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The responses of a guild of open-country birds of prey to changes in prey density were studied on a simple island habitat in southern Ontario. Numerical responses were conspicuous in all species, while functional responses were weak. Individual raptor species displayed characteristic responses, differing from others in intensity and aspects of seasonality related to breeding versus wintering. Yet a basic similarity in the form of response for all species present at any one season, and a complementarity of responses of species present through the changing seasons, resulted in an overall guild level pattern of numerical and functional response of predators to changes in prey density. The synchronous fluctuations of predator and prey densities observed are similar to those of arctic areas and unusual for the temperate regions where the study was conducted. Characteristics of the predator and prey assemblages and features of the study site were important in determining the type, the intensity, and the level (species or guild) at which the responses were exhibited.

The acute single dose oral toxicity of carbophenothion (S-4-chlorophenylthiomethyl OO-diethyl phosphorodithioate) has been determined in Canada geese (Branta canadensis), pigeons (Columba livia) and Japanese quail (Coturnix coturnix japonica). At post mortem examination gross pathological changes were observed in Canada geese and pigeons and esterase levels were determined by conventional and electrophoretic methods on extracts of liver and brain from these two species. Carbophenothion residue levels were determined in liver, brain and gizzard contents from the geese and pigeons. The overall pattern of results suggests that esterase inhibition may not be the dominant factor in carbophenothion poisoning in geese. It is suggested that a brain carbophenothion residue level of 1 part/106 is indicative of death by poisoning in geese.

This paper considers a nonlinear deterministic population model in which the death rate rises as the population grows. It is an age-dependent version of a logistic population whose growth is controlled by limited resources and is in the form of a partial differential equation with respect to time and age. We prove that the solution of our equation behaves asymptotically just like the solution of the logistic equation ${{dN} / {dt}} = N(a - bN)$ and is, therefore, globally asymptotically stable. This implies that there are no steady oscillations, and that in the long run the population size and age-structure become fixed, independent of the initial conditions. Possible applications in fish and animal population dynamics are studied.

A generalization of Bailey's general epidemic model is considered. In this generalized model, it is assumed that the probability of any particular susceptible becoming infected during the small time interval (t, t + Δt) is α(X(t))Δt + o(Δt), for some function a, where X(t) is the proportion of infected individuals in the entire population, the probability that an infected individual is infected for at least a length of time t is F(t), and recovered individuals are permanently immune from further attack. In this paper, central limit theorems are obtained for the proportion of infected individuals and the proportion of susceptibles in the entire population.

We consider a deterministic SIR model in which the daily contact rate is a constant $\alpha > 0$, the rate of an infected individual recovering from the disease depends only on how long it has had the disease, and the recovered individuals are permanently immune from further attack. Let $F(t)$ be the probability of an infected individual staying infected for a length of time $ \geqq t$; $f(t)$ be the proportion of initial infectives who are still infective at time t and $I(0)$, $S(0)$ be the proportion of infectives and susceptibles respectively at time zero. We examine the effects of perturbation of the initial condition f on the deterministic model which is given by a system of integral equations and show that the solution of our system of equations is stable at f if and only if the $L^1 $-norm of f is not zero. We also prove that, under appropriate conditions, there exists a positive number $\theta $ depending only on the generalized relative removal rate $\rho = (\alpha \| F \|)^{ - 1} $ such that whe...

A spatial epidemic process where the individuals are located at positions in the Euclidean space R 2 is considered. The infective individuals, with an infection period that is exponentially distributed with parameter µ, move in R 2 according to a Brownian motion with a diffusion coefficient σ 2. The susceptible individuals may also move. But we shall use the approximation that they remain unchanged in numbers and therefore assume that the averaged ‘density' of susceptibles per unit area is the same throughout space and time. The transition probability rate of infection of a susceptible in the infinitesimal element of area dy by an infective in dx is assumed to be a function h(x – y |) of the distance | x – y | between x and y. Then our process can be considered as a two-dimensional birth and death Brownian motion. Let be the number of infective individuals in the set D at time t and . The almost everywhere convergence of the random variables to a limit random variable W(D) is established.

We consider the asymptotic behavior of the solution of a system of nonlinear Volterra integral equations which arises in study of the spread of a disease for which it is assumed that the rate of a susceptible becoming infected depends only on the proportion of infectives, the rate of an infected individual recovering from the disease depends only on the length of time since the disease was contracted, and that recovered individuals are permanently immune from further attack.We examine the limiting behavior of the solution which gives us results on the total size of the epidemic, i.e., the proportion of the total number of individuals that finally contracts the disease.

The bidentate phosphine 2,11-bis(diphenylphosphinomethyl)benzo [c]phenanthrene (1) has been used to prepare the mononuclear, square planar complexes trans-[MX(CO)(1)] and trans-[M(CO)(CH3CN)(1)][BF4] (M = Rh, Ir; X = Cl, Br, I, NCS). It is found that the tendency of these complexes to form adducts with CO, O2 and SO2 is significantly lower than that of the corresponding Ph3P complexes. The oxidative-addition reactions of complexes trans-[IrX (CO) (1)] with hydrogen halides give the six-coordinate species [IrHX2(CO) (1)]. The complexes [IrH2I (CO) (1)] and [IrH2L (CO) (1)] [BF4] (L = CO and CH3CN) have been obtained from hydrogen and the corresponding substrates. The model compounds trans-[MCl (CO) (Ph2PCH2Ph)2] (M = Rh, Ir), trans-[Ir (CO) (CH3CN) (Ph2PCH2Ph)2] [BF4], [IrHCl2(CO)(Ph2PCH2Ph)2] and [IrH2(CO)2(Ph2PCH2Ph)2] [BF4] have been prepared and their special parameters are compared with those of the corresponding complexes of ligand 1. The influence of the static requirements of this ligand on the chemistry of its rhodium and iridium complexes is discussed.

Records of the seasonal distribution and reproductive periods of the Bryozoa are sparse. Much of the available information is based on the finding of ovicelled specimens in dated collections; however, better information is to be had from the few test panel studies which include reports on the more common bryozoans of marine fouling communities. The latter method also permits analysis of larval settling rates and factors involved in the selection of attachment sites. Comprehensive reviews on the test panel studies have been presented by McDougall (1943) and the Woods Hole Oceanographic Institution (1952). Several factors have been found important in connection with bryozoan settling in seasonal studies. Visscher (1927) has demonstrated the importance of dark surfaces for collecting panels, Pomerat and Weiss (1946) have pointed out the effects of surface texture, while Pomerat and Reiner (1942) and McDougall (1943) have shown the influence of substrate angle and light on the attachment of sedentary organisms. The present paper deals with test surface studies on the Bryozoa specifically, utilizing a combination of the techniques of the above workers. It is the purpose of this study to report on the seasonal distribution, spatial distribution, reproductive periods and settling rates of estuarine bryozoans at Beaufort, North Carolina, with a consideration of environmental factors related to these. Other ecological observations on these species have been presented earlier (Maturo 1957). The writer wishes to express his sincere appreciation to Dr. I. E. Gray, under whose guidance this work was done. Thanks are also due to Dr. C. G. Bookhout for placing the many facilities of the Duke University Marine Laboratory at the writer's disposal, and to the U. S. Coast Guard and U. S. Army Corps of Engineers for permission to use permanent pile markers at investigation sites.

The bidentate phosphine 2,11-bis(diphenylphosphinomethyl)benzo [c]phenanthrene (1) has been used to prepare the mononuclear, square planar complexes trans-[MX(CO)(1)] and trans-[M(CO)(CH3CN)(1)][BF4] (M = Rh, Ir; X = Cl, Br, I, NCS). It is found that the tendency of these complexes to form adducts with CO, O2 and SO2 is significantly lower than that of the corresponding Ph3P complexes. The oxidative-addition reactions of complexes trans-[IrX (CO) (1)] with hydrogen halides give the six-coordinate species [IrHX2(CO) (1)]. The complexes [IrH2I (CO) (1)] and [IrH2L (CO) (1)] [BF4] (L = CO and CH3CN) have been obtained from hydrogen and the corresponding substrates. The model compounds trans-[MCl (CO) (Ph2PCH2Ph)2] (M = Rh, Ir), trans-[Ir (CO) (CH3CN) (Ph2PCH2Ph)2] [BF4], [IrHCl2(CO)(Ph2PCH2Ph)2] and [IrH2(CO)2(Ph2PCH2Ph)2] [BF4] have been prepared and their special parameters are compared with those of the corresponding complexes of ligand 1. The influence of the static requirements of this ligand on the chemistry of its rhodium and iridium complexes is discussed.

Let Y(t) be a continuous time pure jump process with state space S = {1,2,...,n} and let ξ0,ξ1,..., be the succession of states visited by Y(t), Δ0,Δ1,... the sojourn times in each state, N(t) the number of transitions before t and \(\Delta _t = t - \sum\limits_{k = 0}^{N(t) - 1} {\Delta _k }\). For each k e S, let Tk(t) be an operator semigroup on a Banach space L with infinitesimal generator ak. Define Tλ (t,ω)=\(T_{\xi _0 } (\tfrac{1}{\lambda }\Delta _0 )T_{\xi _1 } (\tfrac{1}{\lambda }\Delta _1 ) \cdot ... \cdot T_{\xi _{{\rm N}(\lambda t)} } (\tfrac{1}{\lambda }\Delta _{\lambda t} )\). It is known (Kurtz) that if Open image in new window exist for all k = 1,2,...,n and \(\sum\limits_{i = 1}^n {\mu _i = 1}\), then under appropriate conditions the closure of a = \(\sum\limits_{i = 1}^n {\mu _i a_i }\)is the infinitesimal operator for a strongly continuous semigroup T(t) defined on L and Tλ(t,ω) converges almost surely to T(t) as λ → ∞. The existence and identification of this limit is of interest even when the closure of a is not a generator. A probabilistic version of this problem is given in the case of Markovian transition semi-group when the corresponding processes have identical hitting distributions. Sufficient conditions for the existence of limit are given. With S = {1,2} and \(\left\{ \begin{gathered}1,2n \leqslant t < 2n + 1 \hfill \\2,2n + 1 \leqslant t < 2n + 2 \hfill \\\end{gathered} \right.\), n = 0,1,2,..., the result is obtained by Loren Pitt.