Glossary

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P

Palaeoarctic
The biogeographic region comprising the landmass of Europe and Asia from its northern border to the Sahara and Himalayas.
Pampa(s)
The treeless plains of South America, south of the Amazon.
Parallel evolution
The evolution along similar lines of systematic groups that had been separated geographically at an earlier stage in their history.
Parasite
An organism that obtains its nutrients from one or a very few host individuals causing harm but not causing death immediately.
Parasitoid
Insects (mostly wasps and flies) in which the adults are free-living, but eggs are laid in, on or near an insect host (or rarely, a spider or isopod), after which the parasitoid larva develops in the host (itself usually a pre-adult), initially doing little apparent harm, but eventually consuming and killing the host before or during the pupal stage.
Partial refuges
Areas of prey habitat in which their consumption rate by predators is less than the average for the habitat as a whole, as a result of the predators' behavioral responses to the prey's spatial distribution.
Passive dispersal
Movement of seeds, spores or dispersive stages of animals caused by external agents such as wind current.
Patch dynamics
The concept of communities as consisting of a mosaic of patches within which abiotic disturbances and biotic interactions proceed.
Patchy habitat
A habitat within which there are significant spatial variations in suitability for the species under consideration.
Pathogen
A microorganism or virus that causes disease.
Permafrost
Layer of permanently frozen soil.
Permanent wilting point
The condition of a soil in which water is sufficiently unavailable to cause plants growing in it to wilt irrecoverably.
Perturbation approach
In community ecology, an experimental approach in which artificial disturbances are used to unravel species interactions.
Pest species
Simply: any species which we, as humans, consider undesirable. More explicitly: a species which competes with humans for food, fiber or shelter, transmits pathogens, feeds on people, or otherwise threatens human health, comfort or welfare.
Petiole
The stalk of a leaf.
pH
A scale of acidity (1 - 7) or alkalinity (7 - 14) derived from the logarithm of the concentration of hydrogen ions (10 - 1 - 10 - 14).
Phagocyte
White blood-corpuscle capable of destroying harmful bacteria.
Phenology
Strictly the study of periodic biological events; in practice often applied to periodic phenomena themselves, such as the lifetime pattern in an organism of growth, development and reproduction in relation to the seasons.
Phenotype
A visible, or otherwise measurable, physical or biochemical characteristic of an organism, resulting from the interaction between the genotype and the environment.
Pheromones
Chemicals released, usually in minute amounts, by one animal, that are detected by, and act as a signal to other members of the same species.
Phloem
A plant tissue in the veins (vascular bundles) of plants that is responsible for most of the transport of organic solutes.
Photoperiod
Length of the period of daylight each day.
Photosynthate
The energy-rich organic molecules produced during photosynthesis.
Photosynthesis
Utilization of the energy of sunlight to combine CO2 and water into sugars.
Photosynthetically active radiation (PAR)
Those wavelengths in the spectrum of radiation that are effective in photosynthesis.
Phyletic lines
Links drawn between present and past groups of organisms which imply their evolutionary relationships and derivation.
Phyllosphere
The microenvironment on or in the immediate neighborhood of a leaf.
Phylogeny
Evolutionary history of a taxonomic group.
Physiological time
A measure combining time and temperature and applied to ectothermic and poikilothermic organisms, reflecting the fact that growth and development in particular are dependent on environmental temperature and therefore require a period of time temperature rather than simply time for their completion.
Physiology
Study of the internal processes and activities of organisms.
Phytoalexins
Complex organic compounds produced by plants in response to infection and that are inhibitors of further growth by the pathogen.
Phytophagous
Feeding on plant material.
Placental mammal
Mammals which develop a persistent placenta, i.e. all mammals other than marsupials and monotremes.
Pleistocene
A geological era lasting from approximately 2 million to 10 000 years ago.
Pliocene
A geological era lasting from approximately 5 to 2 million years ago.
Pogonophoran
A marine invertebrate of the phylum Pogonophora.
Poikilotherm
An organism whose body temperature is strongly correlated with that of its external environment.
Polycentric distribution
The presence of a population, species or other taxonomic group in several widely separated places.
Polyclimax theory
The idea that succession leads to one of a variety of climaxes, depending on local environmental conditions.
Polymorphism
The existence within a species or population of different forms of individuals, beyond those that are the result simply of recurrent mutation.
Polyphagous
Consuming a wide range of types of food items.
Polysaccharide
A carbohydrate polymer made up of a chain of monosaccharides, e.g. starch, cellulose.
Population
A group of individuals of one species in an area, though the size and nature of the area is defined, often arbitrarily, for the purposes of the study being undertaken.
Population cycle
Changes in the numbers of individuals in a population which repeatedly oscillate between periods of high and low density.
Population density
The numbers in a population per unit area, or sometimes 'per unit volume', 'per leaf' or whatever seems appropriate.
Population dynamics
The variations in time and space in the sizes and densities of populations.
Population ecology
The study of the variations in time and space in the sizes and densities of populations, and of the factors causing those variations.
Population fluctuations
Variations over time in the size of a population.
Population pyramid
A means of illustrating the age structure of a population diagrammatically, by placing the youngest age class at the base and stacking successive age classes above it.
Population regulation
A tendency in a population for some factor to cause density to increase when it is low and to decrease when it is high.
Population vulnerability analysis (PVA)
An analysis, generally applied to populations or species in danger of extinction, of the population's chances of extinction.
Potential evapotranspiration
see Evapotranspiration.
Prairie grassland
A local, North American, name for the temperate grassland biome.
Precocity
Reproduction occurring early in the life and growth of an organism relative to other organisms of the same or related species that, relatively, delay reproduction.
Predation
The consumption of one organism, in whole or in part, by another, where the consumed organism is alive when the consumer first attacks it.
Predator
An organism that consumes other organisms, divisible into true predators, grazers, parasites and parasitoids.
Prevalence (of abundance)
The proportion or percentage of habitable sites or areas in which a particular species is present.
Prevalence of infection
The proportion, or percentage, of a population that is infected with a specific parasite.
Prey
An individual liable to be, or actually, consumed (and hence killed) by a predator.
Primary productivity
The rate at which biomass is produced per unit area by plants.
Production efficiency
The percentage of energy assimilated by an organism that becomes incorporated into new biomass.
Productivity
The rate at which biomass is produced per unit area by any class of organisms.
Prokaryote
A cell lacking a membrane-bound nucleus; a bacterium or cyanobacterium.
Propagule
A term used for a structure in a plant (occasionally used for invertebrates) from which a new individual may arise, e.g. seed, corm, bulb, cyst and which may often also be a unit of dispersal.
Protoplasm
Living matter.
Protozoan
Single-celled animal.
Pseudo-interference
A pattern of declining predator consumption rate with increasing predator density, reminiscent of the effects of mutual interference, but resulting from the aggregative response of the predator.
Pteridophytes
A division of the plant kingdom comprising ferns, horsetails, clubmosses and their allies. Plants with true stems, leaves and roots (diploid) reproducing by spores and alternating with a free-living inconspicuous sexual (haploid) generation (prothalli).

 
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