Search results for " dependence"
showing 10 items of 2018 documents
Harvesting‐induced population fluctuations?
2003
It has recently been shown that damped endogenous dynamics is a common feature in Finnish grouse species; In this paper, we demonstrate that time-variant harvesting may turn damped dynamics to quasi-periodic fluctuations. Exploited populations, e.g. grouse, may therefore fluctuate more than expected if we do not manage to keep the harvest fraction constant over time. However, the harvest fraction of Finnish grouse varies with the phase of the cycle. Such a harvesting strategy could potentially change the periodicity of the fluctuations, as can a threshold harvest strategy where a constant fraction is harvested above a density threshold. The two non-linear harvesting strategies investigated …
Scale dependence of species–area relationships is widespread but generally weak in Palaearctic grasslands
2021
Questions: Species–area relationships (SARs) are fundamental for understanding biodiversity patterns and are generally well described by a power law with a constant exponent z. However, z-values sometimes vary across spatial scales. We asked whether there is a general scale dependence of z-values at fine spatial grains and which potential drivers influence it. Location: Palaearctic biogeographic realm. Methods: We used 6,696 nested-plot series of vascular plants, bryophytes and lichens from the GrassPlot database with two or more grain sizes, ranging from 0.0001 m² to 1,024 m² and covering diverse open habitats. The plots were recorded with two widespread sampling approaches (rooted presenc…
GrassPlot – a database of multi-scale plant diversity in Palaearctic grasslands
2018
GrassPlot is a collaborative vegetation-plot database organised by the Eurasian Dry Grassland Group (EDGG) and listed in the Global Index of Vegetation-Plot Databases (GIVD ID EU-00-003). GrassPlot collects plot records (relevés) from grasslands and other open habitats of the Palaearctic biogeographic realm. It focuses on precisely delimited plots of eight standard grain sizes (0.0001; 0.001; ... 1,000 m²) and on nested-plot series with at least four different grain sizes. The usage of GrassPlot is regulated through Bylaws that intend to balance the interests of data contributors and data users. The current version (v. 1.00) contains data for approximately 170,000 plots of different sizes a…
Predator–vole interactions in northern Europe: the role of small mustelids revised
2014
The cyclic population dynamics of vole and predator communities is a key phenomenon in northern ecosystems, and it appears to be influenced by climate change. Reports of collapsing rodent cycles have attributed the changes to warmer winters, which weaken the interaction between voles and their specialist subnivean predators. Using population data collected throughout Finland during 1986–2011, we analyse the spatio-temporal variation in the interactions between populations of voles and specialist, generalist and avian predators, and investigate by simulations the roles of the different predators in the vole cycle. We test the hypothesis that vole population cyclicity is dependent on predator…
Nonlinear effects of climate on boreal rodent dynamics: mild winters do not negate high-amplitude cycles
2013
Small rodents are key species in many ecosystems. In boreal and subarctic environments, their importance is heightened by pronounced multiannual population cycles. Alarmingly, the previously regular rodent cycles appear to be collapsing simultaneously in many areas. Climate change, particularly decreasing snow quality or quantity in winter, is hypothesized as a causal factor, but the evidence is contradictory. Reliable analysis of population dynamics and the influence of climate thereon necessitate spatially and temporally extensive data. We combined data on vole abundances and climate, collected at 33 locations throughout Finland from 1970 to 2011, to test the hypothesis that warming winte…
From arctic lemmings to adaptive dynamics: Charles Elton's legacy in population ecology.
2001
We shall examine the impact of Charles S. Elton's 1924 article on periodic fluctuations in animal populations on the development of modern population ecology. We argue that his impact has been substantial and that during the past 75 years of research on multi-annual periodic fluctuations in numbers of voles, lemmings, hares, lynx and game animals he has contributed much to the contemporary understanding of the causes and consequences of population regulation. Elton was convinced that the cause of the regular fluctuations was climatic variation. To support this conclusion, he examined long-term population data then available. Despite his firm belief in a climatic cause of the self-repeating …
Fine‐grain beta diversity of Palaearctic grassland vegetation
2021
QUESTIONS: Which environmental factors influence fine-grain beta diversity of vegetation and do they vary among taxonomic groups? LOCATION: Palaearctic biogeographic realm. METHODS: We extracted 4,654 nested-plot series with at least four different grain sizes between 0.0001 m² and 1,024 m² from the GrassPlot database, covering a wide range of different grassland and other open habitat types. We derived extensive environmental and structural information for these series. For each series and four taxonomic groups (vascular plants, bryophytes, lichens, all), we calculated the slope parameter (z-value) of the power law species–area relationship (SAR), as a beta diversity measure. We tested whe…
Fine-scale population dynamics in a marine fish species inferred from dynamic state-space models
2017
1. Identifying the spatial scale of population structuring is critical for the conservation of natural populations and for drawing accurate ecological inferences. However, population studies often use spatially aggregated data to draw inferences about population trends and drivers, potentially masking ecologically relevant population sub‐structure and dynamics. 2. The goals of this study were to investigate how population dynamics models with and without spatial structure affect inferences on population trends and the identification of intrinsic drivers of population dynamics (e.g. density dependence). 3. Specifically, we developed dynamic, age‐structured, state‐space models to test differe…
Rapid response of a long-lived species to improved water and grazing management: the case of the European pond turtle (Emys orbicularis) in the Camar…
2014
7 pages; International audience; Among human activities, the effect of habitat management by grazing on population viability is ambiguous. Indeed, beneficial effects of grazing are expected by maintaining open meadows, but overgrazing is supposed to increase mortality by trampling. Grazing has been shown to negatively impact the survival of European pond turtle (Emys orbicularis) in the Camargue. Consequently, a new management plan was defined. We investigated the consequences of this management using capture-recapture methods to estimate variations of population sizes in this managed site and a control site over a 17 years period. Results show an increase of the number of adults and juveni…
An ecological multi-Level theory of competition for resources used to analyse density-dependence effects in fruit production
2014
International audience; Lescourret and Génard (2003) developed a multi-level theory of competition for resources applied to fruit production, considering that any collection of unit parts (cells or seeds in a fruit, fruits in an infructescence or in a tree...) can form a population and the population is subject to competition, whatever the level of organization. The principles of the theory are that the mass of each unit decreases when the number of units in the population increases and that the total mass of the population increases as the number of units increases until it reaches a maximum, after which it decreases. A three-parameter model based on that theory was used to analyse the lev…