Glossary: D


Relating to seasonal loss of leaves; relating to teeth that are replaced by others.

deciduous forest

A temperate or tropical forest with moderate rainfall and marked seasons. The trees usually shed their leaves during either cold or dry seasons.


An animal or microbe that uses dead plants and animals as food.

defensive chemicals

chemicals employed by organisms to prevent predation either by making them distasteful, toxic, or otherwise harmful.

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.


Relating to the statistical study of the age and sex distribution and size of a population of animals, and the changes within these parameters.


A shelter, natural or constructed, used for sleeping, for giving birth and raising young, and/or for providing shelter during winter.

density dependence

The phenomenon by which the values of vital rates such as survivorship and fecundity depend on the density of the population.

deposit feeder

eating small particles of organic material by consuming inorganic sediments and soils


referring to the form a characteristic takes after having undergone a transformative process, e.g. a new form is derived from an ancestral form through evolutionary change. In cladistics, derived characters are referred to as apomorphies.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.


the process of drying up


an animal that mainly eats decomposed plants and/or animals


particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).


referring to the group of higher phyla, the Deuterostomia, in which cleavage of the egg is indeterminate and primitively radial. The endomesoderm is enterocoelus and the mouth is derived away from the blastopore. This group includes Echinodermata, Chordata, Phoronida, Ectoprocta, Brachiopoda, Chaetognatha, and Hemichordata. Compare with protostome (Protostomia).

development determinate

The blastomeres in the embryo each have a predetermined fate which is not altered during development. Synapomorphy of Protostomia.

development regulative

The fate of blastomeres is initially flexible and determined gradually over the course of development; individual blastomeres can follow a different developmental program if repositioned. Synapomorphy of the Deuterostomia.


Referring to fish that must migrate between fresh and salt at some point in their life cycle.


a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.

diapsid skull

The skull has two pairs of temporal openings, one dorsal and one lateral. Synapomorphy of the Diapsida.


One of the classes of flowering plants, characterized by the presence of two seed leaves in the young plant, and by net-veined, often broad leaves, in mature plants. Includes deciduous trees.


A finger or toe.


Relating to an animal that walks on its toes; as opposed to plantigrade.


The occurrence of two distinct forms of structure, size, coloring, or other characteristic in a single species. Sexual dimorphism occurs where dimorphism exists between males and females.


a group of unicellular aquatic organisms with two flagellae. They are variously classified as protozoan or as an algae.


the condition in which individuals are either male or female, male and female gonads do not co-occur in the same individual.


Having deciduous, or non-permanent teeth that are replaced by permanent teeth once during the animal's lifespan (instead of continual tooth replacement, as found in more primitive amniotes). Synapomorphy of the Mammalia.


having a body made up of two layers, the epidermis and gastrodermis, with mesoglea between them, as in cnidarians.

direct development

a pattern of development from egg to adult where the intermediate forms resemble the adult, morphologicallly and ecologically. Examples are amphibians which do not go through a larval stage and many other vertebrates.


shaped flat and round like a disc


Movement of an animal away from its previous home range. Often refers to the movement of a young animal away from the home range where it was born.


Any conspicuous pattern of behavior that conveys information to others, usually to members of the same species; e.g. threat or courtship displays.


Farthest from the body.

distraction display

any display that distracts a predator from an essential body part or from another organisms, such as offspring. Examples are broken-wing displays in order to draw predators away from young or displays that draw attention to peripheral appendages to minimize damage.

  1. active during the day, 2. lasting for one day.
diversity - alpha

The number of species coexisting within a uniform habitat or a single community (this is the traditional concept of species diversity).

diversity - beta

As habitats change along a topographic or climatic gradient, new species are encountered as other species drop out, and this species turnover rate is termed beta diversity - a function of changing habitat. An example would be the rate at which the species composition of moss communities changes as you go higher on a mountain slope.

diversity - gamma

The rate at which additional species are encountered as geographic replacements within a habitat type in different localities; i.e., the species turnover rate with distance between sites of similar habitat, or with expanding geographic areas.


more generally, a sac-like enlargement of any tubular or hollow organ. Generally refers to a pouch in the wall of the alimentary tract caused by pressure on a weak point.

divided circulation

Four chambered heart keeps oxygenated and oxygen-depleted blood flowing separately within the heart. Synapomorphy of the mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds, crocodiles, and possibly dinosaurs.

doliolara larva

used to describe the larvae of crinoids (sea lilies and feather stars), Class Crinoidea, Phylum Echinodermata.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates


a state in which metabolic activities are decreased, including hibernation, aestivation, torpor, and diapause.


On the upper or top side or surface; e.g. dorsal fin.


a term used to describe the position of a body structure or characteristic. Something which is dorsoventrally oriented extends from the back (dorsal side) to the front (ventral side).


a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease


to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate