Isodar is a theory of habitat selection in population biology proposed by Douglas W. Morris. The theory underscores the importance of the abundance and thus competition between the members of the same species in selecting habitats. The name "isodar" stems from "iso" in Latin meaning same and "dar" from Darwin. [1]
An isodar, or habitat isodar, is a theory in evolutionary ecology developed in the late 1980s by Douglas W. Morris. [2] [3] Isodars model density-dependent habitat selection for one or two species in two habitats according to the ideal free and ideal despotic distributions. Isodar is a two-part word: "iso" meaning equal in Latin; "dar" for Darwinian evolution, and is defined as all combinations of population densities in habitats A and B such that both habitats offer the same fitness reward.
Animals displaying an ideal free distribution distribute themselves among patches (sources of a resource) in such a way that each individual get the same amount of the resource. For example, if food is twice as abundant in habitat A compared to habitat B, the ideal free distribution-based model would predict that there will accordingly be twice as many animals competing for food in habitat A compared to habitat B. If the total number of animals is considered to be variable, there are two ways this can be plotted on a two-dimensional Cartesian graph. One way is to plot two lines on a graph of fitness vs. density of individuals. This graph can be used to predict the density of individuals at any given level of fitness. The second is to plot the density of individuals in habitat A vs. the density of individuals in habitat B when the fitness of all individuals is equal. The line in this second graph is an isodar line.
Ideal free isodars predict that a species density in habitat A will increase linearly with its density in habitat B so that each individual in the species has the same fitness. If habitat A has higher quality resources than habitat B, then proportionately more individuals would be in habitat A then in habitat B. This can be shown on either a Fitness-Density graph (Figure 1) or a graph of density in two habitats (Figure 2).
Isodars can be used to study density-dependent habitat selection between two species competing for two habitats. Species will equilibrate between the two habitats two maintain equal fitness within their own species and avoid competition with the other species. [4] Isodars have also been used to show the effect of human habitat selection on biodiversity. [5] They can also be employed to examine the cost and density dependence of habitat selection in a population. [6]
Criticism leveled against the method includes the fact that in attempting to condense a very complex combination of parameters into the single metric of population density, misleading conclusions about the underlying dynamics may be suggested or supported. [7]
Theoretical ecology is the scientific discipline devoted to the study of ecological systems using theoretical methods such as simple conceptual models, mathematical models, computational simulations, and advanced data analysis. Effective models improve understanding of the natural world by revealing how the dynamics of species populations are often based on fundamental biological conditions and processes. Further, the field aims to unify a diverse range of empirical observations by assuming that common, mechanistic processes generate observable phenomena across species and ecological environments. Based on biologically realistic assumptions, theoretical ecologists are able to uncover novel, non-intuitive insights about natural processes. Theoretical results are often verified by empirical and observational studies, revealing the power of theoretical methods in both predicting and understanding the noisy, diverse biological world.
Autecology is an approach in ecology that seeks to explain the distribution and abundance of species by studying interactions of individual organisms with their environments. An autecological approach differs from both community ecology (synecology) and population ecology by greater recognition of the species-specific adaptations of individual animals, plants or other organisms, and of environmental over density-dependent influences on species distributions. Autecological theory relates the species-specific requirements and environmental tolerances of individuals to the geographic distribution of the species, with individuals tracking suitable conditions, having the capacity for migration at at least one stage in their life cycles. Autecology has a strong grounding in evolutionary theory, including the theory of punctuated equilibrium and the recognition concept of species.
This glossary of ecology is a list of definitions of terms and concepts in ecology and related fields. For more specific definitions from other glossaries related to ecology, see Glossary of biology, Glossary of evolutionary biology, and Glossary of environmental science.
In biology, polymorphism is the occurrence of two or more clearly different morphs or forms, also referred to as alternative phenotypes, in the population of a species. To be classified as such, morphs must occupy the same habitat at the same time and belong to a panmictic population.
Frequency-dependent selection is an evolutionary process by which the fitness of a phenotype or genotype depends on the phenotype or genotype composition of a given population.
In evolutionary biology, inclusive fitness is one of two metrics of evolutionary success as defined by W. D. Hamilton in 1964:
Evolutionary game theory (EGT) is the application of game theory to evolving populations in biology. It defines a framework of contests, strategies, and analytics into which Darwinian competition can be modelled. It originated in 1973 with John Maynard Smith and George R. Price's formalisation of contests, analysed as strategies, and the mathematical criteria that can be used to predict the results of competing strategies.
Biological dispersal refers to both the movement of individuals from their birth site to their breeding site, as well as the movement from one breeding site to another . Dispersal is also used to describe the movement of propagules such as seeds and spores. Technically, dispersal is defined as any movement that has the potential to lead to gene flow. The act of dispersal involves three phases: departure, transfer, settlement and there are different fitness costs and benefits associated with each of these phases. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population genetics, and species distribution. Understanding dispersal and the consequences both for evolutionary strategies at a species level, and for processes at an ecosystem level, requires understanding on the type of dispersal, the dispersal range of a given species, and the dispersal mechanisms involved.
Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment, such as birth and death rates, and by immigration and emigration.
Evolutionary ecology lies at the intersection of ecology and evolutionary biology. It approaches the study of ecology in a way that explicitly considers the evolutionary histories of species and the interactions between them. Conversely, it can be seen as an approach to the study of evolution that incorporates an understanding of the interactions between the species under consideration. The main subfields of evolutionary ecology are life history evolution, sociobiology, the evolution of interspecific interactions and the evolution of biodiversity and of ecological communities.
The Allee effect is a phenomenon in biology characterized by a correlation between population size or density and the mean individual fitness of a population or species.
Michael L. Rosenzweig is a professor of ecology and evolutionary biology at the University of Arizona who has developed and popularized the concept of Reconciliation ecology. He received his Ph.D in zoology at the University of Pennsylvania in 1966 and has gone on to hold a number of positions around the United States.
A population can be described as being in an evolutionarily stable state when that population's "genetic composition is restored by selection after a disturbance, provided the disturbance is not too large". This population as a whole can be either monomorphic or polymorphic. This is now referred to as convergent stability.
Intraspecific competition is an interaction in population ecology, whereby members of the same species compete for limited resources. This leads to a reduction in fitness for both individuals, but the more fit individual survives and is able to reproduce. By contrast, interspecific competition occurs when members of different species compete for a shared resource. Members of the same species have rather similar requirements for resources, whereas different species have a smaller contested resource overlap, resulting in intraspecific competition generally being a stronger force than interspecific competition.
Human behavioral ecology (HBE) or human evolutionary ecology applies the principles of evolutionary theory and optimization to the study of human behavioral and cultural diversity. HBE examines the adaptive design of traits, behaviors, and life histories of humans in an ecological context. One aim of modern human behavioral ecology is to determine how ecological and social factors influence and shape behavioral flexibility within and between human populations. Among other things, HBE attempts to explain variation in human behavior as adaptive solutions to the competing life-history demands of growth, development, reproduction, parental care, and mate acquisition.
Species distribution —or speciesdispersion — is the manner in which a biological taxon is spatially arranged. The geographic limits of a particular taxon's distribution is its range, often represented as shaded areas on a map. Patterns of distribution change depending on the scale at which they are viewed, from the arrangement of individuals within a small family unit, to patterns within a population, or the distribution of the entire species as a whole (range). Species distribution is not to be confused with dispersal, which is the movement of individuals away from their region of origin or from a population center of high density.
In ecology, an ideal free distribution (IFD) is a theoretical way in which a population's individuals distribute themselves among several patches of resources within their environment, in order to minimize resource competition and maximize fitness. The theory states that the number of individual animals that will aggregate in various patches is proportional to the amount of resources available in each. For example, if patch A contains twice as many resources as patch B, there will be twice as many individuals foraging in patch A as in patch B.
Source–sink dynamics is a theoretical model used by ecologists to describe how variation in habitat quality may affect the population growth or decline of organisms.
In ecology, the occupancy–abundance (O–A) relationship is the relationship between the abundance of species and the size of their ranges within a region. This relationship is perhaps one of the most well-documented relationships in macroecology, and applies both intra- and interspecifically. In most cases, the O–A relationship is a positive relationship. Although an O–A relationship would be expected, given that a species colonizing a region must pass through the origin and could reach some theoretical maximum abundance and distribution, the relationship described here is somewhat more substantial, in that observed changes in range are associated with greater-than-proportional changes in abundance. Although this relationship appears to be pervasive, and has important implications for the conservation of endangered species, the mechanism(s) underlying it remain poorly understood
The body size-species richness distribution is a pattern observed in the way taxa are distributed over large spatial scales. The number of species that exhibit small body size generally far exceed the number of species that are large-bodied. Macroecology has long sought to understand the mechanisms that underlie the patterns of biodiversity, such as the body size-species richness pattern.