Glossary

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H

Habitat
Place where a microorganism, plant or animal lives.
Habitat diversity
The range of habitats present in a region.
Halophyte
A plant that tolerates very salty soil.
Handling time
The length of time a predator spends in pursuing, subduing and consuming a prey item and then preparing itself for further prey searching.
Hardening
A process by which the tolerance of extreme conditions, e.g. cold or drought, is increased by prior exposure to the same but less extreme conditions.
Haustoria
Branches of parasitic plants or fungi which enter the tissues or cells of the host.
Hemiparasite
Plants which are photosynthetic but form connections with the roots or stems of other plant species, drawing most or all of their water and mineral nutrient resources from their host.
Herbicide
A chemical or biological preparation which kills plants.
Herbivory
The consumption of living plant material.
Heritable variation
The proportion of variation in a trait due to the effects of genetic factors.
Heterotroph
An organism with a requirement for energy-rich organic molecules (animals, fungi and most bacteria).
Heterotrophic succession
A temporal succession of species at a location, principally involving animals.
Heterozygote
An organism carrying different alleles at the corresponding sites on homologous chromosomes.
Hibernate
To remain dormant during the winter period.
Holoparasite
Parasitic plants which lack chlorophyll and are therefore wholly dependent on their host plant for the supply of water, nutrients and fixed carbon.
Homeostasis
Maintenance of relatively constant internal conditions in the face of a varying external environment.
Homeotherm
An organism which maintains an approximately constant body temperature, usually above that of the surrounding medium.
Homing
To return accurately to the place of origin, e.g. the return of salmon, after migration to the sea, to the same river in which they originally hatched.
Homologous structures
Similarity in structure assumed to result from a common ancestry, e.g. the wing of a bird and the foreleg of a mammal.
Homozygote
An organism carrying identical alleles at the corresponding sites on homologous chromosomes.
Host
An organism which is parasitized by a parasite.
Host density dependence
Applied to the aggregation of risk to hosts from parasitoid attacks: hosts in either higher or lower host density patches tend to be at a greater risk of attack (direct and inverse host density dependence, respectively). Could also be applied to other predator - prey interactions. (See also Aggregation of risk and cf. Host density independence.)
Host density independence
Applied to the aggregation of risk to hosts from parasitoid attacks: risk varies from patch to patch but is not related to host density in a patch. Could also be applied to other predator - prey interactions. (See also Aggregation of risk and cf. Host density dependence.)
Hydrological cycle
The movement of water from ocean, by evaporation, to atmosphere, to land and back, via river flow, to ocean.
Hydrophilia
An overwhelming desire for water.
Hydrospheric
Pertaining to the water in soil, river, lake and ocean.

 
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