Competition and evolutionary stability of plants in a spatially structured habitat

We modelled the population dynamics of two types of plants with limited dispersal living in a lattice structured habitat. Each site of the square lattice model was either occupied by an individual or vacant. Each individual reproduced to its neighbors. We derived a criterion for the invasion of a rare type into a population composed of a resident type based on a pair-approximation method, in which the dynamics of both average densities and the nearest neighbor correlations were considered. Based on this invasibility criterion, we showed that, when there is a tradeoff between birth and death rates, the evolutionarily stable type is the one that has the highest ratio of birth rate to mortality. If these types are different species, they form segregated spatial patterns in the lattice model in which intraspecific competitive interactions occur more frequently than interspecific interactions. However, stable coexistence is not possible in the lattice model contrary to results from completely mixed population models. This clearly shows that the casual conclusion, based on traditional well mixed population models, that different species can coexist if intraspecific competition is stronger than interspecific competition, does not hold for spatially structured population models.     

Analyses of spatial patterns and population processes of clonal plants

The nonrandom spatial structure of terrestrial plants is formed by ecological interactions and reproduction with a limited dispersal range, and in turn this may strongly affect population dynamics and population genetics. The traditional method of modelling in population ecology is either to neglect spatial pattern (e.g. in transition matrix models) or to do straightforward computer simulation. We review here three analytical mothods to deal with plant populations in a lattice-structured habitat, which propagate both by seeds that scatter over the whole habitat and by vegetative reproduction (producing runners, rhizomes, etc.) to neighboring vacant sites. [1]Dynamics of global and local densities: Dynamical equations of population density considering nearest-neighbor correlation (spatial clumping) are developed as the joint dynamics of global average density and local density (comparable to mean crowding) based onpair approximation. If there is a linear trade-off between seed production and vegetative reproduction, the equilibrium abundance of the population may be maximized by engaging both means of reproduction. This result is accurately predicted by the pair approximation method, but not by mean-field approximation (neglect of spatial structure). [2]Cluster size distributions: Using global and local densities obtained by pair approximation, we predicted cluster size distribution, i.e. the number of clusters of occupied sites of various sizes. [3]Clonal identity probability decreasing with distance: Multi-locus measurement of allozymes or other neutral molecular markers tells us whether or not a given pair of individuals belong to the same clone. From the pattern of clonal identity probability decreasing with the distance between ramets, we can estimate the relative importance of two modes of reproduction: vegetative propagation and sexual seed production.     

Lattice population dynamics for plants with dispersing seeds and Vegetative propagation

The population dynamics of plants in a lattice structured habitat are studied theoretically. Plants are assumed to propagate both by producing seeds that scatter over the population and by vegetative reproduction by extending runners, rhizomes, or roots, to neighboring vacant sites. In addtion, the seed production rate may be dependent on the local density in the neighborhood, indicating beneficial or harmful crowding effects. Two sets of population dynamical equation(s) are derived: one based onmean-field approximation and the other based onpair approximation (tracing both global and local densities simultaneously). We examine the accuracy of these approximate dynamics by comparing them with direct computer simulation of the stochastic lattice model. Pair approximation is much more accurate than mean-field approximation. Mean-field approximation overestimates the parameter range for persistence if crowding effects on seed production are harmful or weakly beneficial, but underestimates it if crowding effects are highly beneficial. Dynamics may show bistability (both population persistence and extinction) if the effect of crowding is strongly beneficial. If there is a linear trade-off between seed production and vegetative reproduction, the equilibrium abundance of the population may be maximised by a mixture of seed production and vegetative reproduction, rather than by pure seed production or by pure vegetative reproduction. This result is correctly predicted by pair approximation but not by mean-field approximation.     

Evolution of litter size

Summary Theories on the evolution of litter size among organisms were reexamined. The competition theories, including that based on ther−K-selection hypothesis, could not explain well why low-fecundity strategies have often evolved in stressful environments such as mountain streams, deep sea and the antarctic, where interspecies competition is considered to be lax. The theory, based on It?'s (1980) concept of theprocurability of food by the young, was considered to have greater generality because it could explain not only the above-mentioned cases but also those where small litter size is observed in habitats with high species diversity (where interspecific competition may be keen), such as tropical rain forest. Examination of the process of selection of high-fecundity and low-fecundity genotypes also suggested that the procurability of food by the young can best explain the evolution of low-fecundity. The concept of density-induced dispersal and a distinction between density-dependent and density-independent predation pressures should be incorporated into our discussions on the evolution of reproductive rates. This work was supported in part by Grant-in-Aid No. 439017 from the Ministry of Education, Science and Culture.     

Social work for vulnerable and marginalized people during COVID-19 in Japan

During the Coronavirus disease pandemic (COVID-19), working conditions became increasingly difficult for social workers, as they had to deal with new challenges and added workloads. This study describes the difficulties faced by social workers of the Self-Reliance Support System in Japan and clarifies the solution for each difficulty while conducting their duties to support vulnerable people during COVID-19. To this end, we conducted an open-ended questionnaire survey and an interview survey. The data were analyzed using qualitative coding. The results showed that the difficulties faced in consultation support work included supporting hitherto socially invisible groups such as sole traders and foreigners. Social workers also faced an ethical dilemma, as they could not provide support to clients who “did not try to solve their problems” or for whom “interventional attempts did not lead to counseling support” and who only sought benefits at the risk of becoming isolated and impoverished. Following this, consultants collaborated to resolve such difficulties while maximizing the use of various local resources. The study's findings clarify that it would be effective to understand the difficulties faced by social workers to obtain hints toward their resolution.