| 1. |
- Harding, Karin C., 1968, et al.
(författare)
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A unifying framework for metapopulation dynamics.
- 2002
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Ingår i: The American Naturalist. - : University of Chicago Press. - 1537-5323 .- 0003-0147. ; 160:2, s. 173-185
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Tidskriftsartikel (refereegranskat)abstract
- Many biologically important processes, such as genetic differentiation, the spread of disease, and population stability, are affected by the (natural or enforced) subdivision of populations into networks of smaller, partly isolated, subunits. Such "metapopulations" can have extremely complex dynamics. We present a new general model that uses only two functions to capture, at the metapopulation scale, the main behavior of metapopulations. We show how complex, structured metapopulation models can be translated into our generalized framework. The metapopulation dynamics arising from some important biological processes are illustrated: the rescue effect, the Allee effect, and what we term the "antirescue effect." The antirescue effect captures instances where high migration rates are deleterious to population persistence, a phenomenon that has been largely ignored in metapopulation conservation theory. Management regimes that ignore a significant antirescue effect will be inadequate and may actually increase extinction risk. Further, consequences of territoriality and conspecific attraction on metapopulation-level dynamics are investigated. The new, simplified framework can incorporate knowledge from epidemiology, genetics, and population biology in a phenomenological way. It opens up new possibilities to identify and analyze the factors that are important for the evolution and persistence of the many spatially subdivided species.
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| 2. |
- McNamara, J. M., et al.
(författare)
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Measurement error and estimates of population extinction risk
- 2004
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 7:1, s. 16-20
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Tidskriftsartikel (refereegranskat)abstract
- It is common to estimate the extinction probability for a vulnerable population using methods that are based on the mean and variance of the long-term population growth rate. The numerical values of these two parameters are estimated from time series of population censuses. However, the proportion of a population that is registered at each census is typically not constant but will vary among years because of stochastic factors such as weather conditions at the time of sampling. Here, we analyse how such sampling errors influence estimates of extinction risk and find sampling errors to produce two opposite effects. Measurement errors lead to an exaggerated overall variance, but also introduce negative autocorrelations in the time series (which means that estimates of annual growth rates tend to alternate in size). If time series data are treated properly these two effects exactly counter balance. We advocate routinely incorporating a measure of among year correlations in estimating population extinction risk.
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| 3. |
- Zetterberg, Per, et al.
(författare)
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Performance of multiple-receive multiple-transmit beamforming in WLAN-type systems under power or EIRP constraints with delayed channel estimates
- 2002
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Ingår i: IEEE 55TH VEHICULAR TECHNOLOGY CONFERENCE, VTC SPRING 2002, VOLS 1-4, PROCEEDINGS. - 0780374843 ; , s. 1906-1910
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Konferensbidrag (refereegranskat)abstract
- Downlink beamforming in a WLAN-type system employing access points and mobiles equipped with multiple antennas and associated receivers and transmitters are considered. The beamforming aims at maximizing the performance under constraints on transmit power or equivalent isotropic radiated power (EIRP). Solutions for the two constraints are derived and investigated using simulated and measured channels. Our simulation and experimental results shows that performance gains of 8-10dB when using four directional transmitter antennas and two receive antennas (as compared with a base-line one-transmit two-receive), are possible under both constraints. For simulated channels, a delay between channel estimation and use of the same channel of up to 10% of the (inverse of the) Doppler frequency only degrades performance some tenths of a dB. In our measurements, very small degradations are seen with delays of up to 130ms. The measurements were made under relatively stationary conditions with only occasionally moving people Two different strategies for updating the beamforming vectors: sounding and ping-pong, are also considered in the paper.
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