Density‐dependent prey behaviours and mutable predator foraging modes induce Allee effects and over‐prediction of prey mortality rates

2020 ◽  
Vol 65 (10) ◽  
pp. 1752-1764
Author(s):  
Zachary A. Siders ◽  
Robert N. M. Ahrens ◽  
Micheal S. Allen ◽  
Carl J. Walters
Keyword(s):  
Mortality Rates ◽  
Allee Effects ◽  
Density Dependent ◽  
Foraging Modes ◽  
Predator Foraging

Production and Population Dynamics of the Crayfish Orconectes virilis in Three Michigan Lakes

1977 ◽  
Vol 34 (11) ◽  
pp. 2030-2040 ◽  
Author(s):  
Walter T. Momot ◽  
Howard Gowing
Keyword(s):  
Population Dynamics ◽  
Growth Rates ◽  
Age Groups ◽  
Mortality Rates ◽  
Reproductive Age ◽  
Annual Production ◽  
Effective Density ◽  
Orconectes Virilis ◽  
Brood Stock ◽  
Density Dependent

Fluctuations in mortality rather than in growth rates produced most of the year-to-year differences in biomass accumulation of three different populations of the crayfish Orconectes virilis. Yearly biomass changes resulted from density-dependent control of mortality and fecundity during certain portions of the life cycle. Density-dependent changes in mortality rates controlled population size for adults in all lakes and for young-of-the-year in two of the three study lakes. Growth rates were much less responsive to fluctuating densities. Disparity between the number of ovarian and attached eggs increased as density of age I+ crayfish increased. This provided a strong density regulator on fecundity. Differences occurred in the number of recruits produced by a brood stock that survive to the end of the first growing season in the various lakes. Yet the number of females surviving to reproductive age 2 yr later was strongly regulated. Strong population regulation produced two female recruits of breeding age for every two–six parental breeding females. The high biomass and production levels of crayfish discovered in West Lost Lake in 1962–63 also occurred in the other area lakes. Higher but variable levels of recruitment resulted in larger standing crops and production in West Lost lake. This resulted from less effective density controls on the mortality rates of younger age-groups in that lake. Despite great variation in biomass of from 46 to 213 kg/ha and annual production from 60 to 142 kg/ha, the annual turnover ratio of the biomass was found to vary only between 0.94 and 1.53. Key words: crayfish, Orconectes virilis, population dynamics, annual production, Michigan lakes

Effect of Stocking Density on the Survival, Growth, and Dispersal of Steelhead Trout Fry (Salmo gairdneri)

1987 ◽  
Vol 44 (2) ◽  
pp. 271-281 ◽  
Author(s):  
Jeremy M. B. Hume ◽  
Eric A. Parkinson
Keyword(s):  
British Columbia ◽  
Overall Survival ◽  
Stocking Density ◽  
Mortality Rates ◽  
Wild Fish ◽  
Density Effect ◽  
Salmo Gairdneri ◽  
Steelhead Trout ◽  
Density Dependent ◽  
Coastal British Columbia

In a coastal British Columbia stream a stocking density of between 0.3 and 0.7 fry/m2 maximized the production of steelhead trout (Salmo gairdneri) parr and smolts. A severe autumn flood doubled the mortality rates of fry stocked at densities of 0.7 fry/m2 or higher but had little effect on fry stocked at lower densities (<0.15 fry/m2). Overall survival to smolts appeared to be lower than measured elsewhere for wild fish (2 vs. 4.5 – 18%). The proportion (<10%) of surviving fry found below the stocked sections was considered to be an indicator of potential displacement mortality in streams with no vacant downstream areas. This downstream dispersal was not density dependent and was small in comparison with the mortality of nondispersing fish. Although initial fry and parr sizes were density dependent, there was no detectable density effect on older parr or smolt sizes.

scholarly journals Modeling the effects of density dependent emigration, weak Allee effects, and matrix hostility on patch-level population persistence

2020 ◽  
Vol 17 (2) ◽  
pp. 1718-1742 ◽  
Author(s):  
James T. Cronin ◽  
◽  
Nalin Fonseka ◽  
Jerome Goddard II ◽  
Jackson Leonard ◽  
...  
Keyword(s):  
Population Persistence ◽  
Level Population ◽  
Allee Effects ◽  
Density Dependent ◽  
Effects Of Density

scholarly journals When higher carrying capacities lead to faster propagation

2018 ◽  
Author(s):  
Marjorie Haond ◽  
Thibaut Morel-Journel ◽  
Eric Lombaert ◽  
Elodie Vercken ◽  
Ludovic Mailleret ◽  
...  
Keyword(s):  
Carrying Capacity ◽  
Invasion Biology ◽  
Reaction Diffusion Equations ◽  
Positive Density ◽  
Allee Effects ◽  
Demographic Stochasticity ◽  
Positive Dependence ◽  
Density Dependent ◽  
Temporal Models ◽  
Density Dependent Dispersal

AbstractThis preprint has been reviewed and recommended by Peer Community In Ecology (https://dx.doi.org/10.24072/pci.ecology.100004). Finding general patterns in the expansion of natural populations is a major challenge in ecology and invasion biology. Classical spatio-temporal models predict that the carrying capacity (K) of the environment should have no influence on the speed (v) of an expanding population. We tested the generality of this statement with reaction-diffusion equations, stochastic individual-based models, and microcosms experiments with Trichogramma chilonis wasps. We investigated the dependence between K and v under different assumptions: null model (Fisher-KPP-like assumptions), strong Allee effects, and positive density-dependent dispersal. These approaches led to similar and complementary results. Strong Allee effects, positive density-dependent dispersal and demographic stochasticity in small populations lead to a positive dependence between K and v. A positive correlation between carrying capacity and propagation speed might be more frequent than previously expected, and be the rule when individuals at the edge of a population range are not able to fully drive the expansion.

scholarly journals Effects of phenological synchronization on caterpillar early-instar survival under a changing climate

2018 ◽  
Vol 48 (3) ◽  
pp. 247-254 ◽  
Author(s):  
Emma Despland
Keyword(s):  
Population Dynamics ◽  
Host Plants ◽  
Larval Mortality ◽  
Mortality Rates ◽  
Chemical Defenses ◽  
Population Fluctuations ◽  
Density Dependent ◽  
Early Instar ◽  
Species Specific ◽  
Very High

Early-instar caterpillars experience very high and often very variable mortality; if it is density dependent, it can be a key factor in outbreak dynamics. Plant physical and chemical defenses can be extremely effective against young caterpillars, even of specialists. Phenological asynchrony with host plants can lead to dispersal and mortality in the early instars and increased predation or poor nutrition in later instars. Predation on early-instar larvae (including cannibalism) can be extremely high, parasitism appears generally low, and pathogens acquired early in larval development can lead to high mortality in later stadia. Four well-studied species reveal very different roles of early-instar mortality in population dynamics. In spruce budworm and gypsy moth, early-instar mortality rates can be very high; they do not drive outbreak cycles because density dependence is weak, but can modulate cycles and contribute to outbreak size and duration. For the autumnal moth, early-instar survival depends on host plant synchrony, but may or may not be density dependent. For monarch butterflies, the relative importance of larval mortality rates in population dynamics remains unclear. Tritrophic interactions between herbivores, host plants, natural enemies, and microbes play complex and species-specific roles in early-instar ecology, leading to emergent dynamics in population fluctuations. The phenology of these relationships is often poorly understood, making their responses to climate change unpredictable.

scholarly journals Can't live with them, can't live without them? Balancing mating and competition in two-sex populations

2017 ◽  
Vol 284 (1865) ◽  
pp. 20171999 ◽  
Author(s):  
Aldo Compagnoni ◽  
Kenneth Steigman ◽  
Tom E. X. Miller
Keyword(s):  
Sex Ratio ◽  
Mating Success ◽  
Sex Ratios ◽  
Structured Populations ◽  
Allee Effects ◽  
Mate Finding ◽  
Frequency Dependent ◽  
Density Dependent ◽  
Positive Effects ◽  
Demographic Processes

Two-sex populations are usually studied through frequency-dependent models that describe how sex ratio affects mating, recruitment and population growth. However, in two-sex populations, mating and recruitment should also be affected by density and by its interactions with the sex ratio. Density may have positive effects on mating (Allee effects) but negative effects on other demographic processes. In this study, we quantified how positive and negative inter-sexual interactions balance in two-sex populations. Using a dioecious grass ( Poa arachnifera ), we established experimental field populations that varied in density and sex ratio. We then quantified mating success (seed fertilization) and non-mating demographic performance, and integrated these responses to project population-level recruitment. Female mating success was positively density-dependent, especially at female-biased sex ratios. Other demographic processes were negatively density-dependent and, in some cases, frequency-dependent. Integrating our experimental results showed that mate-finding Allee effects dominated other types of density-dependence, giving rise to recruitment that increased with increasing density and peaked at intermediate sex ratios, reflecting tension between seed initiation (greater with more females) and seed viability (greater with more males). Our results reveal, for the first time, the balance of positive and negative inter-sexual interactions in sex-structured populations. Models that account for both density- and sex ratio dependence, particularly in mating, may be necessary for understanding and predicting two-sex population dynamics.

Density-dependent sex ratio in Echinomermella matsi (Nematoda), a parasite of the sea urchin Strongylocentrotus droebachiensis

Parasitology ◽  
1996 ◽  
Vol 112 (1) ◽  
pp. 105-112 ◽  
Author(s):  
A. Stien ◽  
O. Halvorsen ◽  
H. P. Leinaas
Keyword(s):  
Sex Ratio ◽  
Density Dependence ◽  
Sea Urchin ◽  
Developmental Rate ◽  
Mortality Rates ◽  
Strongylocentrotus Droebachiensis ◽  
Male Dominance ◽  
Female Dominance ◽  
Density Dependent ◽  
Adult Sex Ratio

SUMMARYWe investigated the adult sex ratio in 70 infrapopulations of the nematode Echinomermella matsi, a parasite of the green sea urchin Strongylocentrotus droebachiensis. The adult sex ratio was skewed towards female dominance at low adult intensity and towards male dominance at high adult intensity. We hypothesize that this is due to differences between the sexes in development and mortality rates, or that female recruitment is density dependent. A model with differences between the sexes in developmental and mortality rates may develop the observed sex ratios if the female developmental and mortality rates are several times that of the males. A large difference in developmental rates between the sexes appears unreasonable because the developmental rate for both sexes is low, and the predicted low female life-expectancy is unlikely because the males appear to accumulate in infrapopulations as the females age. Density dependence of female numbers is, however, supported by a significantly lower female recruitment in infrapopulations with old females. We also find that the mean male length is negatively related to measures of crowding, thereby supporting the hypothesis that competition is of importance in E. matsi infrapopulations. A female bias at low intensities of infection, a density dependence in female recruitment and the taxonomic position of E. matsi indicate that sex may be environmentally determined in this nematode.

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