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PubMed2001

Chameleons have independent eye movements but synchronise both eyes during saccadic prey tracking.

The movements of both eyes and the head were recorded with search coils in unrestrained, freely moving chameleons. As a main result I found that the generation of saccades in the left and the right eye was either independent from each other or was highly correlated according to the behavioural situation. When no prey item was fixated, disconjugate saccades were observed which was in accordance with earlier observations in chameleons. During prey tracking the chameleons switched to a different oculomotor behaviour and pursued the moving prey with synchronous saccades. At higher target velocities, the tracking movement of the head was also saccadic and was synchronised with the two eyes. Binocular coupling affected only the timing of the saccades but not the metrics: the amplitudes of the synchronous saccades were usually different in the two eyes. These observations suggest the existence of two independent premotor neuronal circuits for left and right eye saccadic motor control in the chameleon. Binocular coupling in prey-tracking chameleons is probably achieved by neuronal coupling of these premotor circuits during eye-head coordination. The ability to switch between synchronous and uncoupled saccadic eye movements has not been described for any other vertebrate. This unique ability of the chameleon may help to understand the organisation of the oculomotor system of other vertebrates since evidence for separate left eye and right eye saccade generation and position control has recently also been reported in primates.

Animals↗

PubMed2002

Indirect effects of heavy metals on parasites may cause shifts in snail species compositions.

We studied the direct and indirect effects of pollution on the distributions and abundances of two closely related species of pulmonate freshwater snails. Physella columbiana is more numerous at heavy metal-polluted lakes, and Lymnaea palustris is more numerous at reference lakes. Both species are present at all sites, as are predatory bluegill sunfish (Lepomis macrochirus). The direct effects examined included the snails' growth and reproduction in both the presence and absence of heavy metals and their short-term survival when exposed to large concentrations of heavy metals. The indirect effects were the species' ability to elude capture by sunfish and the diversity and abundance of parasites within the snails. We found that heavy metals had little direct effect on growth and reproduction and that both species acquired similar levels of metals in their tissues. Interestingly, P. columbiana (the more abundant species in polluted lakes) actually exhibited higher recruitment in the absence of metals than did L. palustris (reference lakes). L. palustris has life history characteristics that favor increased growth and reduced reproduction. These characteristics resulted in decreased predation of adults by gape-limited predators and a greater ability to cope with heavy parasite burdens. P. columbiana exhibited slower growth, which resulted in increased predation although higher reproduction rates may compensate.The major effect of heavy metals on species distributions was indirect on the snails' parasites. Parasites appeared to be very susceptible to metals, and this resulted in lower parasite diversity and intensities at polluted sites for both species of snails. P. columbiana may only be able to outcompete L. palustris at polluted sites due to the indirect effects of heavy metals; the negative effect of heavy metals on parasites, and a proposed negative effect of metals on the foraging ability of sunfish that favors the faster-reproducing P. columbiana.

Animals↗

PubMed2003

Environmental contaminants in liver and kidney of free-ranging northern goshawks (Accipiter gentilis) from three regions of Germany.

The northern goshawk (Accipiter gentilis) is a top predator in the terrestrial food web of large parts of the Holarctic. Due to its sedentary nature and well-investigated feeding ecology, it represents the most suitable bird of prey species in continental Europe for monitoring environmental pollutants. We analyzed the levels of organochlorine pesticides, polychlorinated biphenyls (PCB), and nonessential heavy metals in organ samples of 62 free-ranging northern goshawks found dead or injured in Germany from 1995 to 2001. Our results indicate significant differences in the contaminant burden of northern goshawks between three regions in Germany. Presumably, these differences were caused by different application periods and legislative restrictions before the German reunion, especially for the use of DDT in agriculture and forestry. Extraordinarily high residues of PCBs and DDE, the main metabolite of DDT, were found mainly in livers of northern goshawks inhabiting Berlin. Body condition is highly negatively correlated with the contamination level of the individual, especially for the persistent and lipophilic organochlorines and for mercury. PCB concentrations in hepatic tissue increase rapidly with age, and birds in their first summer had significantly lower levels than birds in their first winter or older. Adult female northern goshawks from Berlin had significantly higher hepatic concentrations of most of the higher-chlorinated PCBs and of cadmium than males from the same region. Cadmium residues were in general higher in renal tissue than in hepatic tissue, and cadmium levels in kidneys increased with age. Lead concentrations indicative of acute lead poisoning were detected in one bird and suggested in two others. All other heavy metal concentrations were low and represent background levels for birds of prey in Germany.

Animals↗

PubMed2005

Trends of chlorinated organic contaminants in great lakes trout and walleye from 1970 to 1998.

Levels of chlorinated organic contaminants in predator fish have been monitored annually in each of the Great Lakes since the 1970s. This article updates earlier reports with data from 1991 to 1998 for lake trout (Salvelinus namaycush) and (Lake Erie only) walleye (Sander vitreus) to provide a record that now extends nearly 30 years. Whole fish were analyzed for a number of industrial contaminants and pesticides, including polychlorinated biphenyls (PCBs), dichloro-diphenyl-trichloroethane (DDT), dieldrin, toxaphene, and mirex, and contaminant trends were quantified using multicompartment models. As in the past, fish from Lakes Michigan, Ontario, and Huron have the highest levels of PCBs, DDT, and dieldrin; Superior has the highest levels of toxaphene; and Ontario has the highest levels of mirex. In the period after curtailment of chemical use, concentrations rapidly decreased, represented by relatively short half-lives from approximately 1 to 9 years. Although trends depend on both the contaminant and the lake, in many cases the rate of decline has been decreasing, and concentrations are gradually approaching an irreducible concentration. For dioxin-like PCBs, levels have not been decreasing during the most recent 5-year period (1994 to 1998). In some cases, the year-to-year variation in contaminant levels is large, mainly because of food-web dynamics. Although this variation sometimes obscures long-term trends, the general pattern of a rapid decrease followed by slowing or leveling-off of the downward trend seems consistent across the Great Lakes, and future improvements of the magnitude seen in the 1970s and early 1980s likely will take much longer.

Animals↗

PubMed2003

Effects of temperature and turbulence on the predator-prey interactions between a heterotrophic flagellate and a marine bacterium.

Biotic and abiotic factors can influence interactions between microbial grazers and their prey, thus impacting both the cycling of biogenic carbon within the surface layer of the ocean and the export of carbon to the deep ocean and higher trophic levels. In this study, microcosm experiments were used to evaluate the combined effect of temperature and turbulence on the growth rate of a marine bacterium (Vibrio splendidus), a protistan predator (Paraphysomonas sp.), and the community grazing impact of Paraphysomonas sp. on V. splendidus. It was found that the artificial turbulence generated (1.35 x 10-1 cm2 s-3) significantly increased the rates of growth of Paraphysomonas sp. at high (>10 degrees C), but not low (<5 degrees C) temperatures, and that turbulence had no effect on the growth of V. splendidus. Both flagellate and bacterial growth were temperature dependent and decreased 4- to 6-fold as temperatures decreased from 15 to 0 degrees C. Bacterial grazing mortality by Paraphysomonas sp. was 1.3- to 2.5-fold greater in the turbulent than static treatments among all four temperatures, and the rates of cell-specific ingestion of bacteria by Paraphysomonas sp. was 2-fold greater at 15 and 10 degrees C in the turbulent than in the static treatment. Hence, this study shows that turbulence can influence nanoflagellate grazing at temperatures >5 degrees C and suggests that at low temperatures, increased viscosity may limit the size of organisms that can be affected by small-scale turbulence.

Animals↗

PubMed2005

Effects of viruses and predators on prokaryotic community composition.

Dialysis bags were used to examine the impact of predation and viral lysis on prokaryotic community composition (PCC) over a 5-day experiment in the oligomesotrophic Lake Pavin (France). The impact of the different predator communities (protists and metazoans) of prokaryotes was estimated by water fractionation (<5 microm: treatment filtered on 5 microm, without ciliates and metazoans; UNF: unfiltered treatment with all planktonic communities). Enrichments of natural viruses (<1.2 microm: with a natural virus concentration; <1.2 mum V and VV: with enrichment leading to a double or triple concentration of viruses, respectively) were used to indirectly assess the control of virioplankton. Viral activity was estimated from the frequency of visibly infected cells (FVIC). PCC was determined by fluorescence in situ hybridization (FISH) and terminal restriction fragment length polymorphism (T-RFLP). In this study, PCC was affected by the eukaryote communities (especially flagellates), and viruses to a lesser extent. Cyanobacteria declined significantly during the experiment and were highly correlated with the FVIC. In addition, the 503-bp terminal restriction fragment (T-RF) disappeared in treatments with virus enrichments, suggesting possible viral-associated mortality processes, whereas the 506-bp T-RF was not affected in these treatments. On one hand, these results suggest a control of the PCC: first, by viral lysis of some dominant phylotypes and second, by interspecific competition between resistant strains for the uptake of substrates released by this lysis. The increase of Archaea may suggest that these cells benefit such resources. On the other hand, the disappearance and the stable proportion of some dominant phylotypes suggested a selection pressure due to the predatory activity on prokaryotes. In conclusion, prokaryotic abundance appears to be mainly controlled by flagellate protists, which also affected PCC, whereas viruses seemed to be essentially responsible for profound changes in PCC via direct and indirect actions.

Animals↗

PubMed2006

Feeding characteristics of an amoeba (Lobosea: Naegleria) grazing upon cyanobacteria: food selection, ingestion and digestion progress.

Bacterivory by heterotrophic nanoflagellates and ciliates has been widely studied in aquatic environments, but data on the grazing of amoebae, are still scarce. From the water samples of Dianchi Lake (Kunming, Yunnan Province, China), we isolated an amoeba, designated as Naegleria sp. strain W2, which had potent grazing effects on some kind of cyanobacteria. The food selection mechanism and the digestion process of the amoeba were investigated in batch experiments. Predation experiments showed that filamentous cyanobacteria (e.g., Anabaena, Cylindrospermum, Gloeotrichia, and Phormidium) were readily consumed, with clearance rates ranging from 0.332 to 0.513 nL amoeba(-1) h(-1). The tight threads (Oscilltoria) and aggregates (Aphanizomenon) could not be ingested; however, their sonicated fragments were observed inside food vacuoles, suggesting that their morphologies prevent them from being ingested. Live video microscopy noted that unicellular Chroococcaceae (e.g., Synechococcus, Aphanocapsa, and Microcystis) were excreted after ingestion, indicating that food selection takes place inside food vacuoles. To determine whether the tastes or the toxins prevented them from being digested, heat-killed cells were retested for predation. Digestion rates and ingestion rates of the amoebae for filamentous cyanobacteria were estimated from food vacuole content volume. Through a "cold-chase" method, we found that the food vacuole contents declined exponentially in diluted amoebae cells, and digestion rates were relatively constant, averaging about 1.5% food vacuole content min(-1) at 28 degrees Celsius. Ingestion strongly depended on the satiation status of the amoebae, starved amoebae fed at higher rates compared with satiated amoebae. Our results suggest that the food selection and food processing mechanisms of the amoeba are similar to those of interception feeding flagellates; however, filamentous cyanobacteria cannot obtain a refuge under the grazing pressure of phagotrophic amoebae, which may widen our knowledge on the grazing of protists.

Amoeba↗

PubMed2002

Evaluation of immunocontraception as a publicly acceptable form of vertebrate pest species control: the introduced grey squirrel in Britain as an example.

We sent out a targeted questionnaire to organizations and private individuals across the UK that have expressed an interest in squirrel management and conservation. Respondents were asked to evaluate shooting, trapping, poisoning and immunocontraception (IMC), according to their perceived efficacy, cost efficiency, and whether they were considered to be humane. The majority of both professionals and enthusiasts indicated support for grey squirrel control to help conserve red squirrels and to reduce economic damage to timber crops. Respondents\' comparative evaluations of current forms of control showed that trapping is the most acceptable method. When IMC is compared with the other methods, it was considered to be more humane and acceptable. In contrast, poisoning was seen as humane or acceptable by the fewest respondents. Furthermore, poisoning elicited the greatest difference in opinion between the professional and enthusiast groups. This difference (34\%) may be interpreted partly as concern over the type of death that results from poisoning and partly as due to the possibility of poisoning nontarget species. Our findings indicate a need for more public information regarding secondary poisoning hazards to other species and their predators. Interest and concern about squirrel control correlated with the overlap between contemporary areas of distribution of the two species. It is these areas where consultation and education programs about control methods should be targeted. This research indicates that there would be support for grey squirrel control using IMC from both lay and professional interest groups. It demonstrates the existence of a sound basis for constructive dialog that can lead to the design and implementation of acceptable and efficient control strategies.

Animals↗

PubMed2003

Living amidst large wildlife: livestock and crop depredation by large mammals in the interior villages of Bhadra Tiger Reserve, South India.

Conflict with humans over livestock and crops seriously undermines the conservation prospects of India's large and potentially dangerous mammals such as the tiger (Panthera tigris) and elephant (Elephas maximus). This study, carried out in Bhadra Tiger Reserve in south India, estimates the extent of material and monetary loss incurred by resident villagers between 1996 and 1999 in conflicts with large felines and elephants, describes the spatiotemporal patterns of animal damage, and evaluates the success of compensation schemes that have formed the mainstay of loss-alleviation measures. Annually each household lost an estimated 12% (0.9 head) of their total holding to large felines, and approximately 11% of their annual grain production (0.82 tonnes per family) to elephants. Compensations awarded offset only 5% of the livestock loss and 14% of crop losses and were accompanied by protracted delays in the processing of claims. Although the compensation scheme has largely failed to achieve its objective of alleviating loss, its implementation requires urgent improvement if reprisal against large wild mammals is to be minimized. Furthermore, innovative schemes of livestock and crop insurance need to be tested as alternatives to compensations.

Agriculture↗

PubMed2001

A landscape analysis of cougar distribution and abundance in Montana, USA.

Recent growth in the distribution and abundance of cougars (Puma concolor) throughout western North America has created opportunities, challenges, and problems for wildlife managers and raises questions about what factors affect cougar populations. We present an analysis of factors thought to affect cougar distribution and abundance across the broad geographical scales on which most population management decisions are made. Our objectives were to: (1) identify and evaluate landscape parameters that can be used to predict the capability of habitats to support cougars, and (2) evaluate factors that may account for the recent expansion in cougar numbers. Habitat values based on terrain ruggedness and forested cover explained 73% of the variation in a cougar abundance index. Indices of cougar abundance also were spatially and temporally correlated with ungulate abundance. An increase in the number and total biomass of ungulate prey species is hypothesized to account for recent increases in cougars. Cougar populations in Montana are coping with land development by humans when other components of habitat and prey populations are sufficient. Our analysis provides a better understanding of what may have influenced recent growth in cougar distribution and abundance in Montana and, when combined with insights about stakeholder acceptance capacity, offers a basis for cougar management at broad scales. Long-term conservation of cougars necessitates a better understanding of ecosystem functions that affect prey distribution and abundance, more accurate estimates of cougar populations, and management abilities to integrate these components with human values.

Animal Husbandry↗

PubMed2003

Existence of traveling wave solutions in a diffusive predator-prey model.

We establish the existence of traveling front solutions and small amplitude traveling wave train solutions for a reaction-diffusion system based on a predator-prey model with Holling type-II functional response. The traveling front solutions are equivalent to heteroclinic orbits in R(4) and the small amplitude traveling wave train solutions are equivalent to small amplitude periodic orbits in R(4). The methods used to prove the results are the shooting argument and the Hopf bifurcation theorem.

Animals↗

PubMed2003

Deriving reaction-diffusion models in ecology from interacting particle systems.

We use a scaling procedure based on averaging Poisson distributed random variables to derive population level models from local models of interactions between individuals. The procedure is suggested by using the idea of hydrodynamic limits to derive reaction-diffusion models for population interactions from interacting particle systems. The scaling procedure is formal in the sense that we do not address the issue of proving that it converges; instead we focus on methods for computing the results of the scaling or deriving properties of rescaled systems. To that end we treat the scaling procedure as a transform, in analogy with the Laplace or Fourier transform, and derive operational formulas to aid in the computation of rescaled systems or the derivation of their properties. Since the limiting procedure is adapted from work by Durrett and Levin, we refer to the transform as the Durrett-Levin transform. We examine the effects of rescaling in various standard models, including Lotka-Volterra models, Holling type predator-prey models, and ratio-dependent models. The effects of scaling are mostly quantitative in models with smooth interaction terms, but ratio-dependent models are profoundly affected by the scaling. The scaling transforms ratio-dependent terms that are singular at the origin into smooth terms. Removing the singularity at the origin eliminates some of the unique dynamics that can arise in ratio-dependent models.

Animals↗

PubMed2004

Consequences of symbiosis for food web dynamics.

Basic Lotka-Volterra type models in which mutualism (a type of symbiosis where the two populations benefit both) is taken into account, may give unbounded solutions. We exclude such behaviour using explicit mass balances and study the consequences of symbiosis for the long-term dynamic behaviour of a three species system, two prey and one predator species in the chemostat. We compose a theoretical food web where a predator feeds on two prey species that have a symbiotic relationships. In addition to a species-specific resource, the two prey populations consume the products of the partner population as well. In turn, a common predator forages on these prey populations. The temporal change in the biomass and the nutrient densities in the reactor is described by ordinary differential equations (ODE). Since products are recycled, the dynamics of these abiotic materials must be taken into account as well, and they are described by odes in a similar way as the abiotic nutrients. We use numerical bifurcation analysis to assess the long-term dynamic behaviour for varying degrees of symbiosis. Attractors can be equilibria, limit cycles and chaotic attractors depending on the control parameters of the chemostat reactor. These control parameters that can be experimentally manipulated are the nutrient density of the inflow medium and the dilution rate. Bifurcation diagrams for the three species web with a facultative symbiotic association between the two prey populations, are similar to that of a bi-trophic food chain; nutrient enrichment leads to oscillatory behaviour. Predation combined with obligatory symbiotic prey-interactions has a stabilizing effect, that is, there is stable coexistence in a larger part of the parameter space than for a bi-trophic food chain. However, combined with a large growth rate of the predator, the food web can persist only in a relatively small region of the parameter space. Then, two zero-pair bifurcation points are the organizing centers. In each of these points, in addition to a tangent, transcritical and Hopf bifurcation a global heteroclinic bifurcation is emanating. This heteroclinic cycle connects two saddle equilibria where the predator is absent. Under parameter variation the period of the stable limit cycle goes to infinity and the cycle tends to the heteroclinic cycle. At this global bifurcation point this cycle breaks and the boundary of the basin of attraction disappears abruptly because the separatrix disappears together with the cycle. As a result, it becomes possible that a stable two-nutrient-two-prey population system becomes unstable by invasion of a predator and eventually the predator goes extinct together with the two prey populations, that is, the complete food web is destroyed. This is a form of over-exploitation by the predator population of the two symbiotic prey populations. When obligatory symbiotic prey-interactions are modelled with Liebig's minimum law, where growth is limited by the most limiting resource, more complicated types of bifurcations are found. This results from the fact that the Jacobian matrix changes discontinuously with respect to a varying parameter when another resource becomes most limiting.

Algorithms↗

PubMed2004

A stage structured predator-prey model and its dependence on maturation delay and death rate.

Many of the existing models on stage structured populations are single species models or models which assume a constant resource supply. In reality, growth is a combined result of birth and death processes, both of which are closely linked to the resource supply which is dynamic in nature. From this basic standpoint, we formulate a general and robust predator-prey model with stage structure with constant maturation time delay (through-stage time delay) and perform a systematic mathematical and computational study. Our work indicates that if the juvenile death rate (through-stage death rate) is nonzero, then for small and large values of maturation time delays, the population dynamics takes the simple form of a globally attractive steady state. Our linear stability work shows that if the resource is dynamic, as in nature, there is a window in maturation time delay parameter that generates sustainable oscillatory dynamics.

Animals↗

PubMed2004

Heteroclinic bifurcation in a ratio-dependent predator-prey system.

In this paper we study the heteroclinic bifurcation in a general ratio-dependent predator-prey system. Based on the results of heteroclinic loop obtained in [J. Math. Biol. 43(2001): 221-246], we give parametric conditions of the existence of the heteroclinic loop analytically and describe the heteroclinic bifurcation surface in the parameter space, so as to answer further the open problem raised in [J. Math. Biol. 42(2001): 489-506].

Animals↗

PubMed2005

Modelling of predator-prey trophic interactions. Part I: two trophic levels.

A class of lumped parameter models to describe the local dynamics in a controlled environment of a two-trophic chain is considered. The class is characterized by a trophic function (functional response of predator to the abundance of prey) depending on the ratio of prey biomass x and a linear function of predator biomass y: f(qx/[(1-rho)k + rhoy]), where q is the efficiency of the predation process, k is a reference biomass, and rho (0 < or = rho < or = 1) specifies the predation model. The trophic function is defined only by some properties determining its shape. A stability analysis of the models has been performed by taking the parameters q and rho as bifurcation parameters: the regions in the (rho,q) plane of existence and stability of nonnegative equilibrium states and limit cycles are determined. This analysis shows that the behaviour of the models is qualitatively similar for 0 < or = rho < 1 (in particular the null state is always a saddle point), while the value rho=1 gives rise to some kind of structural instability of the system (in particular the null state becomes an attractor for sufficiently high predation efficiency).

Animals↗

PubMed2006

Prediction of predator-prey populations modelled by perturbed ODEs.

In this paper we explore a stochastic model in continuous time for predator-prey interactions, which accounts for the periodical behaviour observed in many animal populations. More precisely, we consider a solution to the classical Lotka-Volterra system of equations, but we view the actual population sizes as random perturbations of the solutions to this ODE system. Namely, we assume that the perturbations follow correlated Ornstein-Uhlenbeck processes; this approach generalizes the one of Froda and Colavita [Aust N Z J Stat 2:235-254, 2005] who considered only i.i.d. errors. This type of perturbed deterministic model allows to perform parameter estimation and to predict population sizes at future times. On the other hand, the present model refines the previous one since it takes into account the variability due to external factors and the time dependence in the random component. Moreover, this more flexible model improves the predictions of population sizes at future times. In order to illustrate this last point, we analyse two data sets.

Animals↗

PubMed2006

Modelling of predator-prey trophic interactions. Part II: three trophic levels.

A general class of lumped parameter models describing the local dynamics of a tri-trophic chain in a controlled environment is analyzed in detail. The trophic functions characterizing the interactions are defined only by some properties and allow us to treat both prey-dependent and ratio-dependent models in a unified manner. Conditions for existence and stability of extinction and coexistence equilibrium states are determined. Some peculiar aspects of the dynamics of the system depending on the bioecological parameters are presented, with particular attention to bistability situations, limit cycles and chaotic behaviours.

Animals↗