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Equilibrium number of species (Sequilibrium) is determined by the intersection of the immigration ( I ) and extinction ( E ) rate curves. P is the maximum number of species in the source pool.

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from article Digenea

Diagrams of various adult types of digenean trematodes. (After R. M. Cable, An Illustrated Laboratory Manual of Parasitology, Burgess, Minneapolis, 1940)

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from article Digenea

Digenean trematode life cycle. (After R. M. Cable, An Illustrated Laboratory Manual of Parasitology, Burgess, Minneapolis, 1940)

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from article Learning

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from article Learning

Brain activity can be recorded in various ways, from single-cell activity (top tracing) to the familiar electrical patterns ("brain waves") of an electroencephalogram (bottom tracing). (Credit: Based on an original drawing by C. Cotman and J.…

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from article Biofilm

Biofilms are highly structured communities of microorganisms that are surface-associated or attached to one another, and are enclosed within a self-produced protective extracellular matrix. Biofilm formation and actions involve a number of stages:…

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from article Ctenothrissiformes

A Cretaceous ctenothrissiform fossil, Ctenothrissa sp. (order Ctenothrissiformes), on a limestone matrix found in Lebanon. Size: 90 mm (3.5 in.). (Photo courtesy of The Virtual Fossil Museum)

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from article Acari

Parasitiformes body plan. Lateral view of a predatory adult female Mesostigmata showing major body regions and important structures. Scale bar = 0.1 mm (0.004 in.). (Scanning electron micrograph by D. E. Walter)

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from article Acari

Acariformes body plan. (a) Adult female Oribatida (Sarcoptiformes) in lateral view showing major body regions and important structures. (b) Hexapod larva (Trombidiformes): dorsal view of a chigger, a parasite of vertebrates. (c) Octopod deutonymph…

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from article Ecosystem

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from article Ecosystem

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from article Ecosystem

Food chains are limited by energy transfer. In this illustration, energy is transferred from the Sun to a plant (producer) to a primary consumer and to a secondary consumer. Energy is used by the producer and consumer organisms and is lost to the…

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from article Ecosystem

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from article Ecosystem

General model of the carbon cycle in ecosystems: (A) carbon dioxide (CO2) from the air; (B) carbon from decomposition; (C) carbon from fossil fuels; (D) natural events (for example, forest fires and volcanoes) release CO2 into the air. (Copyright ©…

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from article Biodiversity

Global biodiversity hotspots. There are more than 30 biodiversity hotspots located around the world. These areas have experienced severe habitat losses (at least 70%) as the result of human activities, hampering the work of conservationists in their…

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from article Biodiversity

A regional analysis of 25 oceanic regions shows that 92% of all known biodiversity falls into a dozen groups, of which crustaceans (for example, crabs, shrimps, and lobsters), mollusks (for example, snails, bivalves, squids, and octopus), and fish…

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from article Biodiversity

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from article Haplosporida

Spore of Urosporidium fuliginosum.

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from article Haplosporida

Stages in the development of Icthyosporidium giganteum.

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from article Urodela

A typical member of the order Urodela: the longtail salamander (Eurycea longicauda). (Credit: Ryan Hagerty/U.S. Fish and Wildlife Service)

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from article Urodela

Southern dwarf siren (Pseudobranchus axanthus), which has undergone limb degeneration and retains only tiny forelimbs. (Credit: U.S. Geological Survey)

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from article Urodela

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from article Urodela

California tiger salamander (Ambystoma californiense). (Credit: John Cleckler/U.S. Fish and Wildlife Service)

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from article Urodela

The two-toed amphiuma salamander (Amphiuma means). (Credit: Southeast Ecological Center, U.S. Geological Survey)

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from article Urodela

The northern red salamander (Pseudotriton ruber ruber) is a member of the family Plethodontidae. (Credit: Alicia Lafever/U.S. National Park Service)

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from article Thirst and sodium appetite

Regulation of cellular water. ADH = antidiuretic hormone.

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from article Thirst and sodium appetite

Hypovolemic thirst and sodium appetite are caused by altered sensory information from an underfilled circulation, reinforced by increases in circulating angiotensin II and mineralocorticoids. Angiotensin peptides generated from components of a…

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from article Chamois

Alpine chamois (Rupicapra rupicapra). (Photograph courtesy of Brent Huffman/Ultimate Ungulate Images)

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from article Environmental management

Environmental management seeks to provide solutions to the practical problems that humans encounter or create, including the production of garbage and waste. (Credit: Walter Zerla/Getty Images)

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from article Environmental management

Without proper environmental management, economic and industrial development often lead to environmental pollution, especially in urban environments. (Credit: Simon Alvinge/123RF)

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from article Amniota

Basic types of vertebrate eggs.

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from article Amniota

Embryo developing in amniote eggs.

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from article Mecoptera

Male scorpion fly (Panorpa), order Mecoptera.

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from article Marine ecology

Marine ecology investigates the basic structural and functional relationships within and among living populations and their physical–chemical environments in marine ecosystems. In this photograph, a cold water reef in California is host to a…

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from article Marine ecology

The snaking waterways of a mangrove estuary in northwestern Madagascar. (Credit: Michael Fay/Getty Images/National Geographic RF)

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from article Marine ecology

Estuary salt marshes in the Grand Bay National Estuarine Research Reserve, Mississippi. (Credit: P. R. Hoar/National Oceanic and Atmospheric Administration)

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from article Marine ecology

Coral bleaching in the lagoon of Huahine Island, French Polynesia. Coral bleaching is the response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral…

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from article Swamp, marsh, and bog

Young cypress trees growing out of a swamp located in the Florida Everglades. (Credit: Getty Images)

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from article Hemiptera

Phylogenetic relationships among the extant Hemiptera groups.

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from article Hemiptera

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from article Hemiptera

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from article Hemiptera

Mouthparts and method of feeding of a plant bug.

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from article Hemiptera

Plant pests. (a) A colony of aphids on a rose shoot. (b) The citrus mealybug. (Ohio Agricultural Experiment Station)

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from article Hemiptera

An aphid (dorsal aspect).

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from article Hemiptera

Anterior dorsum of various Auchenorrhyncha: (a) cicada; (b) fulgoroid (apical part of antenna omitted); (c) another species of fulgoroid; (d) cercopid; (e) membracid, anterior view of face and pronotum.

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from article Hemiptera

Membracids on stems: (a) adult; (b) nymphs. (Courtesy of C. H. Hanson)

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from article Hemiptera

Peloridora kuscheli China (Peloridiidae).

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from article Hemiptera

Triatoma pallidipennis (Reduviidae). (Photo by E. S. Ross)

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from article Hemiptera

External anatomy of a typical bug.

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from article Hemiptera

Squash bug. (Photo by Scott Bauer, Agricultural Research Service, U.S. Department of Agriculture)

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from article Hemiptera

Brown marmorated stink bug (Halyomorpha halys): adult (top) and fifth-instar nymph (bottom). (Photo by Stephen Ausmus, Agricultural Research Service, U.S. Department of Agriculture)

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from article Hemiptera

Oblique-dorsal view of a bedbug, Cimex lectularius. (Photo by Piotr Naskrecki, Public Health Image Library)

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from article Hemiptera

Nymph of the tarnished plant bug (Lygus lineolaris). (Photo by Scott Bauer, Agricultural Research Service, U.S. Department of Agriculture)

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from article Obolellida

Obolella. (a) Shell exterior (after J. Hall and J. M. Clarke, An introduction to the study of the Brachiopoda intended as a handbook for the use of students, Report of the N.Y. State Geologist for 1891, 1894). (b) Dorsal valve interior, and (c)…

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from article Albuliformes

Albula vulpes. (Courtesy of C. Q. Jessen)

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from article Mollusca

Higgins eye pearly mussels (Lampsilis higginsii). (Credit: U.S. Fish and Wildlife Service)

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from article Mollusca

Snails are assigned to the class Gastropoda in the phylum Mollusca. (Credit: Zuzha/Shutterstock)

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from article Mollusca

Generalized model of a stem mollusk (or archetype) in side view. There are three distinct regions in the molluscan body: head-foot, visceral mass, and mantle-shell. Water circulation through the mantle cavity, gills (ctenidia), and pallial complex…

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from article Mollusca

Arrangement of the mantle and shell layers in mollusks. The fleshy mantle margin is divided into three lobes, and the outer pallial lobe is largely responsible for secretion of the three layers of the shell. (Credit: W. D. Russell-Hunter)

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from article Mollusca

Aspidobranch ctenidium (feather or plume gill) as found in primitive gastropods and other molluscan groups. (a) Stereogram showing the water current from the ventral inhalant to the dorsal exhalant between adjacent gill plates; this current is…

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from article Mollusca

Common octopus (Octopus vulgaris). (Credit: Aerial-motion/Shutterstock)

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from article Heterotrichida

Climacostomum, an example of a heterotrich.

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from article Paleoecology

Zonation of Silurian (425 million year old) marine communities in the Welsh Basin, United Kingdom. Marine animal communities were typically arranged in belts parallel to the shoreline and related to water depth. A classic study using fossil…

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from article Paleoecology

Classification of shales in terms of percentages of three benthic habitat groups: epifaunal suspension-feeding bivalves (those living at the sediment-water interface and filtering seawater), infaunal (living within and feeding on the sediment), and…

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from article Paleoecology

Comparison of four developmental stages in four ancient reef masses. (After K. R. Walker and L. P. Alberstadt, Ecological succession as an aspect of structure in fossil communities, Paleobiology, 3:238–257, 1975)

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from article Paleoecology

Formation and burial sequence of Bobcaygeon hardground. (a) Soft-bottom community of strophomenid brachiopods and infaunal burrowers inhabiting carbonate mud. (b) Hardground community consisting of boring and encrusting organisms. (c)…

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from article Paleoecology

Tiering or vertical depth stratification in marine communities through time. Note the rapid rise of the highest-tier (level) organisms (crinoids or sea lilies, bryozoans) from a few centimeters to over a meter above the sea floor during the…

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from article Paleoecology

The three great marine evolutionary faunas of the Phanerozoic. The Cambrian fauna, composed of trilobites, primitive groups of brachiopods, and mollusks, arose early during that period to a diversity of about 50 families, and then dwindled during…

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from article Coral reef structural complexity

A fire coral before and after bleaching, which can occur when coral are environmentally stressed. The fire coral on the left is healthy, whereas the one on the right is completely bleached. (Credit: XL Catlin Seaview Survey)

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from article Coral reef structural complexity

Underwater photographs of Cane Bay (St. Croix, U.S. Virgin Islands) in 1980 (left) and 2007 (right). Note the common overgrowth of fleshy macroalgae between the sparsely distributed corals in 2007 compared to the more open substrate in 1980 between…

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from article Coral reef structural complexity

Historical changes related to coral reef decline since the 1600s. The emergence of temperature-related responses (bleaching and disease) is coincident with the loss of urchins (Diadema) and the increase of nutrient loading.

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from article Coral reef structural complexity

Three dominant shallow-water communities in the waters surrounding Easter Island. (Left) Since the 1950s, fleshy algae, such as Sargassum, were the dominant cover, and coral was rare in shallow waters. (Middle) In the 1980s, global climate change…

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from article Seasonal affective disorder

Exposure to bright light via a light-therapy box during winter is an effective treatment for individuals suffering from seasonal affective disorder. (Credit: Getty Images)

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from article Seasonal affective disorder

Individuals suffering from seasonal affective disorder often exhibit a variety of symptoms of depression, including increased sleep length, weight gain, and craving for carbohydrates, as well as sexual and social problems, anxiety, lethargy, and…

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from article Velatida

Abactinal surface of Pteraster tesselatus. (In radially symmetrical animals, the abactinal surface pertains to the surface opposite the side where the mouth is located.)

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from article Velatida

Cross section through an arm of Pteraster tesselatus, showing the supradorsal membrane (SD) and tube feet (TF).

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from article Velatida

Abactinal surface of Solaster endeca.

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from article Volvocida

Carteria, showing equal plural flagella.

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from article Volvocida

Morphological features of Volvox. (a) Volvox globator, sectional view; (b) surface view of a single zooid. (c) Volvox aureus, sectional view; (d) sperm, enlarged about eight times by comparison with c.

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from article Respiratory pigments (invertebrate)

Electron micrograph of hemocyanin molecules from the snail Helix pomatia, showing “pillbox” subunit structure. Circular forms show subunits in a tenfold symmetrical array. There are six parallel rows of subunits in the rectangular forms.

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from article Gasterosteiformes

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from article Reptilia

Desert tortoise (Gopherus agassizii). (Credit: Robb Hannawacker/National Park Service)

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from article Reptilia

Western or variable ground snake (Sonora semiannulata). (Credit: Peter Paplanus)

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from article Reptilia

Greater short-horned lizard (Phrynosoma hernandesi). (Credit: Lake Mead National Recreation Area, Arizona–Nevada/National Park Service)

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from article Pegasidae

Short (little) dragonfish (Eurypegasus draconis) found in the waters off the Tayandu Islands, Indonesia. (Photo by Teddy Triandiza)

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from article Rotifera

Common species from the three rotifer groups. (a) The seisonid Seison nebaliae. (b) The bdelloid Philodina roseola. (c) The monogonont Brachionus plicatilis.

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from article Rotifera

Four of the 8 or 9 recognized types of rotifer mastax. (a) Forcipate mastax of the monogonont Albertia vermiculus has all parts of the mallei and incus. (b) Incudate mastax of the monogonont Asplanchna brightwellii has enlarged, pincerlike rami and…

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from article Rotifera

Life cycles of the three rotifer groups. (a) Gonochoristic reproduction in seisonids. (b) Parthenogenesis alternating with sexual reproduction in monogononts. (c) Obligate parthenogenesis in bdelloids. 2n represents diploidy, and n represents…

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from article Calcarea

A calcareous sponge belonging to the family Leucettidae (order Clathrinida). (Credit: Bernard Dupont)

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from article Calcarea

Grades of construction of the water-current system in Calcarea: (a) asconoid type; (b) syconoid type without cortex; (c) syconoid type with cortex; (d) intermediate or transitional stage between syconoid and leuconoid types; (e) leuconoid type.…

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from article Calcarea

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from article Perception

Perception encompasses recognition in response to sensory stimuli. Stimulation of the body's receptor organs is transformed into neural activity and is relayed to more central regions of the nervous system. Then, further neural processing occurs,…

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from article Perception

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from article Perception

Perceptual organization. (a) The figure of a four (4) is immediately and spontaneously perceived, despite the presence of other overlapping and adjacent lines. (b) The four, although physically present, is not spontaneously perceived and is even…

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from article Perception

Transposition of form; the two shapes look the same despite the difference in size.

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from article Perception

This figure is not recognizable. If, however, it is tilted 90° clockwise, it will be recognized as an outline map of Africa.

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from article Perception

Geometrical illusions. (a) The Ponzo illusion in which the two horizontal lines of equal length appear unequal. (b) The Poggendorff illusion in which the two oblique line segments are aligned with one another (that is, are collinear), but appear to…

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from article Sarcomastigophora