biology in focus - chapter 27

CAMPBELL BIOLOGY IN FOCUS

Urry • Cain • Wasserman • Minorsky • Jackson • Reece

Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge

27The Rise of Animal Diversity

Overview: Life Becomes Dangerous

Most animals are mobile and use traits such as strength, speed, toxins, or camouflage to detect, capture, and eat other organisms For example, the chameleon captures insect prey with

its long, sticky, fast-moving tongue

Figure 27.1

Current evidence indicates that animals evolved from single-celled eukaryotes similar to present-day choanoflagellates

More than 1.3 million animal species have been named to date; the actual number of species is estimated to be nearly 8 million

Concept 27.1: Animals originated more than 700 million years ago

Fossil and Molecular Evidence

Fossil biochemical evidence and molecular clock studies date the common ancestor of all living animals to the period between 700 and 770 million years ago

Early members of the animal fossil record include the Ediacaran biota, which dates from about 560 million years ago

Figure 27.2

(a) Dickinsoniacostata(taxonomic affiliationunknown)

2.5 cm

(b) The fossilmolluscKimberella

Figure 27.2a

(a) Dickinsoniacostata(taxonomic affiliationunknown)

2.5 cm

Figure 27.2b

(b) The fossilmolluscKimberella

Early-Diverging Animal Groups

Sponges and cnidarians are two early-diverging groups of animals

Figure 27.UN01

Other animalgroups

SpongesCnidarians

Animals in the phylum Porifera are known informally as sponges

Sponges are filter feeders, capturing food particles suspended in the water that passes through their body

Water is drawn through pores into a central cavity and out through an opening at the top

Sponges lack true tissues, groups of cells that function as a unit

Sponges

Figure 27.3

Waterflow

Choanocyte

Flagellum

Food particlesin mucus

CollarChoanocyte

Phagocytosis offood particles

Amoebocyte

Amoebocytes

Azure vase sponge(Callyspongia plicifera)

Spicules

Figure 27.3a

Azure vase sponge(Callyspongia plicifera)

Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended food

Morphological similarities between choanocytes and choanoflagellates are consistent with the hypothesis that animals evolved from a choanoflagellate-like ancestor

Amoebocytes are mobile cells that play roles in digestion and structure

Like most animals, members of the phylum Cnidaria have true tissues

Cnidarians are one of the oldest groups of animals, dating back to 680 million years ago

Cnidarians have diversified into a wide range of both sessile and motile forms, including hydrozoans, jellies, and sea anemones

Cnidarians

Video: Clownfish Anemone

Video: Coral Reef

Video: Hydra Budding

Video: Hydra Eating

Video: Jelly Swimming

Video: Thimble Jellies

Figure 27.4

(c) Anthozoa(a) Hydrozoa (b) Scyphozoa

Figure 27.4a

(a) Hydrozoa

Figure 27.4b

(b) Scyphozoa

Figure 27.4c

(c) Anthozoa

The basic body plan of a cnidarian is a sac with a central digestive compartment, the gastrovascular cavity

A single opening functions as mouth and anus Cnidarians are carnivores that use tentacles to

capture prey Cnidarians have no brain, but instead have a

noncentralized nerve net associated with sensory structures distributed throughout the body

Concept 27.2: The diversity of large animals increased dramatically during the “Cambrian explosion”

The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals

Strata formed during the Cambrian explosion contain the oldest fossils of about half of all extant animal phyla

Evolutionary Change in the Cambrian Explosion

Figure 27.5

Echinoderms

Sponges

Cnidarians

Chordates

Brachiopods

Annelids

Molluscs

Ediacaran

Arthropods

635CambrianPALEOZOICPROTEROZOIC

605Time (millions of years age)

575 545 515 485 0

Fossils from the Cambrian period include the first hard, mineralized skeletons

Most fossils from this period are of bilaterians, a clade whose members have a complete digestive tract and a bilaterally symmetric form

Figure 27.6

Hallucigenia fossil(530 mya)

Figure 27.6a

Figure 27.6b

Hallucigenia fossil(530 mya)

There are several hypotheses regarding the cause of the Cambrian explosion and decline of Ediacaran biota New predator-prey relationships A rise in atmospheric oxygen The evolution of the Hox gene complex

Dating the Origin of Bilaterians

Molecular clock estimates date the bilaterians to 100 million years earlier than the oldest fossil, which lived 560 million years ago

The appearance of larger, well-defended eukaryotes 635–542 million years ago indicates that bilaterian predators may have originated by that time

Figure 27.7

(a) Valeria (800 mya):roughly spherical, nostructural defenses,soft-bodied

(b) Spiny acritarch(575 mya): about fivetimes larger thanValeria and covered inhard spines

Figure 27.7a

(a) Valeria (800 mya):roughly spherical, nostructural defenses,soft-bodied

Figure 27.7b

(b) Spiny acritarch(575 mya): about fivetimes larger thanValeria and covered inhard spines

Concept 27.3: Diverse animal groups radiated in aquatic environments

Animals in the early Cambrian oceans were very diverse in morphology, way of life, and taxonomic affiliation

Animal Body Plans

Zoologists sometimes categorize animals according to a body plan, a set of morphological and developmental traits

There are three important aspects of animal body plans Symmetry Tissues Body cavities

Symmetry

Animals can be categorized according to the symmetry of their bodies or lack of it

Some animals have radial symmetry, with no front and back or left and right

Figure 27.8

(b) Bilateral symmetry

(a) Radial symmetry

Two-sided symmetry is called bilateral symmetry Bilaterally symmetrical animals have

A dorsal (top) side and a ventral (bottom) side A right and left side Anterior (head) and posterior (tail) ends

Many also have sensory equipment concentrated in the anterior end, including a brain in the head

Radial animals are often sessile or planktonic (drifting or weakly swimming)

Bilateral animals often move actively and have a central nervous system enabling coordinated movement

Tissues

Animal body plans also vary according to the organization of the animal’s tissues

Tissues are collections of specialized cells isolated from other tissues by membranous layers

During development, three germ layers give rise to the tissues and organs of the animal embryo

Figure 27.9

Digestive tract(from endoderm)

Body covering(from ectoderm)

Tissue layerlining body cavityand suspendinginternal organs(from mesoderm)

Body cavity

Ectoderm is the germ layer covering the embryo’s surface

Endoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron

Cnidarians have only these two germ layers Mesoderm is a third germ layer that fills the space

between the ectoderm and the endoderm in all bilaterally symmetric animals

Body Cavities

Most bilaterians possess a body cavity (coelom), a fluid- or air-filled space between the digestive tract and the outer body wall

The body cavity may Cushion suspended organs Act as a hydrostatic skeleton Enable internal organs to move independently of the

body wall

The Diversification of Animals

Zoologists recognize about three dozen animal phyla

Phylogenies now combine molecular data from multiple sources with morphological data to determine the relationships among animal phyla

Video: C. Elegans Crawling

Video: Earthworm Locomotion

Video: Echinoderm Tubefeet

Video: Nudibranchs

Video: Rotifer

Figure 27.10

ANCESTRALPROTIST

770 millionyears ago

Arthropoda

Nematoda

Annelida

Mollusca

Brachiopoda

Ectoprocta

Rotifera

Platyhelminthes

Chordata

Echinodermata

Metazoa

Hemichordata

Cnidaria

Ctenophora

Porifera

EcdysozoaLophotrochozoa

Bilateria

Deuterostom

Eumetazoa

The following points are reflected in the animal phylogeny

1. All animals share a common ancestor2. Sponges are basal animals3. Eumetazoa is a clade of animals (eumetazoans) with

true tissues4. Most animal phyla belong to the clade Bilateria and are

called bilaterians5. Most animals are invertebrates, lacking a backbone;

Chordata is the only phylum that includes vertebrates, animals with a backbone

Bilaterian Radiation I: Diverse Invertebrates

Bilaterians have diversified into three major clades Lophotrochozoa Ecdysozoa Deuterostomia

An Overview of Invertebrate Diversity

Bilaterian invertebrates account for 95% of known animal species

They are morphologically diverse and occupy almost every habitat on Earth

This morphological diversity is mirrored by extensive taxonomic diversity

The vast majority of invertebrate species belong to the Lophotrochozoa and Ecdysozoa; a few belong to the Deuterostomia

Figure 27.11

Arthropoda(1,000,000 species)

Nematoda(25,000 species)

Annelida (16,500 species)

Mollusca(93,000 species)

Ectoprocta(4,500 species)

Ectoprocts

EcdysozoaLophotrochozoa

Echinodermata(7,000 species)

Hemichordata(85 species)

Deuterostomia

An octopus A roundworm

A web-building spider(an arachnid)

Sea urchins and asea starAn acorn worm

A fireworm, a marine annelid

Figure 27.11a

Ectoprocts

Lophotrochozoa

An octopus

Figure 27.11aa

Ectoprocts

Figure 27.11ab

An octopus

Figure 27.11ac

Figure 27.11b

Ecdysozoa

A roundworm

Figure 27.11ba

A roundworm

Figure 27.11bb

Figure 27.11c

Echinodermata(7,000 species

Deuterostomia

Sea urchins and asea starAn acorn worm

Figure 27.11ca

An acorn worm

Figure 27.11cb

Echinodermata(7,000 species)

Sea urchins and asea star

Arthropod Origins

Two out of every three known species of animals are arthropods

Members of the phylum Arthropoda are found in nearly all habitats of the biosphere

The arthropod body plan consists of a segmented body, hard exoskeleton, and jointed appendages

This body plan dates to the Cambrian explosion (535–525 million years ago)

Early arthropods show little variation from segment to segment

Figure 27.UN02

A fossil trilobite

Arthropod evolution is characterized by a decrease in the number of segments and an increase in appendage specialization

These changes may have been caused by changes in Hox gene sequence or regulation

Figure 27.12

Red indicates regionsin which Ubx orabd-A genes wereexpressed.

Otherecdysozoans

Arthropods

OnychophoransCommon ancestor

Origin of Ubx andabd-A Hox genes?

Ant antennaJ jawsL1–L15 body segments

Experiment

Results

Figure 27.12a

Red indicates regionsin which Ubx orabd-A genes wereexpressed.

Ant antennaJ jawsL1–L15 body segments

Results

Bilaterian Radiation II: Aquatic Vertebrates

The appearance of large predatory animals and the explosive radiation of bilaterian invertebrates radically altered life in the oceans

One type of animal gave rise to vertebrates, one of the most successful groups of animals

Figure 27.13

The animals called vertebrates get their name from vertebrae, the series of bones that make up the backbone

Vertebrates are members of phylum Chordata Chordates are bilaterian animals that belong to the

clade of animals known as Deuterostomia

Early Chordate Evolution

All chordates share a set of derived characters Some species have some of these traits only during

embryonic development Four key characters of chordates

Notochord, a flexible rod providing support Dorsal, hollow nerve cord Pharyngeal slits or pharyngeal clefts, which function

in filter feeding, as gills, or as parts of the head Muscular, post-anal tail

Video: Clownfish Anemone

Video: Coral Reef

Video: Manta Ray

Video: Sea Horses

Figure 27.14

Musclesegments

Notochord

Post-anal tail

Dorsal, hollow nerve cord

Pharyngeal slits or clefts

Lancelets are a basal group of extant, blade-shaped animals that closely resemble the idealized chordate

Tunicates are another early diverging chordate group, but they only display key chordate traits during their larval stage

The ancestral chordate may have looked similar to a lancelet

Figure 27.15

(a) Lancelet (b) Tunicate

Figure 27.15a

(a) Lancelet

Figure 27.15b

(b) Tunicate

In addition to the features of all chordates, early vertebrates had a backbone and a well-defined head with sensory organs and a skull

Fossils representing the transition to vertebrates formed during the Cambrian explosion

The Rise of Vertebrates

Early vertebrates were more efficient at capturing food and evading predators than their ancestors

The earliest vertebrates were conodonts, soft-bodied, jawless animals that hunted prey using a set of barbed hooks in their mouth

There are only two extant lineages of jawless vertebrates, the hagfishes and lampreys

Figure 27.16

Chondrichthyes ActinistiaActinopterygii

Myxini

Tetrapoda

Petromyzontida

Dipnoi

Chondrichthyes(sharks, rays, chimaeras)

Actinistia(coelacanths)

Actinopterygii(ray-finned fishes)

Myxini(hagfishes)

Tetrapoda(amphibians,reptiles,mammals)

Petromyzontida(lampreys)

Dipnoi(lungfishes)

Limbs with digits

Lobedfins

Lungsor lung derivatives

Jaws,mineralized

skeleton

Vertebralcolumn

Commonancestor ofvertebrates

TetrapodsLobe-fins

Osteichthyans

Gnathostom

esVertebrates

Figure 27.16a

Chondrichthyes(sharks, rays, chimaeras)

Actinistia(coelacanths)

Actinopterygii(ray-finned fishes)

Myxini(hagfishes)

Tetrapoda(amphibians,reptiles,mammals)

Petromyzontida(lampreys)

Dipnoi(lungfishes)

Limbs with digits

Lobedfins

Lungsor lung derivatives

Jaws,mineralized

skeleton

Vertebralcolumn

Commonancestor ofvertebrates

Tetrapods

Lobe-finsO

steichthyansG

nathostomes

Vertebrates

Figure 27.16b

Chondrichthyes

ActinistiaActinopterygiiMyxini

Tetrapoda

Petromyzontida

Dipnoi

Figure 27.16ba

Myxini

Figure 27.16bb

Petromyzontida

Figure 27.16bba

Figure 27.16bbb

Figure 27.16bc

Chondrichthyes

Figure 27.16bd

Actinopterygii

Figure 27.16be

Actinistia

Figure 27.16bf

Dipnoi

Figure 27.16bg

Tetrapoda

Today, jawed vertebrates, or gnathostomes, outnumber jawless vertebrates

Early gnathostome success is likely due to adaptations for predation including paired fins and tails for efficient swimming and jaws for grasping prey

Video: Lobster Mouth Parts

Figure 27.17

Gnathostomes diverged into three surviving lineages, chondrichthyans, ray-finned fishes, and lobe-fins

Humans and other terrestrial animals are included in the lobe-fins

Chondrichthyans include sharks, rays, and their relatives

The skeletons of chondrichthyans are composed primarily of cartilage

This group includes some of the largest and most successful vertebrate predators

Ray-finned fishes include nearly all the familiar aquatic osteichthyans

The vast majority of vertebrates belong to the clade of gnathostomes called Osteichthyes

Nearly all living osteichthyans have a bony endoskeleton

Lobe-fins are the other major lineage of osteichthyans

A key derived trait in the lobe-fins is the presence of rod-shaped bones surrounded by a thick layer of muscle in their pectoral and pelvic fins

Three lineages survive: the coelacanths, lungfishes, and tetrapods, terrestrial vertebrates with limbs and digits

Concept 27.4: Several animal groups had features facilitating their colonization of land

Some bilaterian animals colonized land following the Cambrian explosion, causing profound changes in terrestrial communities

Early Land Animals

Members of many animal groups made the transition to terrestrial life

Arthropods were among the first animals to colonize the land about 450 million years ago

Vertebrates colonized land 365 million years ago

The evolutionary changes that accompanied the transition to terrestrial life were much less extensive in animals than in plants

Video: Bee Pollinating

Video: Butterfly Emerging

Figure 27.18

GREEN ALGA MARINE CRUSTACEAN AQUATIC LOBE-FIN

Derived (roots) N/A N/A

LAND PLANTS INSECTS TERRESTRIALVERTEBRATES

Derived (lignin/stems)

Derived (vascular system)

Derived (cuticle)

Derived (stomata) Derived (tracheal system)

Ancestral

Derived(amniotic egg/scales)

Ancestral

Ancestral (skeletal system)Derived (limbs)

Ancestral

Anchoringstructure

Supportstructure

Internaltransport

Muscle/nerve cells

Protectionagainst

desiccation

Gas exchange

Figure 27.18a

GREEN ALGA

Derived (roots)

LAND PLANTS

Derived (lignin/stems)

Derived (vascular system)

Derived (cuticle)

Derived (stomata)

Anchoring structure

Support structure

Internal transport

Muscle/nerve cellsProtection against

desiccationGas exchange

Figure 27.18b

Anchoring structure

Support structure

Internal transport

Muscle/nerve cellsProtection against

MARINE CRUSTACEAN

INSECTS

Derived (tracheal system)

Ancestral

Figure 27.18c

Anchoring structure

Support structure

Internal transportMuscle/nerve cellsProtection against

AQUATIC LOBE-FIN

TERRESTRIALVERTEBRATES

Derived(amniotic egg/scales)

AncestralAncestral

Ancestral (skeletal system)Derived (limbs)

Ancestral

Colonization of Land by Arthropods

Terrestrial lineages have arisen in several different arthropod groups, including millipedes, spiders, crabs, and insects

General Characteristics of Arthropods

The appendages of some living arthropods are modified for functions such as walking, feeding, sensory reception, reproduction, and defense

Figure 27.19

Cephalothorax

Swimming appen-dages (one pair perabdominal segment)

Abdomen

Antennae(sensoryreception)

ThoraxHead

Pincer(defense)

Mouthparts(feeding)

Walking legs

The body of an arthropod is completely covered by the cuticle, an exoskeleton made of layers of protein and the polysaccharide chitin

The exoskeleton provides structural support and protection from physical harm and desiccation

A variety of organs specialized for gas exchange have evolved in arthropods

Insects

The insects and their relatives include more species than all other forms of life combined

They live in almost every terrestrial habitat and in fresh water

Figure 27.20

Lepidopterans

Hymenopterans Hemipterans

Figure 27.20a

Lepidopterans

Figure 27.20aa

Figure 27.20ab

Figure 27.20b

Hymenopterans

Figure 27.20c

Hemipterans

Insects diversified several times following the evolution of flight, adaptation to feeding on gymnosperms, and the expansion of angiosperms

Insect and plant diversity declined during the Cretaceous extinction, but has been increasing in the 65 million years since

Flight is one key to the great success of insects An animal that can fly can escape predators, find

food, and disperse to new habitats much faster than organisms that can only crawl

Figure 27.21

Terrestrial Vertebrates

One of the most significant events in vertebrate history was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods

The Origin of Tetrapods

Tiktaalik, nicknamed a “fishapod,” shows both fish and tetrapod characteristics

It had Fins, gills, lungs, and scales Ribs to breathe air and support its body A neck and shoulders Fins with the bone pattern of a tetrapod limb

Figure 27.22

FishCharacters

Neck Shoulder bones

Ulna Flat skull

Eyes on top of skull

Humerus

Ribs Scales

Fin skeleton

Elbow Radius

“Wrist”

TetrapodCharacters

ScalesFinsGills and lungs

NeckRibsFin skeletonFlat skullEyes on top of skull

Figure 27.22a

Neck Shoulder bones

Flat skull

Eyes on top of skull

Figure 27.22b

Figure 27.22c

Scales

Figure 27.22d

Ulna Humerus

Fin skeleton

Elbow Radius

“Wrist”

Tiktaalik could most likely prop itself on its fins, but not walk

Fins became progressively more limb-like over evolutionary time, leading to the first appearance of tetrapods 365 million years ago

Figure 27.23

Lungfishes

Eusthenopteron

Panderichthys

Tiktaalik

Acanthostega

Tulerpeton

Amphibians

Amniotes

Limbswith digits

Silurian Permian Carboniferous Devonian

PALEOZOIC

Key tolimb bones

Time (millions of years ago) 415 340 355 370 385 400 325 280 295 310 265 0

UlnaRadiusHumerus

Figure 27.23a

PALEOZOIC

Key tolimb bones

UlnaRadiusHumerus

Lungfishes

Eusthenopteron

Panderichthys

Tiktaalik

Lobe-fins with limbs with digits

Figure 27.23b

PALEOZOIC

Key tolimb bones

UlnaRadiusHumerus

Acanthostega

Tulerpeton

Amphibians

Amniotes

Limbswith digits

Amphibians

Amphibians are represented by about 6,150 species including salamanders, frogs, and caecilians

Amphibians are restricted to moist areas within their terrestrial habitats

Video: Marine Iguana

Video: Flapping Geese

Video: Snake Wrestling

Video: Soaring Hawk

Video: Swans Taking Flight

Video: Tortoise

Figure 27.24

Salamandersretain their tailsas adults.

Caecilians haveno legs and aremainly burrowinganimals.

Frogs and toadslack tails as adults.

Figure 27.24a

Salamanders retain their tails asadults.

Figure 27.24b

Frogs and toads lack tails as adults.

Figure 27.24c

Caecilians have no legs and aremainly burrowing animals.

Terrestrial Adaptations in Amniotes

Amniotes are a group of tetrapods whose living members are the reptiles, including birds, and mammals

Amniotes are named for the major derived character of the clade, the amniotic egg, which contains membranes that protect the embryo

The extraembryonic membranes are the amnion, chorion, yolk sac, and allantois

The amniotic eggs of most reptiles and some mammals have a shell

Video: Bat Licking

Video: Bat Pollinating

Video: Chimp Agonistic

Video: Chimp Cracking Nut

Video: Gibbon Brachiating

Video: Sea Lion

Video: Shark Eating Seal

Video: Wolves Agonistic

Figure 27.25

Amnioticcavity withamniotic fluid Yolk

(nutrients)

Albumen

Yolk sac

ChorionAllantoisAmnion

Embryo

Extraembryonic membranes

The Origin and Radiation of Amniotes

Living amphibians and amniotes split from a common ancestor about 350 million years ago

Early amniotes were more tolerant of dry conditions than early tetrapods

The earliest amniotes were small predators with sharp teeth and long jaws

Reptiles are one of two living lineages of amniotes Members of the reptile clade includes the tuataras,

lizards, snakes, turtles, crocodilians, birds, and some extinct groups

Figure 27.26

Tuataras

Squamates

Crocodilians

Turtles

†Plesiosaurs

†Pterosaurs

†Ornithischiandinosaurs

†Saurischiandinosaurs otherthan birds

Crocodilians

Turtles

Tuataras

Squamates

Commonancestorof dinosaurs

Commonancestorof reptiles

Figure 27.26a

†Plesiosaurs

†Pterosaurs

†Ornithischiandinosaurs

†Saurischiandinosaurs otherthan birds

Crocodilians

Turtles

Tuataras

Squamates

Commonancestorof dinosaurs

Commonancestorof reptiles

Figure 27.26b

Tuataras Squamates

Crocodilians

Turtles

Figure 27.26ba

Crocodilians

Figure 27.26bb

Figure 27.26bba

Figure 27.26bbb

Figure 27.26bc

Turtles

Figure 27.26bd

Tuataras

Figure 27.26be

Squamates

Reptiles have scales that create a waterproof barrier Most reptiles lay shelled eggs on land Most reptiles are ectothermic, absorbing external

heat as the main source of body heat Birds are endothermic, capable of keeping the body

warm through metabolism

Mammals are the other extant lineage of amniotes There are many distinctive traits of mammals

including Mammary glands that produce milk Hair A fat layer under the skin A high metabolic rate, due to endothermy Differentiated teeth

The first true mammals evolved from synapsids and arose about 180 million years ago

By 140 million years ago, the three living lineages of mammals had emerged Monotremes, egg-laying mammals Marsupials, mammals with a pouch Eutherians, placental mammals

Figure 27.27

Monotremes Marsupials

Eutherians

Figure 27.27a

Monotremes

Figure 27.27aa

Figure 27.27ab

Figure 27.27b

Marsupials

Figure 27.27c

Eutherians

Human Evolution

Humans (Homo sapiens) are primates, nested within a group informally called apes

Figure 27.28

New World monkeys

Old World monkeys

Humans

Chimpanzeesand bonobos

Gorillas

Orangutans

Gibbons

“Apes”

A number of characters distinguish humans from other apes Upright posture and bipedal locomotion Larger brains capable of language, symbolic thought,

artistic expression, and the use of complex tools

The evolution of bipedalism preceded the evolution of increased brain size in early human ancestors

Brain size, body size, and tool use increased over time in Homo species

Modern humans, H. sapiens, originated in Africa about 200,000 years ago and colonized the rest of the world from there

Figure 27.29

Concept 27.5: Animals have transformed ecosystems and altered the course of evolution

The rise of animals from a microbe-only world affected all aspects of ecological communities, in the sea and on land

Ecological Effects of Animals

The oceans of early Earth likely had very different properties than the oceans of today

Figure 27.30

(b) Changes to ocean conditions by 530 mya

(a) Ocean conditions before 600 mya

Murky, poorly-mixedLow oxygenCyanobacteria

Clear, well-mixedHigh oxygenEukaryotic algae

Marine Ecosystems

The rise of filter-feeding animals likely caused the decline of cyanobacteria and other suspended particles in the oceans during the early Cambrian

This resulted in a shift to algae as the dominant producers and changed the feeding relationships in marine ecosystems

Terrestrial ecosystems were transformed with the move of animals to land

Herbivores, such as the lesser snow goose, can improve the growth of plants at low population sizes through additions of nutrient-rich wastes

At high population sizes herbivores can defoliate large tracts of land

Terrestrial Ecosystems

Figure 27.31

Evolutionary Effects of Animals

The origin of mobile, heterotrophic animals with a complete digestive tract drove some species to extinction and initiated ongoing “arms races” between bilaterian predators and prey

Evolutionary Radiations

Two species that interact can exert strong, reciprocal selective pressures on one another For example, flower form can be influenced by the

structure of its pollinators’ mouth parts, and vice versa

Figure 27.32

Reciprocal selection pressures can also occur when the origin of new species in one group stimulates further radiation in another group For example, the origin of a new group of

animals provides new food sources for parasites, resulting in radiations in parasite groups

Human Impacts on Evolution

Humans have made large changes to the environment that have altered the selective pressures faced by many species For example, human targeting of large fish for

harvesting has led to the reduction in age and size at which individuals reach sexual maturity

Figure 27.33

1960 1970 1980 1990 2000Year

ity (y

Figure 27.33a

Rapid species declines over the past 400 years indicate that human activities may be driving a sixth mass extinction

Molluscs, including pearl mussels, have suffered the greatest impact of human-caused extinctions

Figure 27.34

Workers on a mound of pearlmussels killed to make buttons(ca. 1919)

An endangeredPacific islandland snail,Partula suturalis

Recorded extinctions of animalspecies

Otherinvertebrates

Reptiles (excludingbirds)

Molluscs

Insects

Fishes Birds

Mammals

Amphibians

Figure 27.34a

Recorded extinctions of animal species

Otherinvertebrates

Reptiles (excludingbirds)

Molluscs

Insects

Fishes Birds

Mammals

Amphibians

Figure 27.34b

An endangeredPacific islandland snail,Partula suturalis

Figure 27.43c

Workers on a mound of pearlmussels killed to make buttons(ca. 1919)

The major threats imposed on species by human activities include habitat loss, pollution, and competition or predation by introduced, non-native species

Figure 27.UN03

SouthernperiwinklesNorthernperiwinkles

Southern Northern

Source population of crab

Figure 27.UN04

Origin anddiversification

of dinosaurs365 mya:Early land

animalsDiversification

of mammals

535–525 mya:Cambrian explosion

560 mya:Ediacaran animals

Millions of years age (mya)

Neo-proterozoic Paleozoic

542 251

Mesozoic

Ceno- zoic

Figure 27.UN05

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biology in focus - chapter 36

biology in focus - chapter 18

biology in focus - chapter 24

biology in focus - chapter 37

biology in focus - chapter 35

06 biology special focus evolution

biology in focus chapter 4

biology in focus - chapter 20

biology in focus - chapter 28

biology in focus - chapter 11

biology in focus chapter 1

biology in focus - chapter 34

biology in focus - chapter 38

biology in focus - chapter 7

biology in focus - chapter 23

biology in focus - chapter 17