An experimental study of declining populations

2005 ◽  
Vol 32 (6) ◽  
pp. 481 ◽  
Author(s):  
Jim Hone ◽  
the late Graeme Caughley ◽  
David Grice
Keyword(s):  
Experimental Study ◽  
Population Decline ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Second Phase ◽  
Population Declines ◽  
Negative Effects ◽  
Instantaneous Rate ◽  
Rate Of Increase ◽  
Declining Populations

Wildlife population declines have been attributed to predation, habitat change, and other agents of decline. An experimental study applied predation (at three levels) and habitat (at two levels) treatments over two years and measured the patterns of decline of populations of a medium-sized mammal (European rabbits). A model of population dynamics and effects of the treatments predicted negative effects of both treatments and an interaction of the treatments. All populations declined during the study including the experimental controls. During the first seven months (first phase of the study) the rate of decline, as estimated by the observed monthly instantaneous rate of increase (r), was more negative (P < 0.05) with increasing predation levels but there was no effect (P > 0.05) of habitat manipulation on r. There were no significant effects of treatments on rabbit abundance, or density, during the first phase of the study. During the second phase of the study, of 12 months’ duration, there were no significant (P > 0.05) effects of treatments on rabbit abundance, density, or r. There were no significant (P > 0.05) interactions of treatments on any response variable during either phase of the study. The interaction predicted by the theoretical model was not supported. Estimated abundance at the end of the study was not related (P > 0.05) to initial abundance (correlation = 0.023). The implications of the results are that such experimental studies can be used to evaluate theoretical models, though such studies may require a larger number of treatment replicates, and treatments at more extreme levels, to more clearly detect the effects of agents of population decline and their interactions.

scholarly journals Size-specific Advantage in Shelter Competition between the Mountain Madtom and Crayfishes

2020 ◽  
pp. 0000-0000
Author(s):  
Meredith H Harris ◽  
Kristin I Womble ◽  
J Brian Alford
Keyword(s):  
Population Decline ◽  
Relative Size ◽  
Limited Resource ◽  
Fish Population ◽  
Health Condition ◽  
Population Declines ◽  
Negative Effects ◽  
Growth And Survival ◽  
Crucial Component ◽  
Behavioral Trials

Shelter is a crucial component to many species' survival, and when shelter becomes limited, resulting competition can have negative effects on growth and survival. In Little Chucky Creek, a tributary to the Nolichucky River in Tennessee, the severe population decline of the Chucky Madtom Noturus crypticus has been partially attributed to an increase in the abundance of cavity-dwelling crayfish following the establishment of two nonnative species. While it has been suggested that the crayfish exclude the cavity-dwelling fish from shelter, we are not aware of studies that have been conducted to demonstrate that crayfish directly outcompete madtoms in this regard. Our objective was to experimentally test the hypothesis that shelter competition between crayfish and the Mountain Madtom N. eleutherus, a surrogate species for the Chucky Madtom, is a function of relative size. Behavioral trials were conducted in which shelter was the limited resource for the two potential competitors. The madtoms' success at occupying the provided cover object was recorded for 5 days as well as health condition at the end of the competition phase. Both madtom occupancy and health condition were positively correlated with increasing relative size. As the size differential increased between madtoms and crayfish, madtoms were more successful at occupying the cover object, and overall condition was greater at the end of the trial. Conversely, when madtoms were smaller than crayfish, individuals were more commonly excluded from the cover object or even killed. Juvenile madtoms experienced 100% mortality. We concluded that crayfish exhibit a size-specific competitive advantage over Mountain Madtoms when shelter is limited, and that crayfishes may catalyze fish population declines at least partially through shelter exclusion and predation on juveniles.

scholarly journals The role of predation in the decline and extirpation of woodland caribou

2020 ◽  
Author(s):  
Heiko Wittmer ◽  
ARE Sinclair ◽  
BN McLellan
Keyword(s):  
Rangifer Tarandus ◽  
Population Decline ◽  
Temporal Distribution ◽  
Pregnancy Rates ◽  
Foraging Habitat ◽  
Woodland Caribou ◽  
Instantaneous Rate ◽  
Population Growth Rates ◽  
Rate Of Increase ◽  
Winter Foraging

To select appropriate recovery strategies for endangered populations, we must understand the dynamics of small populations and distinguish between the possible causes that drive such populations to low numbers. It has been suggested that the pattern of population decline may be inversely density-dependent with population growth rates decreasing as populations become very small; however, empirical evidence of such accelerated declines at low densities is rare. Here we analyzed the pattern of decline of a threatened population of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada. Using information on the instantaneous rate of increase relative to caribou density in suitable winter foraging habitat, as well as on pregnancy rates and on causes and temporal distribution of mortalities from a sample of 349 radiocollared animals from 15 subpopulations, we tested 3 hypothesized causes of decline: (a) food regulation caused by loss of suitable winter foraging habitat, (b) predation-sensitive foraging caused by loss of suitable winter foraging habitat and (c) predation with caribou being secondary prey. Population sizes of caribou subpopulations ranged from <5 to >500 individuals. Our results showed that the rates of increase of these subpopulations varied from -0.1871 to 0.0496 with smaller subpopulations declining faster than larger subpopulations. Rates of increase were positively related to the density of caribou in suitable winter foraging habitat. Pregnancy rates averaged 92.4% ±2.24 and did not differ among subpopulations. In addition, we found predation to be the primary cause of mortality in 11 of 13 subpopulations with known causes of mortality and predation predominantly occurred during summer. These results are consistent with predictions that caribou subpopulations are declining as a consequence of increased predation. Recovery of these woodland caribou will thus require a multispecies perspective and an appreciation for the influence of inverse density dependence on population trajectories. © Springer-Verlag 2005.

scholarly journals Examining the Evidence for Regulated and Programmed Cell Death in Cyanobacteria. How Significant Are Different Forms of Cell Death in Cyanobacteria Population Dynamics?

2021 ◽  
Vol 12 ◽  
Author(s):  
Daniel J. Franklin
Keyword(s):  
Cell Death ◽  
Population Dynamics ◽  
Population Decline ◽  
Natural Populations ◽  
Biotic Interactions ◽  
Theoretical Models ◽  
Freshwater Ecosystems ◽  
Anthropogenic Factors ◽  
Population Fluctuations ◽  
Population Declines

Cyanobacteria are ancient and versatile members of almost all aquatic food webs. In freshwater ecosystems some cyanobacteria form “bloom” populations containing potent toxins and such blooms are therefore a key focus of study. Bloom populations can be ephemeral, with rapid population declines possible, though the factors causing such declines are generally poorly understood. Cell death could be a significant factor linked to population decline. Broadly, three forms of cell death are currently recognized – accidental, regulated and programmed – and efforts are underway to identify these and standardize the use of cell death terminology, guided by work on better-studied cells. For cyanobacteria, the study of such differing forms of cell death has received little attention, and classifying cell death across the group, and within complex natural populations, is therefore hard and experimentally difficult. The population dynamics of photosynthetic microbes have, in the past, been principally explained through reference to abiotic (“bottom-up”) factors. However, it has become clearer that in general, only a partial linkage exists between abiotic conditions and cyanobacteria population fluctuations in many situations. Instead, a range of biotic interactions both within and between cyanobacteria, and their competitors, pathogens and consumers, can be seen as the major drivers of the observed population fluctuations. Whilst some evolutionary processes may theoretically account for the existence of an intrinsic form of cell death in cyanobacteria, a range of biotic interactions are also likely to frequently cause the ecological incidence of cell death. New theoretical models and single-cell techniques are being developed to illuminate this area. The importance of such work is underlined by both (a) predictions of increasing cyanobacteria dominance due to anthropogenic factors and (b) the realization that influential ecosystem modeling work includes mortality terms with scant foundation, even though such terms can have a very large impact on model predictions. These ideas are explored and a prioritization of research needs is proposed.

scholarly journals Effects of spirodiclofen on the reproductive potential of two-spotted spider mite (Acari: Tetranychidae) ovipositing females

2009 ◽  
Vol 61 (4) ◽  
pp. 777-785 ◽  
Author(s):  
D. Marcic ◽  
Irena Ogurlic ◽  
P. Peric
Keyword(s):  
Spider Mite ◽  
Population Decline ◽  
Survival Rates ◽  
Reproductive Potential ◽  
Adult Emergence ◽  
Egg Laying ◽  
Instantaneous Rate ◽  
Rate Of Increase ◽  
Survival And Reproduction ◽  
Two Spotted Spider Mite

A laboratory bioassay was conducted to evaluate the effects of spirodiclofen on the survival and reproduction of young and mated females of two-spotted spider mite (Tetranychus urticae Koch). The females were sprayed with a series of acaricide concentrations (96, 48, 24, 12, and 6 mg/l) 24-30 h after adult emergence, i.e., at the age most likely to exhibit dispersal behavior and close to their reproductive maximum. The proportions of T. urticae females that survived treatment without symptoms of poisoning were concentration-dependent, ranging between 0.41 and 0.88 (0.96 in the control). With the exception of females that survived 6 mg/l, fecundity of the treated female mites was strongly affected during the exposure, compared to the control. The mean daily fecundity (EL) and mean daily fertility (EH) of surviving females, transferred daily to new leaf disks over the following five days, significantly decreased as spirodiclofen concentrations increased. In treatments with 6 mg/l and 12 mg/l, only the latter concentration significantly reduced both EL and EH, compared to the control. In females that survived 24 mg/l and 48 mg/l, these life history parameters were reduced by over 90%, while treatment with 96 mg/l completely terminated egg-laying. The treated females lived for a significantly shorter time than untreated ones, with the exception of females that survived 6 mg/l. Compared to the control females, gross fecundity (GL) and gross fertility (GH) of the treated females were strongly reduced on the first and second day; from the third day onward, females treated with the lowest concentrations achieved marked recovery, their GL and GH going even above the values in the control. However, net fecundity (NL) and net fertility (NH) of all treated females decreased considerably throughout the trial, indicating that survival rates of these females were lower, compared to the control. Calculated as total sums of gross and net daily schedules within five days, fecundity and fertility significantly decreased as spirodiclofen concentration increased. The two lowest concentrations failed to achieve a significant reduction of GL, while GH, NL, and NH were significantly lower than control values starting with the females treated with 6 mg/L. A high percentage of unhatched eggs, especially during the initial two days after treatment (35-100%), further contributed to the significant reduction in fertility of the females treated with spirodiclofen. All concentrations of spirodiclofen significantly reduced the instantaneous rate of increase. Regression analysis showed a linear population decline with increased acaricide concentrations (y = 1.13 - 0.24x; R2 = 0.91, p < 0.05).

scholarly journals The role of predation in the decline and extirpation of woodland caribou

2020 ◽  
Author(s):  
Heiko Wittmer ◽  
ARE Sinclair ◽  
BN McLellan
Keyword(s):  
Rangifer Tarandus ◽  
Population Decline ◽  
Temporal Distribution ◽  
Pregnancy Rates ◽  
Foraging Habitat ◽  
Woodland Caribou ◽  
Instantaneous Rate ◽  
Population Growth Rates ◽  
Rate Of Increase ◽  
Winter Foraging

To select appropriate recovery strategies for endangered populations, we must understand the dynamics of small populations and distinguish between the possible causes that drive such populations to low numbers. It has been suggested that the pattern of population decline may be inversely density-dependent with population growth rates decreasing as populations become very small; however, empirical evidence of such accelerated declines at low densities is rare. Here we analyzed the pattern of decline of a threatened population of woodland caribou (Rangifer tarandus caribou) in British Columbia, Canada. Using information on the instantaneous rate of increase relative to caribou density in suitable winter foraging habitat, as well as on pregnancy rates and on causes and temporal distribution of mortalities from a sample of 349 radiocollared animals from 15 subpopulations, we tested 3 hypothesized causes of decline: (a) food regulation caused by loss of suitable winter foraging habitat, (b) predation-sensitive foraging caused by loss of suitable winter foraging habitat and (c) predation with caribou being secondary prey. Population sizes of caribou subpopulations ranged from <5 to >500 individuals. Our results showed that the rates of increase of these subpopulations varied from -0.1871 to 0.0496 with smaller subpopulations declining faster than larger subpopulations. Rates of increase were positively related to the density of caribou in suitable winter foraging habitat. Pregnancy rates averaged 92.4% ±2.24 and did not differ among subpopulations. In addition, we found predation to be the primary cause of mortality in 11 of 13 subpopulations with known causes of mortality and predation predominantly occurred during summer. These results are consistent with predictions that caribou subpopulations are declining as a consequence of increased predation. Recovery of these woodland caribou will thus require a multispecies perspective and an appreciation for the influence of inverse density dependence on population trajectories. © Springer-Verlag 2005.

Analytical Electron Microscopy of Surface-Modified Ceramics

1985 ◽  
Vol 43 ◽  
pp. 276-279
Author(s):  
P. S. Sklad
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Theoretical Models ◽  
Ceramic Materials ◽  
Solute Concentration ◽  
Second Phase ◽  
Analytical Electron ◽  
Implantation Techniques ◽  
Lattice Damage ◽  
Surface Modified

Over the past several years, it has become increasingly evident that materials for proposed advanced energy systems will be required to operate at high temperatures and in aggressive environments. These constraints make structural ceramics attractive materials for these systems. However it is well known that the condition of the specimen surface of ceramic materials is often critical in controlling properties such as fracture toughness, oxidation resistance, and wear resistance. Ion implantation techniques offer the potential of overcoming some of the surface related limitations.While the effects of implantation on surface sensitive properties may be measured indpendently, it is important to understand the microstructural evolution leading to these changes. Analytical electron microscopy provides a useful tool for characterizing the microstructures produced in terms of solute concentration profiles, second phase formation, lattice damage, crystallinity of the implanted layer, and annealing behavior. Such analyses allow correlations to be made with theoretical models, property measurements, and results of complimentary techniques.

A Relativistic Newtonian Mechanics Predicts with Precision the Results of Recent Neutrino-Velocity Experiments

2014 ◽  
Vol 6 (1) ◽  
pp. 1032-1035 ◽  
Author(s):  
Ramzi Suleiman
Keyword(s):  
Null Hypothesis ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Newtonian Mechanics ◽  
Speed Of Light ◽  
Symmetry Principle ◽  
Proposed Model ◽  
Significant Difference ◽  
The One ◽  
Complete Collapse

The research on quasi-luminal neutrinos has sparked several experimental studies for testing the "speed of light limit" hypothesis. Until today, the overall evidence favors the "null" hypothesis, stating that there is no significant difference between the observed velocities of light and neutrinos. Despite numerous theoretical models proposed to explain the neutrinos behavior, no attempt has been undertaken to predict the experimentally produced results. This paper presents a simple novel extension of Newton's mechanics to the domain of relativistic velocities. For a typical neutrino-velocity experiment, the proposed model is utilized to derive a general expression for . Comparison of the model's prediction with results of six neutrino-velocity experiments, conducted by five collaborations, reveals that the model predicts all the reported results with striking accuracy. Because in the proposed model, the direction of the neutrino flight matters, the model's impressive success in accounting for all the tested data, indicates a complete collapse of the Lorentz symmetry principle in situation involving quasi-luminal particles, moving in two opposite directions. This conclusion is support by previous findings, showing that an identical Sagnac effect to the one documented for radial motion, occurs also in linear motion.

scholarly journals The effects of modern war and military activities on biodiversity and the environment

2015 ◽  
Vol 23 (4) ◽  
pp. 443-460 ◽  
Author(s):  
Michael J. Lawrence ◽  
Holly L.J. Stemberger ◽  
Aaron J. Zolderdo ◽  
Daniel P. Struthers ◽  
Steven J. Cooke
Keyword(s):  
Military Training ◽  
Structure And Function ◽  
Aquatic Systems ◽  
Ecosystem Structure ◽  
Population Declines ◽  
Exclusion Zone ◽  
Negative Effects ◽  
And Function ◽  
Ecosystem Structure And Function ◽  
Modern War

War is an ever-present force that has the potential to alter the biosphere. Here we review the potential consequences of modern war and military activities on ecosystem structure and function. We focus on the effects of direct conflict, nuclear weapons, military training, and military produced contaminants. Overall, the aforementioned activities were found to have overwhelmingly negative effects on ecosystem structure and function. Dramatic habitat alteration, environmental pollution, and disturbance contributed to population declines and biodiversity losses arising from both acute and chronic effects in both terrestrial and aquatic systems. In some instances, even in the face of massive alterations to ecosystem structure, recovery was possible. Interestingly, military activity was beneficial under specific conditions, such as when an exclusion zone was generated that generally resulted in population increases and (or) population recovery; an observation noted in both terrestrial and aquatic systems. Additionally, military technological advances (e.g., GPS technology, drone technology, biotelemetry) have provided conservation scientists with novel tools for research. Because of the challenges associated with conducting research in areas with military activities (e.g., restricted access, hazardous conditions), information pertaining to military impacts on the environment are relatively scarce and are often studied years after military activities have ceased and with no knowledge of baseline conditions. Additional research would help to elucidate the environmental consequences (positive and negative) and thus reveal opportunities for mitigating negative effects while informing the development of optimal strategies for rehabilitation and recovery.

scholarly journals Experimental Evaluation of Airlift Performance for Vertical Pumping of Water in Underground Mines

2021 ◽  
Author(s):  
Parviz Enany ◽  
Oleksandr Shevchenko ◽  
Carsten Drebenstedt
Keyword(s):  
Water Flow ◽  
High Efficiency ◽  
Experimental Studies ◽  
Theoretical Models ◽  
Injection System ◽  
Experimental Investigations ◽  
Flow Mode ◽  
New Device ◽  
Riser Pipe ◽  
Airlift Pump

AbstractThis paper presents experimental studies on the optimization of air–water flow in an airlift pump. Airlift pumps use compressed gas to verticall transport liquids and slurries. Due to the lack of theoretical equations for designing and predicting flow regimes, experimental investigations must be carried out to find the best condition to operate an airlift pump at high efficiency. We used a new air injection system and different submergence ratios to evaluate the output of a simple pump for vertical displacement of water in an underground mine. The tests were carried out in a new device with 5.64 m height and 10.2 cm circular riser pipe. Three air-jacket pipes, at different gas flows in the range of 0.002–0.09 m3/s were investigated with eight submergence ratios. It was found that with the same air flow rate, the most efficient flow of water was achieved when an air jacket with 3 mm diameter holes was used with a submergence ratio between 0.6 and 0.75. In addition, a comparison of practical results with two theoretical models proposed by other investigators showed that neither was able to accurately predict airlift performance in air–water flow mode.

scholarly journals Hosts of Raoiella indica Hirst (Acari: Tenuipalpidae) Native to the Brazilian Amazon

2017 ◽  
Vol 9 (4) ◽  
pp. 86 ◽  
Author(s):  
Cristina A. Gómez-Moya ◽  
Talita P. S. Lima ◽  
Elisângela G. F. Morais ◽  
Manoel G. C. Gondim Jr. ◽  
Gilberto J. De Moraes
Keyword(s):  
Plant Species ◽  
Native Species ◽  
Brazilian Amazon ◽  
Intrinsic Rate Of Increase ◽  
Native Plant ◽  
Instantaneous Rate ◽  
Net Reproductive Rate ◽  
Musa Paradisiaca ◽  
Rate Of Increase ◽  
Raoiella Indica

The expansion of red palm mite (RPM), Raoiella indica (Acari: Tenuipalpidae) in Brazil could impact negatively the native plant species, especially of the family Arecaceae. To determine which species could be at risk, we investigated the development and reproductive potential of R. indica on 19 plant species including 13 native species to the Brazilian Amazon (12 Arecaceae and one Heliconiaceae), and six exotic species, four Arecaceae, a Musaceae and a Zingiberaceae. Values of the instantaneous rate of increase (ri) were initially estimated at 7, 14, 21 and 28 days after infestation of each species. Higher values of ri (> 0.05) were determined on the Arecaceae Adonidia merrillii, Astrocaryum jauari, Cocos nucifera, Bactris simplicifrons, Mauritia flexuosa, Phoenix dactylifera and Socratea exorrhiza, and on the Heliconiaceae Heliconia psittacorum Sassy; these were classified as “potential primary hosts”. Lower, but still positive values of ri (0-0.05) were determined on the Arecaceae Bactris maraja, Oenocarpus bacaba, Oenocarpus bataua and on the Musaceae Musa × paradisiaca (Prata variety); these were classified as “potential secondary hosts”. Negative values of ri were determined for the remaining plants, i.e., the Arecaceae Astrocaryum aculeatum, Attalea maripa, Bactris gasipaes, Elaeis guineensis, Euterpe oleracea, Euterpe precatoria, and the Zingiberaceae Alpinia rosea; these were considered “non-hosts”. Species with ri < 0.05 were considered not to be threatened by the RPM. Biological parameters of RPM were evaluated on the plant species with positive ri (except B. maraja) and two native species with negative ri (E. oleracea and E. precatoria). Mean developmental time ranged from 14.7 days on C. nucifera to 21.4 days on Musa × paradisiaca, showing a significant influence of the plant substrate. Immature viability, oviposition rate, net reproductive rate (R0) and intrinsic rate of increase (rm) were affected by the plant species.

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