC. We find population decline to foster IMC while municipalities do not seem to exploit complementarities resulting from divergent population dynamics. Our results show that municipalities with low cost pressure are less likely to sign IMC agreements in election years while the opposite is true when cost pressure is high. Finally, state subsidies for IMC are found to have a strong positive impact on the emergence of IMC.
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Population dynamics studies of the western corn rootworm - experiments in isolation cages

Population dynamics studies of the western corn rootworm - experiments in isolation cages

In the experiments presented here the population dynamics of Diabrotica was studied in isolation cages in the field. It is expected that the results may contribute to a review of the official measures and the further development of damage thresholds for the beetle. 2. Material and methods

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Population Dynamics - Session 2

Population Dynamics - Session 2

1 Central South University of Forestry & Technology, China, niehaiyan@126.com 2 Zhejiang University, China Life history research lies at the heart of evolutionary ecology. It studies the complex relationships in the living process, which can help us understand the evolution theory and analyze and predict population dynamics. After studying life history of plateau pika, an endemic herbivorous small mammal habituating in the Qinghai-Tibet Plateau, the following results are reported: 1. General life history features of plateau pika. 2. The similarities and differences of life history features between plateau pika and boreal pika. 3. Survival features of plateau pika in life history 4. Reproductive features of plateau pika 5. The body growth rule of plateau pika and its growth model. The growth model of juveniles is: dm/dt=6.5266•m0.75 −12.1787•m。 6. Trade-off between life history features. 7. The fitness level of plateau pika in Mammalia. A life history feature table and a life history strategy analysis table of 65 mammal species belonging to 9 Order have been compiled according to their life table data, among which the fitness indexes of 46 species have been calculated. The fitness index of plateau pika is ranked 43rd, only higher than those of bank vole (Myodes glareolus), chimpanzee (Pan troglodytes) and African elephant (Loxodonta
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Long-term population dynamics of the field vole from the Czech Republic

Long-term population dynamics of the field vole from the Czech Republic

Cyclic population dynamics of voles from central Europe have traditionally been documented using data collected in the common vole (Microtus arvalis) which is a more relevant vole to farming in this region. However, because this species does not occur in northern Europe, direct comparison of central European dynamic patterns with those in Fennoscandia has never been possible. However, this does not apply to the field vole (Microtus agrestis) whose distribution range covers much of Europe from central to northern regions, including Great Britain and Fennoscandia. Here we present long-term data on field vole dynamics from two mountain locations collected regularly twice a year by snap trapping over a period of 25 years from 1986 to 2010. The first time series data come from a study plot in the Ore Mountains (Erzgebirge) situated at the altitude of about 800 m a.s.l., the other one from that in the Giant Mountains (Riesengebirge) situated at the altitude of almost 1,100 m. There were two important features in their dynamic behaviour. First, both populations exhibit second-order dynamics with peaks about at intervals of 4 to 5 years. Second, in both of them there is a declining trend in mean density and cycle amplitude suggesting that cyclic behaviour in central European field voles is fading out in a way similar to voles in Fennoscandia. We tested for the effects of several climatic variables but the results are not consistent. These findings emphasize that population dynamics of central and northern European voles are influenced by the same mechanism which is able to operate on a large geographic scale.
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Population dynamics and within-tussock-succession in a Carex sempervirens grassland in the Swiss Alps

Population dynamics and within-tussock-succession in a Carex sempervirens grassland in the Swiss Alps

species can grow, forming small communities. However, little is known about such small-scale vegetation, especially dur- ing succession. In an abandoned subalpine pasture in the Swiss National Park, we studied population dynamics and within-tussock vegetation of Carex sempervirens in four successional grassland stages (i.e. early, young, mature and se- nescent) distinguished at community level. At population level, we observed a succession process encompassing both di- rectional and cyclic elements. In agreement with a decrease in grazing pressure and tussock vitality, similarity of the vege- tation within tussocks decreased from the early to the senescent stage. Within-tussock vegetation of the early stage was more similar to that of the young stage than to that of the mature and the senescent stage. Fuzzy ordination revealed a similar pathway of succession in C. sempervirens tussocks as observed at community level. We conclude that succes- sional transition from grassland to forest may encompass more than one C. sempervirens cycle and with each cycle floris- tic composition both inside and outside C. sempervirens tussocks will become more similar to the subsequent forest stage.
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Modelling of population dynamics of insects in any ecosystem with several distributions of insect development: A Review: Presentation

Modelling of population dynamics of insects in any ecosystem with several distributions of insect development: A Review: Presentation

Key words: Degree day, nonlinear model, distribution delay, Leslie model, chaos. Introduction Predicting the occurrence of insects in an ecosystem with a high accuracy is essential for conducting integrated pest management. These predictions require the estimation of insect development time and the variation among individuals for each life stage and species under different environmental conditions such as fluctuating temperature, variation of relative humidity, different body sizes and stages of the insects, food sources, and levels of crowding. This adds another level of complexity to models already complicated by accounting for the variable time of development (Stinner et al. 1974, Wagner et al. 1984 a and b, Briere et al. 1999, Gramig et al. 2015), variations under different temperatures (Anderson et al. 1982, Worner 1992, Regniere et al. 2012, Damos and Savopoulou- Soultani 2012, Moore and Remais 2014), variations among different growth stages and ages, and discrepancies under constant and fluctuating temperatures (Hagstrum and Milliken 1991, Nachman and Gotoh 2015). However, complexity does not assure more accuracy in all cases. Therefore, the right mathematical approach and theoretical assumptions should be developed to model population dynamics of insects with several distributions of development time. This review outlines the basic modelling methods, the disadvantages and advantages of the methods, reasons for the low accuracy of these developed models from their applications, and suggestions for future model development.
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Population dynamics and dispersal patterns of common voles (<em>Microtus arvalis</em>)

Population dynamics and dispersal patterns of common voles (<em>Microtus arvalis</em>)

experimental refuges (n=16). To measure dispersal pressure, barrier fences were installed at 10 refuges that allow immigration but prevent emigration. Since October 2009, population dynamics and dispersal rate from refuges to fields are surveyed monthly. Materials and methods

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Beech fructification and bank vole population dynamics : combined analyses of promoters of Human Puumala virus infections in Germany

Beech fructification and bank vole population dynamics : combined analyses of promoters of Human Puumala virus infections in Germany

The transmission of wildlife zoonoses to humans depends, amongst others, on complex interactions of host population ecology and pathogen dynamics within host populations. In Europe, the Puumala virus (PUUV) causes nephropathia epidemica in humans. In this study we investigated complex interrelations within the epidemic system of PUUV and its rodent host, the bank vole (Myodes glareolus). We suggest that beech fructification and bank vole abundance are both decisive factors affecting human PUUV infections. While rodent host dynamics are expected to be directly linked to human PUUV infections, beech fructification is a rather indirect predictor by serving as food source for PUUV rodent hosts. Furthermore, we examined the dependence of bank vole abundance on beech fructification. We analysed a 12-year (2001-2012) time series of the parameters: beech fructification (as food resource for the PUUV host), bank vole abundance and human incidences from 7 Fed- eral States of Germany. For the first time, we could show the direct interrelation between these three parameters involved in human PUUV epidemics and we were able to demon- strate on a large scale that human PUUV infections are highly correlated with bank vole abundance in the present year, as well as beech fructification in the previous year. By using beech fructification and bank vole abundance as predictors in one model we significantly improved the degree of explanation of human PUUV incidence. Federal State was included as random factor because human PUUV incidence varies considerably among states. Sur- prisingly, the effect of rodent abundance on human PUUV infections is less strong com- pared to the indirect effect of beech fructification. Our findings are useful to facilitate the development of predictive models for host population dynamics and the related PUUV infec- tion risk for humans and can be used for plant protection and human health protection purposes.
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Aliens attack – population dynamics and density control of American mink Neovison vison in four National Parks in Poland

Aliens attack – population dynamics and density control of American mink Neovison vison in four National Parks in Poland

Abstract American mink (Neovison vison) is a semi-aquatic species, endemic to North America, which was introduced to the wild in Europe in the 1930s. In many introduced areas, the American mink is a significant predator of waterfowl and riparian mammals, leading to a marked decrease in their density. The aim of this study is to analyze adaptation of mink in their introduced range and to determine factors affecting population dynamics and colonization rate after eradication in the 4 National Parks of Poland (Biebrza, Narew, Warta Mouth and Drawa National Park). Studies have shown that it is possible to reduce the number of mink in protected areas and gain greater knowledge of the biology and ecology of invasive species. Fieldwork and trapping were conducted in each park over 5 days twice a year (March and November 2009, 2010 and 2011). In each park, trapping took place at two sites: an experimental area [EA] (from which the mink were removed) and a control area [CA] where mink were marked and released. Live-traps were set on the banks of rivers. During the spring and summer 20 rafts were deployed (10 in the EA and 10 in the CA in each park) for population monitoring and to determine the effectiveness of mink trapping. In total 248 mink were caught (125 in the CA and 123 in the EA). The ratio of males to females was 1.6:1. Preliminary results show large differences in morphological traits and population parameters between the various national parks. The average body weight of males and females from the West of Poland was 1.35kg and 0.6kg, respectively, and from the East of Poland 2.0kg and 0.8kg, respectively. The lowest density of mink was in the Drawa (2.5 inds./10 km watercourse), and the highest was in the Narew NP (9 inds./10 km watercourse). The rate of recolonisation was related to the time since trapping and density of the mink in the NP. The frequency of mink sign found in the EA after 6 months of mink trapping was similar to that in the CA, suggesting a fast recolonisation of the eradication area in all parks. Our results underscore the need for continuing research and further analysis to underpin eradication programs, as well as monitoring and controlling populations of invasive predators in protected areas.
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OPUS 4 | Climatic effects on population dynamics and hybridization of a rare grasshopper species

OPUS 4 | Climatic effects on population dynamics and hybridization of a rare grasshopper species

Chapter III 77 Abstract Climate change and climatic extremes may affect species directly or indirectly. While direct climatic effects have been intensively studied, indirect effects, such as increasing hybridization risk, are poorly understood. We studied the impact of climate on population dynamics of a rare habitat specialist, Chorthippus montanus, and on hybridization with a sympatric habitat generalist, Chorthippus parallelus. We conducted mark-recapture studies on two sites over five years and tested for correlations with climate data and genotyped 702 individuals of two Ch. montanus generations to detect hybrids. We first tested the performance of three programs (STRUCTURE, NewHybrids, adegenet) and then accepted only hybrids detected by the two best performing programs. The highest hybridization rate (19.6%) was found in the population with lowest population size. Our results reveal that climatic extremes trigger strong population declines in the habitat specialist. This in turn, leads to increasing heterospecific encounter and may thus increase hybridization risk. Our data also show that spatiotemporal niche overlap decreases heterospecific encounter probabilities to 4.2-7.6 % compared to 20-28 % and 11-19 % calculated alone from phenology or spatial overlap, respectively. This illustrates that the combination of spatial and temporal segregation provides an effective barrier, although this function decreases with decreasing population size. Hybrids were located mainly at the edge of the specialists’ occupied habitat in areas with intermediate soil moisture conditions compared to the parental species. This confirms that climatic extremes threaten rare species both directly by reducing reproductive success and indirectly by increasing hybridization risk.
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