Reproductive ecology of the distylous species Houstonia longifolia: implications for conservation of a rare species

Distylous species typically experience self-incompatibility with one morph often having partial self-compatibility. Small populations may therefore experience greater rates of selfing/intramorph crosses leading to skewed morph ratios and reduced seed production. For the distylous species Houstonia longifolia Gaertn. (“imperiled” at its northwestern range limit in Alberta), we examined whether small populations were morph-biased and whether seed production was affected by population size, local density, plant size, morph type, and surrounding morph ratio. For focal plants in several populations, we measured size (height, number of stems) and local density (1 m2) of pins and thrums, with the focal plants collected for seed counts. Population size was estimated from densities in systematically located quadrats in each population. Morph ratios were pin-biased in small populations but were even to slightly thrum-biased in large populations. The critical population size for maintaining an equal morph ratio was ∼726 plants. Seed production was most influenced by the interaction between morph type and surrounding morph ratio, which were themselves influenced by population size (Allee effect). Seed production increased for thrums but decreased for pins as the proportion of surrounding pins increased, suggesting strong incompatibility. These results provide guidance on population size and morph ratios for conservation actions.

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Population size, habitat fragmentation, and the nature of adaptive variation in a stream fish

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2014.0370 ◽

2014 ◽

Vol 281 (1790) ◽

pp. 20140370 ◽

Cited By ~ 31

Author(s):

Dylan J. Fraser ◽

Paul V. Debes ◽

Louis Bernatchez ◽

Jeffrey A. Hutchings

Keyword(s):

Genetic Variation ◽

Habitat Fragmentation ◽

Population Size ◽

Brook Trout ◽

Small Populations ◽

Adaptive Genetic Variation ◽

Genetic Population ◽

Fragmented Populations ◽

Large Populations ◽

Adaptive Differentiation

Whether and how habitat fragmentation and population size jointly affect adaptive genetic variation and adaptive population differentiation are largely unexplored. Owing to pronounced genetic drift, small, fragmented populations are thought to exhibit reduced adaptive genetic variation relative to large populations. Yet fragmentation is known to increase variability within and among habitats as population size decreases. Such variability might instead favour the maintenance of adaptive polymorphisms and/or generate more variability in adaptive differentiation at smaller population size. We investigated these alternative hypotheses by analysing coding-gene, single-nucleotide polymorphisms associated with different biological functions in fragmented brook trout populations of variable sizes. Putative adaptive differentiation was greater between small and large populations or among small populations than among large populations. These trends were stronger for genetic population size measures than demographic ones and were present despite pronounced drift in small populations. Our results suggest that fragmentation affects natural selection and that the changes elicited in the adaptive genetic composition and differentiation of fragmented populations vary with population size. By generating more variable evolutionary responses, the alteration of selective pressures during habitat fragmentation may affect future population persistence independently of, and perhaps long before, the effects of demographic and genetic stochasticity are manifest.

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Population-size-dependent, age-structured branching processes linger around their carrying capacity

Journal of Applied Probability ◽

10.1017/s0021900200099265 ◽

2011 ◽

Vol 48 (A) ◽

pp. 249-260

Author(s):

Peter Jagers ◽

Fima C. Klebaner

Keyword(s):

Population Size ◽

Carrying Capacity ◽

Branching Process ◽

Branching Processes ◽

Critical Threshold ◽

Small Populations ◽

Size Dependent ◽

Large Populations ◽

Age Structured ◽

Process Context

Dependence of individual reproduction upon the size of the whole population is studied in a general branching process context. The particular feature under scrutiny is that of reproduction changing from supercritical in small populations to subcritical in large populations. The transition occurs when the population size passes a critical threshold, known in ecology as the carrying capacity. We show that populations either die out directly, never coming close to the carrying capacity, or grow quickly towards the carrying capacity, subsequently lingering around it for a time that is expected to be exponentially long in terms of a carrying capacity tending to infinity.

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Pollen limitation and reproduction varies with population size in experimental populations of Sabatia angularis (Gentianaceae)

Botany ◽

10.1139/b08-146 ◽

2009 ◽

Vol 87 (3) ◽

pp. 330-338 ◽

Cited By ~ 20

Author(s):

Rachel B. Spigler ◽

Shu-Mei Chang

Keyword(s):

Reproductive Success ◽

Population Size ◽

Intraspecific Competition ◽

Seed Set ◽

Pollen Limitation ◽

Small Populations ◽

Plant Populations ◽

Large Populations ◽

Fruit And Seed Set ◽

Supplemental Pollination

Individuals in large plant populations are expected to benefit from increased reproductive success relative to those in small populations because of the facilitative effects of large aggregations on pollination. As populations become small, the inability to attract sufficient numbers of pollinators can reduce reproduction via pollen limitation. This study experimentally tested whether such trends occur for the herbaceous biennial Sabatia angularis (L.) Pursh (Gentianaceae). We created artificial populations of varying size consisting of potted S. angularis plants in two field sites to determine whether population size affected mean fruit and seed set. We also examined whether population size affected the degree of pollen limitation using a supplemental pollination design in one of the sites. Our results showed that, on average, seed set was lower in large populations, not small populations, of S. angularis and that this result may be due to increased pollen limitation in large populations. We suggest that in certain contexts, small populations may enjoy reproductive advantages over large populations by escaping intraspecific competition for pollinators.

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Spatiotemporal Variations in Seed Set and Pollen Limitation in Populations of the Rare Generalist Species Polemonium caeruleum in Poland

Frontiers in Plant Science ◽

10.3389/fpls.2021.755830 ◽

2022 ◽

Vol 12 ◽

Author(s):

Justyna Ryniewicz ◽

Katarzyna Roguz ◽

Paweł Mirski ◽

Emilia Brzosko ◽

Mateusz Skłodowski ◽

...

Keyword(s):

Reproductive Success ◽

Population Size ◽

Seed Production ◽

Seed Set ◽

Pollen Limitation ◽

Monthly Precipitation ◽

Small Populations ◽

Flower Visitors ◽

Visitation Frequency ◽

Average Monthly Precipitation

A vast majority of angiosperms are pollinated by animals, and a decline in the number and diversity of insects often affects plant reproduction through pollen limitation. This phenomenon may be particularly severe in rare plant species, whose populations are shrinking. Here, we examined the variability in factors shaping reproductive success and pollen limitation in red-listed Polemonium caeruleum L. During a 5-year study in several populations of P. caeruleum (7–15, depending on year), we assessed the degree of pollen limitation based on differences in seed set between open-pollinated (control) and hand-pollinated flowers. We analysed the effects of flower visitors, population size, and meteorological data on plant reproductive success and pollen limitation. Our study showed that pollen limitation rarely affected P. caeruleum populations, and was present mainly in small populations. Pollen limitation index was negatively affected by the size of population, visitation frequency of all insects, and when considering the visitation frequency of individual groups, also by honeybee visits. Seed production in control treatment was positively influenced by the population size, average monthly precipitation in June and visits of hoverflies, while visits of honeybees, average monthly temperature in September, and average monthly precipitation in August influenced seed production negatively. As generalist plant P. caeruleum can be pollinated by diverse insect groups, however, in small populations their main visitors, the honeybees and bumblebees, may be less attracted, eventually leading to the disappearance of these populations. In pollination of P. caeruleum managed honeybees may play a dual role: while they are the most frequent and efficient flower visitors, their presence decreases seed set in open-pollinated flowers, which is most probably related to efficient pollen collection by these insects.

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Population-size-dependent, age-structured branching processes linger around their carrying capacity

Journal of Applied Probability ◽

10.1239/jap/1318940469 ◽

2011 ◽

Vol 48 (A) ◽

pp. 249-260 ◽

Cited By ~ 17

Author(s):

Peter Jagers ◽

Fima C. Klebaner

Keyword(s):

Population Size ◽

Carrying Capacity ◽

Branching Process ◽

Branching Processes ◽

Critical Threshold ◽

Small Populations ◽

Size Dependent ◽

Large Populations ◽

Age Structured ◽

Process Context

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Different Evolutionary Paths to Complexity for Small and Large Populations of Digital Organisms

10.1101/049767 ◽

2016 ◽

Author(s):

Thomas LaBar ◽

Christoph Adami

Keyword(s):

Population Size ◽

Genetic Drift ◽

Experimental Evolution ◽

Small Populations ◽

Strong Selection ◽

Evolution Of Complexity ◽

Phenotypic Complexity ◽

Novel Traits ◽

Large Populations ◽

Evolutionary Paths

AbstractA major aim of evolutionary biology is to explain the respective roles of adaptive versus non-adaptive changes in the evolution of complexity. While selection is certainly responsible for the spread and maintenance of complex phenotypes, this does not automatically imply that strong selection enhances the chance for the emergence of novel traits, that is, the origination of complexity. Population size is one parameter that alters the relative importance of adaptive and non-adaptive processes: as population size decreases, selection weakens and genetic drift grows in importance. Because of this relationship, many theories invoke a role for population size in the evolution of complexity. Such theories are difficult to test empirically because of the time required for the evolution of complexity in biological populations. Here, we used digital experimental evolution to test whether large or small asexual populations tend to evolve greater complexity. We find that both small and large—but not intermediate-sized—populations are favored to evolve larger genomes, which provides the opportunity for subsequent increases in phenotypic complexity. However, small and large populations followed different evolutionary paths towards these novel traits. Small populations evolved larger genomes by fixing slightly deleterious insertions, while large populations fixed rare beneficial insertions that increased genome size. These results demonstrate that genetic drift can lead to the evolution of complexity in small populations and that purifying selection is not powerful enough to prevent the evolution of complexity in large populations.Author SummarySince the early days of theoretical population genetics. scientists have debated the role of population size in shaping evolutionary dynamics. Do large populations possess an evolutionary advantage towards complexity due to the strength of natural selection in these populations? Or do small populations have the advantage, as genetic drift allows for the exploration of fitness landscapes inaccessible to large populations? There are many theories that predict whether large or small populations–those with strong selection or those with strong drift–should evolve the greatest complexity. Here, we use digital experimental evolution to examine the interplay between population size and the evolution of complexity. We found that genetic drift could lead to increased genome size and phenotypic complexity in very small populations. However, large populations also evolved similar large genomes and complexity. Small populations evolved larger genomes through the fixation of slightly deleterious insertions, while large populations utilized rare beneficial insertions. Our results suggest that both strong drift and strong selection can allow populations to evolve similar complexity, but through different evolutionary trajectories.

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Evolutionary genetics of small populations

10.1093/oso/9780198783398.003.0002 ◽

2017 ◽

Author(s):

Richard Frankham ◽

Jonathan D. Ballou ◽

Katherine Ralls ◽

Mark D. B. Eldridge ◽

Michele R. Dudash ◽

...

Keyword(s):

Genetic Diversity ◽

Population Size ◽

Evolutionary Genetics ◽

Small Population ◽

Small Populations ◽

Effective Population ◽

Genetic Management ◽

Evolutionary Genetic ◽

Loss Of Genetic Diversity ◽

Number Of Individuals

Genetic management of fragmented populations involves the application of evolutionary genetic theory and knowledge to alleviate problems due to inbreeding and loss of genetic diversity in small population fragments. Populations evolve through the effects of mutation, natural selection, chance (genetic drift) and gene flow (migration). Large outbreeding, sexually reproducing populations typically contain substantial genetic diversity, while small populations typically contain reduced levels. Genetic impacts of small population size on inbreeding, loss of genetic diversity and population differentiation are determined by the genetically effective population size, which is usually much smaller than the number of individuals.

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Likelihoods and Simulation Methods for a Class of Nonneutral Population Genetics Models

Genetics ◽

10.1093/genetics/159.2.853 ◽

2001 ◽

Vol 159 (2) ◽

pp. 853-867 ◽

Cited By ~ 2

Author(s):

Peter Donnelly ◽

Magnus Nordborg ◽

Paul Joyce

Keyword(s):

Population Genetics ◽

Population Size ◽

Mutant Allele ◽

Mutation Rates ◽

Simulation Methods ◽

Large Populations ◽

Selection Intensities ◽

Infinite Alleles Model

Abstract Methods for simulating samples and sample statistics, under mutation-selection-drift equilibrium for a class of nonneutral population genetics models, and for evaluating the likelihood surface, in selection and mutation parameters, are developed and applied for observed data. The methods apply to large populations in settings in which selection is weak, in the sense that selection intensities, like mutation rates, are of the order of the inverse of the population size. General diploid selection is allowed, but the approach is currently restricted to models, such as the infinite alleles model and certain K-models, in which the type of a mutant allele does not depend on the type of its progenitor allele. The simulation methods have considerable advantages over available alternatives. No other methods currently seem practicable for approximating likelihood surfaces.

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