scholarly journals Intraspecific competition drives increased resource use diversity within a natural population

2006 ◽  
Vol 274 (1611) ◽  
pp. 839-844 ◽  
Author(s):  
Richard Svanbäck ◽  
Daniel I Bolnick
Keyword(s):  
Population Density ◽  
Intraspecific Competition ◽  
Resource Competition ◽  
Prey Availability ◽  
Natural Populations ◽  
Alternative Prey ◽  
Ecological Diversification ◽  
Evolutionary Diversification ◽  
Density Control ◽  
Niche Variation

Resource competition is thought to play a major role in driving evolutionary diversification. For instance, in ecological character displacement, coexisting species evolve to use different resources, reducing the effects of interspecific competition. It is thought that a similar diversifying effect might occur in response to competition among members of a single species. Individuals may mitigate the effects of intraspecific competition by switching to use alternative resources not used by conspecific competitors. This diversification is the driving force in some models of sympatric speciation, but has not been demonstrated in natural populations. Here, we present experimental evidence confirming that competition drives ecological diversification within natural populations. We manipulated population density of three-spine sticklebacks ( Gasterosteus aculeatus ) in enclosures in a natural lake. Increased population density led to reduced prey availability, causing individuals to add alternative prey types to their diet. Since phenotypically different individuals added different alternative prey, diet variation among individuals increased relative to low-density control enclosures. Competition also increased the diet–morphology correlations, so that the frequency-dependent interactions were stronger in high competition. These results not only confirm that resource competition promotes niche variation within populations, but also show that this increased diversity can arise via behavioural plasticity alone, without the evolutionary changes commonly assumed by theory.

scholarly journals Natural variation in social conditions affects male mate choosiness in the amphipod Gammarus roeselii

2021 ◽  
Author(s):  
Konrad Lipkowski ◽  
Sophie Steigerwald ◽  
Lisa M Schulte ◽  
Carolin Sommer-Trembo ◽  
Jonas Jourdan
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Natural Variation ◽  
Natural Populations ◽  
Social Background ◽  
Social Conditions ◽  
Background Information ◽  
Male Mating ◽  
Natural Environments ◽  
Male Mate

Abstract The extent of male mate choosiness is driven by a trade-off between various environmental factors associated with the costs of mate acquisition, quality assessment and opportunity costs. Our knowledge about natural variation in male mate choosiness across different populations of the same species, however, remains limited. In this study, we compared male mate choosiness across 10 natural populations of the freshwater amphipod Gammarus roeselii (Gervais 1835), a species with overall high male mating investments, and evaluated the relative influence of population density and sex ratio (both affecting mate availability) on male mate choosiness. We investigated amplexus establishment after separating mating pairs and presenting focal males with a novel, size-matched female from the same population. Our analysis revealed considerable effects of sex ratio and (to a lesser extent) population density on time until amplexus establishment (choosiness). Male amphipods are able to perceive variable social conditions (e.g., sex ratio) and modify their mating strategy accordingly: We found choosiness to be reduced in increasingly male-biased populations, whereas selectivity increases when sex ratio becomes female biased. With this, our study expands our limited knowledge on natural variations in male mate choosiness and illustrates the importance of sex ratio (i.e., level of competition) for male mating decisions in natural environments. Accounting for variation in sex ratios, therefore, allows envisioning a distinctive variation of choosiness in natural populations and highlights the importance of considering social background information in future behavioral studies.

An ecological explanation for hyperallometric scaling of reproduction

2021 ◽  
Author(s):  
Tomos Potter ◽  
Anja Felmy
Keyword(s):  
Body Size ◽  
Reproductive Output ◽  
Resource Competition ◽  
Natural Populations ◽  
Scaling Exponent ◽  
Wild Populations ◽  
Wet Season ◽  
Size Dependent ◽  
In The Wild ◽  
The Relationship

AbstractIn wild populations, large individuals have disproportionately higher reproductive output than smaller individuals. We suggest an ecological explanation for this observation: asymmetry within populations in rates of resource assimilation, where greater assimilation causes both increased reproduction and body size. We assessed how the relationship between size and reproduction differs between wild and lab-reared Trinidadian guppies. We show that (i) reproduction increased disproportionately with body size in the wild but not in the lab, where effects of resource competition were eliminated; (ii) in the wild, the scaling exponent was greatest during the wet season, when resource competition is strongest; and (iii) detection of hyperallometric scaling of reproduction is inevitable if individual differences in assimilation are ignored. We propose that variation among individuals in assimilation – caused by size-dependent resource competition, niche expansion, and chance – can explain patterns of hyperallometric scaling of reproduction in natural populations.

Regulation of space use in a solitary felid: population density or prey availability?

2006 ◽  
Vol 71 (3) ◽  
pp. 685-693 ◽  
Author(s):  
John F. Benson ◽  
Michael J. Chamberlain ◽  
Bruce D. Leopold
Keyword(s):  
Population Density ◽  
Prey Availability ◽  
Space Use

scholarly journals Recruitment sex ratios in gray-tailed voles (Microtus canicaudus) in response to density, sex ratio, and season

2003 ◽  
Vol 81 (8) ◽  
pp. 1306-1311 ◽  
Author(s):  
Monica L Bond ◽  
Jerry O Wolff ◽  
Sven Krackow
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Resource Competition ◽  
Sex Ratios ◽  
Female Offspring ◽  
High Population ◽  
Reproductive Value ◽  
High Population Density ◽  
Adult Sex Ratio ◽  
Sex Ratio Adjustment

We tested predictions associated with three widely used hypotheses for facultative sex-ratio adjustment of vertebrates using eight enclosed populations of gray-tailed voles, Microtus canicaudus. These were (i) the population sex ratio hypothesis, which predicts that recruitment sex ratios should oppose adult sex-ratio skews, (ii) the local resource competition hypothesis, which predicts female-biased recruitment at low adult population density and male-biased recruitment at high population density, and (iii) the first cohort advantage hypothesis, which predicts that recruitment sex ratios should be female biased in the spring and male biased in the autumn. We monitored naturally increasing population densities with approximately equal adult sex ratios through the spring and summer and manipulated adult sex ratios in the autumn and measured subsequent sex ratios of recruits. We did not observe any significant sex-ratio adjustment in response to adult sex ratio or high population density; we did detect an influence of time within the breeding season, with more female offspring observed in the spring and more male offspring observed in the autumn. Significant seasonal increases in recruitment sex ratios indicate the capacity of female gray-tailed voles to manipulate their offspring sex ratios and suggest seasonal variation in the relative reproductive value of male and female offspring to be a regular phenomenon.

scholarly journals Balancing selection maintains polymorphisms at neurogenetic loci in field experiments

2017 ◽  
Vol 114 (14) ◽  
pp. 3690-3695 ◽  
Author(s):  
Eija Lonn ◽  
Esa Koskela ◽  
Tapio Mappes ◽  
Mikael Mokkonen ◽  
Angela M. Sims ◽  
...  
Keyword(s):  
Reproductive Success ◽  
Population Density ◽  
Arginine Vasopressin ◽  
Field Experiments ◽  
Balancing Selection ◽  
Regulatory Region ◽  
Natural Populations ◽  
Myodes Glareolus ◽  
Sexual Antagonism ◽  
Reproductive Behaviors

Most variation in behavior has a genetic basis, but the processes determining the level of diversity at behavioral loci are largely unknown for natural populations. Expression of arginine vasopressin receptor 1a (Avpr1a) and oxytocin receptor (Oxtr) in specific regions of the brain regulates diverse social and reproductive behaviors in mammals, including humans. That these genes have important fitness consequences and that natural populations contain extensive diversity at these loci implies the action of balancing selection. In Myodes glareolus, Avpr1a and Oxtr each contain a polymorphic microsatellite locus located in their 5′ regulatory region (the regulatory region-associated microsatellite, RRAM) that likely regulates gene expression. To test the hypothesis that balancing selection maintains diversity at behavioral loci, we released artificially bred females and males with different RRAM allele lengths into field enclosures that differed in population density. The length of Avpr1a and Oxtr RRAMs was associated with reproductive success, but population density and the sex interacted to determine the optimal genotype. In general, longer Avpr1a RRAMs were more beneficial for males, and shorter RRAMs were more beneficial for females; the opposite was true for Oxtr RRAMs. Moreover, Avpr1a RRAM allele length is correlated with the reproductive success of the sexes during different phases of reproduction; for males, RRAM length correlated with the numbers of newborn offspring, but for females selection was evident on the number of weaned offspring. This report of density-dependence and sexual antagonism acting on loci within the arginine vasopressin–oxytocin pathway explains how genetic diversity at Avpr1a and Oxtr could be maintained in natural populations.

Effects of alternative and natural prey on body size, locomotion and dispersal of Neoseiulus bicaudus (Acari: Phytoseiidae)

2019 ◽  
Vol 24 (9) ◽  
pp. 1579-1591
Author(s):  
Jie Su ◽  
Min Liu ◽  
Zhen-Shi Fu ◽  
An-Di Zhu ◽  
Jian Ping Zhang
Keyword(s):  
Body Size ◽  
Prey Availability ◽  
Mass Rearing ◽  
Predatory Mite ◽  
The Body ◽  
Alternative Prey ◽  
Negative Effects ◽  
Natural Prey ◽  
Tetranychus Turkestani

Prey are very important for the mass rearing of natural enemies and can affect the efficiency and quality of natural enemy products. Locomotion is important in dispersal of predatory mites on plants, and such activity is affected by body size and prey availability. The study evaluates the effects of prey (alternative prey: Tyrophagus putrescentiae Schrank and natural prey: Tetranychus turkestani Ugarov & Nikolskii) on the body size, locomotion and dispersal of the predatory mite Neoseiulus bicaudus Wainstein. When fed the alternative prey, the body size and locomotion of N. bicaudus were significantly lower than when fed the natural prey. However, the dispersal of N. bicaudus fed the two prey types was similar. The results suggest that long-term feeding on alternative prey could decrease the body size and locomotion of N. bicaudus. Nevertheless, the negative effects of alternative prey did not appear to affect the dispersal of N. bicaudus. The likely reason is that the type of prey does not affect the ability of the predatory mite to locate spider mites. In other words, when it fed alternative prey, N. bicaudus could still successfully disperse and locate spider mite-infested plants in the same way as when fed the natural prey.

scholarly journals An experimental investigation of how intraspecific competition and phenotypic plasticity can promote the evolution of novel, complex phenotypes

2020 ◽  
Vol 131 (1) ◽  
pp. 76-87
Author(s):  
Nicholas A Levis ◽  
Carly G Fuller ◽  
David W Pfennig
Keyword(s):  
Phenotypic Plasticity ◽  
Intraspecific Competition ◽  
Morphological Plasticity ◽  
Standard Diet ◽  
Heritable Variation ◽  
Evolutionary Diversification ◽  
Evolutionary Innovation ◽  
Spadefoot Toad ◽  
Scaphiopus Holbrookii ◽  
Novel Complex

Abstract Intraspecific competition has long been considered a key driver of evolutionary diversification, but whether it can also promote evolutionary innovation is less clear. Here we examined the interplay between competition and phenotypic plasticity in fuelling the origins of a novel, complex phenotype – a distinctive carnivore morph found in spadefoot toad tadpoles (genus Spea) that specializes on fairy shrimp. We specifically sought to explore the possible origins of this phenotype by providing shrimp to Scaphiopus holbrookii tadpoles (the sister genus to Spea that does not produce carnivores) while subjecting them to competition for their standard diet of detritus. Previous research had shown that this species will eat shrimp when detritus is limited, and that these shrimp-fed individuals produce features that are redolent of a rudimentary Spea carnivore. In this study, we found that: (1) behavioural and morphological plasticity enabled some individuals to expand their diet to include shrimp; (2) there was heritable variation in this plasticity; and (3) individuals received a growth and development benefit by eating shrimp. Thus, novel resource use can arise via plasticity as an adaptive response to intraspecific competition. More generally, our results show how competition and plasticity may interact to pave the way for the evolution of complex, novel phenotypes, such as the distinctive carnivore morph in present-day Spea.

The population dynamics of Cardiaspina albitextura (Psyllidae).

1964 ◽  
Vol 12 (3) ◽  
pp. 362 ◽  
Author(s):  
LR Clark
Keyword(s):  
Population Dynamics ◽  
Population Density ◽  
Population Study ◽  
Intraspecific Competition ◽  
Limited Availability ◽  
Host Trees ◽  
Increase With Increase ◽  
Numerical Stabilization ◽  
Environmental Agencies ◽  
Population Numbers

During the last 16 years, the numbers of Cavdiaspina albitextura rose from low to high in many places, and either remained high or eventually resumed their original levels. In other places, the numbers of the psyllid remained low although they fluctuated considerably. The results of a population study which began in 1952 suggest that, in parts of the woodland colonized by C. albitextura, the stabilization of psyllid numbers occurred temporarily - in some areas at low mean levels of population density and in others at high mean levels. In other parts of the woodland, psyllid numbers changed progressively with time. The occurrence of numerical stabilization appeared to depend upon the extent of the mortality caused directly or indirectly by certain environmental agencies whose "deciding" or "conditioning" influence determined when and where stabilization was possible. At low psyllid densities, the principal conditioning agencies were probably the whole complex of species predacious on psyllid nymphs and eggs, and weather. At high psyllid densities, the conditioning agencies were the density of host trees, and wind. Providing that sufficient mortality was caused by the conditioning agencies, negative feed-back mechanisms were able to implement stabilization. At low psyllid densities, birds predacious on adult psyllids appeared to be the operative or "density-governing" agency. The intensity of their attacks, which tended to increase with increase in psyllid density, operated in a probabilistic manner to limit increase in population numbers. At high psyllid densities, food and space favourable for oviposition were the operative agencies. The limited availability of food and space brought into action a stabilizing mechanism which functioned automatically through forms of intraspecific competition.

scholarly journals Frequency dependence shapes the adaptive landscape of imperfect Batesian mimicry

2018 ◽  
Vol 285 (1876) ◽  
pp. 20172786 ◽  
Author(s):  
Susan D. Finkbeiner ◽  
Patricio A. Salazar ◽  
Sofía Nogales ◽  
Cassidi E. Rush ◽  
Adriana D. Briscoe ◽  
...  
Keyword(s):  
Relative Abundance ◽  
Complex Dynamics ◽  
Natural Populations ◽  
Batesian Mimicry ◽  
Biological Research ◽  
Adaptive Landscape ◽  
Alternative Prey ◽  
Frequency Dependent ◽  
Growing Body ◽  
Compelling Experimental Evidence

Despite more than a century of biological research on the evolution and maintenance of mimetic signals, the relative frequencies of models and mimics necessary to establish and maintain Batesian mimicry in natural populations remain understudied. Here we investigate the frequency-dependent dynamics of imperfect Batesian mimicry, using predation experiments involving artificial butterfly models. We use two geographically distinct populations of Adelpha butterflies that vary in their relative frequencies of a putatively defended model ( Adelpha iphiclus ) and Batesian mimic ( Adelpha serpa ). We found that in Costa Rica, where both species share similar abundances, Batesian mimicry breaks down, and predators more readily attack artificial butterfly models of the presumed mimic, A. serpa . By contrast, in Ecuador, where A. iphiclus (model) is significantly more abundant than A. serpa (mimic), both species are equally protected from predation. Our results provide compelling experimental evidence that imperfect Batesian mimicry is frequency-dependent on the relative abundance of models and mimics in natural populations, and contribute to the growing body of evidence that complex dynamics, such as seasonality or the availability of alternative prey, influence the evolution of mimetic traits.

Distinguishing error from chaos in ecological time series

1990 ◽  
Vol 330 (1257) ◽  
pp. 235-251 ◽  
Keyword(s):  
New York ◽  
Population Density ◽  
Sampling Error ◽  
Natural Populations ◽  
Real Data ◽  
Environmental Stochasticity ◽  
Population Variation ◽  
Data Sets ◽  
Spatial Effects ◽  
Low Dimensional

Over the years, there has been much discussion about the relative importance of environmental and biological factors in regulating natural populations. Often it is thought that environmental factors are associated with stochastic fluctuations in population density, and biological ones with deterministic regulation. We revisit these ideas in the light of recent work on chaos and nonlinear systems. We show that completely deterministic regulatory factors can lead to apparently random fluctuations in population density, and we then develop a new method (that can be applied to limited data sets) to make practical distinctions between apparently noisy dynamics produced by low-dimensional chaos and population variation that in fact derives from random (high-dimensional)noise, such as environmental stochasticity or sampling error. To show its practical use, the method is first applied to models where the dynamics are known. We then apply the method to several sets of real data, including newly analysed data on the incidence of measles in the United Kingdom. Here the additional problems of secular trends and spatial effects are explored. In particular, we find that on a city-by-city scale measles exhibits low-dimensional chaos (as has previously been found for measles in New York City), whereas on a larger, country-wide scale the dynamics appear as a noisy two-year cycle. In addition to shedding light on the basic dynamics of some nonlinear biological systems, this work dramatizes how the scale on which data is collected and analysed can affect the conclusions drawn.

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