Avian biogeography CHAPTER 2. Why study biogeography of birds ? Different aspects of avian biology...
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Avian biogeography CHAPTER 2. Why study biogeography of birds ? Different aspects of avian biology addressed how have new bird species arisen ? how did
Why study biogeography of birds ? Different aspects of avian
biology addressed how have new bird species arisen ? how did they
come to be distributed in the way they are ? how are patterns of
distribution and diversity maintained ? how does their
(behavioural) ecology differ between regions ?
Slide 3
Why study biogeography of birds ? Birds as ecological model
evolutionary relationships well understood
Slide 4
Why study biogeography of birds ? Birds as ecological
model
Slide 5
Why study biogeography of birds ? Birds as ecological model
Irwin et al. 2001. Speciation in a ring. Nature 409: 333-337
Slide 6
Why study biogeography of birds ? Birds as ecological model
evolutionary relationships well understood geographical pattern of
morphological variation well studied distributional patterns well
mapped
Slide 7
Why study biogeography of birds ? Birds as ecological model
Opisthocomus hoazin
Slide 8
Why study biogeography of birds ? Birds as ecological model
evolutionary relationships well understood geographical pattern of
morphological variation well studied distributional patterns well
mapped high mobility allows presence and radiation on remote
islands very strong seasonal migration large-scale ringing
data
Slide 9
Continental birds
Slide 10
level of distinctiveness of land-masses reflects both their
relative position and geological history (tectonics, duration and
degree of isolation, opportunities for separate evolution)
Slide 11
Continental birds Geological time scale and break-up of
Gondwanaland Archaeopteryx ca 150
Slide 12
Continental birds level of distinctiveness of land-masses
reflects both their relative position and geological history
(tectonics, duration and degree of isolation, opportunities for
separate evolution) combination of present distribution patterns
along with palaeo- geological evidence 19th century: global system
first developed for passerine birds, then modified by Alfred Russel
Wallace (1876) to apply to animals in general crucial barriers are
seas, deserts, mountain ranges, climatic- vegetation ecotones
Slide 13
Continental birds Main biogeographical regions of the
world
Slide 14
Continental birds Main biogeographical regions of the
world
Slide 15
Continental birds Main biomes (vegetation zones) of the
world
Slide 16
Continental birds proportions of families, genera and species
shared depend on the effectiveness of the barriers and the
distances between the regions, both now and in the geological past
the longer an area has been isolated, the higher the taxonomic rank
of its endemics
Slide 17
Palaearctic region Continental birds Palaearctic region
Slide 18
46 mil km; more than twice as big as any other region within
each type of habitat, more species at E than W end of Eurasian
land-mass, due to the greater severity of the glaciations in the
west Continental birds
Slide 19
Palaearctic region 46 mil km; more than twice as big as any
other region within each type of habitat, more species at E than W
end of Eurasian land-mass, due to the greater severity of the
glaciations in the west marked seasonality Continental birds
Slide 20
Palaearctic region Atlantic has proved an effective barrier to
range extension in landbirds: Northern wheatear, Cattle egret,
Little gull, Fieldfare, Spotted sandpiper, Wilsons phalarope
Continental birds
Slide 21
Palaearctic region Bering Strait: dry land during glacial
periods (10.000 y ago) and holds series of islands (stepping
stones): Yellow wagtail, Northern wheatear, Arctic warbler, Snow
goose, Grey-cheeked thrush, Yellow-rumped warbler (tundra or boreal
forest) Continental birds
Slide 22
Palaearctic region Mediterranean Sea ca 5 mil y (early
Pliocene); less effective barrier with many islands: North African
species are Palaearctic in affinity (e.g. 165 species breeding but
not extending in sub- Saharan Africa): Duponts lark, Moussiers
redstart, Tristrams warbler, Algerian nuthatch supplemented by
Sub-Saharan species (White-rumped swift, Black-crowned
tchagra)
Slide 23
Continental birds Palaearctic region birds of N and C Sahara
predominantly Palaearctic, mainly at oases (Cirl bunting, Eurasian
spoonbill, Little owl) supplemented by Afrotropical species
extending N (Small buttonquail, Red-knobbed coot, Little green
bee-eater, Senegal thick-knee, Nile valley sunbird)
Slide 24
Continental birds Palaearctic region mountainous southwest
Arabia usually included in Afrotropical Region, while birds of
Persian Gulf and Iran predominantly Palearctic
Slide 25
Continental birds Palaearctic region mountainous southwest
Arabia usually included in Afrotropical Region, while birds of
Persian Gulf and Iran predominantly Palearctic at least 937
landbird species breed regularly in the Palearctic Region, which is
a low number and a low level of endemism (no endemic families, 9%
genera and 47% species restricted to the region)
Slide 26
Continental birds Palaearctic region localised endemics at
Madeira, Canary Islands, Cyprus, Azores, Corsica and Caucasus
Slide 27
Palaearctic region Continental birds Palaearctic region
Slide 28
Continental birds Palaearctic region within both regions,
proportion of shared species increase N, resulting in a Holarctic
distribution: e.g. Red crossbill, Northern goshawk, Common
goldeneye (boreal forest); Rock ptarmigan, Gyr falcon, Lapland
longspur (tundra); King eider, Sabines gull, Glaucous gull (arctic
ocean)
Slide 29
Continental birds Palaearctic region closely related species
point towards recent divergence in geological time (ancestral homes
differ between pairs); e.g 0.5 mil y for Northern harriers; 4.3 mil
y for Eagle owls; 7.9 mil y for Pygmy owls
Slide 30
Continental birds Ecologically equivalent and closely related
species in Eurasia and North America
Slide 31
Continental birds Palaearctic region some families poorly
represented, such as 7 and 2 species of Kingfishers (86 species)
and 1 and 2 species of Parrots (360 species) examples of poorly
represented Old World families in North America are Warblers,
Shrikes and Larks, and the representatives are often more closely
related to eastern Asian species examples of poorly represented New
World families in Eurasia are Wood warblers; Tyrant flycatchers and
Vireos
Slide 32
Continental birds Palaearctic region migrant passerines in both
regions are phylogenetically more different from each other than
the residents and short-distance migrants suggests that many
long-distance passerine migrants (mainly insectivorous warblers and
flycatchers) derived from essentially tropical families not true
for shorebirds and waterfowl
Slide 33
Continental birds Indomalayan (Oriental) region
Slide 34
Continental birds Indomalayan (Oriental) region 9.6 mil km;
mainly within the tropics; northern border (Himalayas) corresponds
with climate-vegetation ecotone includes Indonesian archipelago,
Philippines, Borneo, Sulawesi, Sumatra, Java and Bali transition
zone between Oriental and Australian Regions called Wallacea; 120 m
lower sea level during glaciations, when Sunda shelf was connected
to continental Asia; deep water channel east of Sunda shelf
contains oceanic islands such as Moluccas and Lesser Sundas
Slide 35
Continental birds Boundary between Indomalayan and Australasian
faunas
Slide 36
Continental birds Indomalayan (Oriental) region not known till
when Philippine Islands were attached to SE Asia, Sulawesi may
never have been connected to mainland Asia; more avian affinities
with Philippines and Lesser Sunda Islands than with Sumatra and
Borneo 3rd richest Region with 1697 species; 3 endemic families
(Leafbirds, Asian frogmouths and Bearded bee-eaters), 129 endemic
genera, 1184 endemic species (70%)
Slide 37
Continental birds Indomalayan (Oriental) region
Slide 38
Continental birds Indomalayan (Oriental) region major wintering
area for east Palaearctic breeding birds shares most families (but
not species) with Africa, probably because of connection by broad
stretch of tropical habitats through Middle East till Miocene
(often considered single Palaeotropical Region for plants)
Slide 39
Continental birds Indomalayan (Oriental) region at family level
both regions share Broadbills, Bulbuls, Sunbirds, Weavers,
Honeyguides family Phasianidae particularly well represented, and
centre of radiation for Pittas, Laughing thrushes, Drongos,
Flowerpeckers
Slide 40
Continental birds Indomalayan (Oriental) region
Slide 41
Continental birds Indomalayan (Oriental) region richness partly
results from fusion of 3 separate faunas originating at different
land-masses, and infiltration from at least 2 others; some regions
isolated for long periods; inclusion of many islands (e.g.
Philippines 7100 islands) with high endemism (Philippines: 43% of
403 breeding species endemic; Sulawesi 36% of 247 species) strong
difference between SE part of Eurasia and rest of land- mass due to
effectiveness of Himalayan chain and Tibetan plateau, abundance of
islands, and tropical forest belt
Slide 42
Continental birds Afrotropical (Ethiopian) region
Slide 43
Continental birds Afrotropical (Ethiopian) region mainly
tropical region; south of the Sahara and Madagascar, Comoro,
Seychelles and Mascarene Islands (islands sometimes separated as a
distinct Malagasy Region) northern border poorly defined across
Arabia ca 21 mil km (1.25 mil south of tropics)
Slide 44
Continental birds Afrotropical (Ethiopian) region main
vegetation types run in latitudinal belts, becoming more arid and
open north- and southwards from the equator, but basic pattern is
complicated by topography markedly seasonal climate with distinct
dry and wet seasons
Slide 45
Continental birds Afrotropical (Ethiopian) region although
similar in latitude as Neotropical Region, it contains less than
half as many landbird species (ca 1950 regional breeders), partly
because tropical and montane forest cover much smaller areas and
high arid plateaus are more extensive
Slide 46
Continental birds Afrotropical (Ethiopian) region among
passerines, Weavers, Waxbills, Starlings, Larks, Shrikes and
Sunbirds are especially well represented. Also rich in Francolins,
Bustards, Barbets, Honeyguides and Cisticolas, but poor in Parrots
and Woodpeckers.
Slide 47
Continental birds Afrotropical (Ethiopian) region both species
of Oxpecker have evolved in close association with large
herbivorous mammals
Slide 48
Continental birds Afrotropical (Ethiopian) region 11 endemic
families of mainland Africa and 6 of Malagasy mostly contain small
numbers of species, and some are represented among fossils from
Europe and North Africa
Slide 49
Continental birds Afrotropical (Ethiopian) region main centres
of endemism: Ethiopian massive, Cameroon Mountains, East African
Mountains, Somali and Namibian arid zones, Gulf of Guinea Islands
(Princip, So Tom)
Slide 50
Continental birds Afrotropical (Ethiopian) region hard to
decide in which direction colonization took place, but some seem
certain: e.g. two African Pittas, four African Broadbills, eight
African Drongos (from SE Asia); three African Wagtails, Longbilled
pipit (from Eurasia); Cisticola juncidis, Ploceus weavers,
Estrildinae (to SE Asia) enormous influx from Palaearctic migrants
(about a third of all species from that region), some species
occasionally breed in Africa
Slide 51
Continental birds Afrotropical (Ethiopian) region Malagasy
subregion: Madagascar fourth largest island on earth, ca 400 km
from Africa; thought to have broken away from Gondwanaland as a
unit with India > 100 mil y ago, then separated from India 80-85
mil y ago.
Slide 52
Continental birds Afrotropical (Ethiopian) region some species
such as the extinct Elephantbirds may date back to this period;
other species may have arrived later by cross-water flights
Slide 53
Continental birds Afrotropical (Ethiopian) region various
levels of endemism (from families to subspecies) attest to the
continuation of the colonization process over long period of time.
Some part of the avifauna is relictual, e.g. fossil birds similar
to Madagascan ground-rollers from North-America
Slide 54
Continental birds Afrotropical (Ethiopian) region Avifauna of
Madagascar relatively poor (198 breeding landbird species), but
about 25% of the genera and >50% of species endemic. Small
average number of species per genus implies low rate of recent
speciation (or immigration) or high rate of recent extinction (low
speciation:extinction ratio). One adaptive radiation has given rise
to diverse range of songbird species, resembling bulbuls, babblers
and warblers; another has given rise to 14 species of Vanga shrikes
(classified in 12 different genera) Mascarenes, Seychelles and
Comoros derived birds mainly from Madagascar (sharing 22
landbirds); many flightless species went extinct (e.g. Dodo)
Slide 55
Continental birds Australasian region
Slide 56
Continental birds Australasian region comprises eastern
Indonesian Islands, New Guinea, Australia, New Zealand and
neighbouring Pacific Islands;
Slide 57
Continental birds Australasian region total area ca 0.9 mil km;
large proportion semi-arid or arid; 40% in the tropics; Australia
is the dries continent; bird movements are mainly constrained by
expanses of desert rather than by mountain ranges
Slide 58
Continental birds Australasian region Australia has been
physically isolated for more than 55 mil years, giving rise to a
unique fauna derived from Gondwanan heritage; repeatedly connected
to New Guinea and Tasmania, most recently 10.000 years ago;
relatively little migration to and from other regions lack of
glaciations and frequent fires have provided nutrient-poor
conditions and some of the least productive seas on earth
Slide 59
Continental birds Australasian region annual variations in
rainfall greater than within-year seasonal variations (El Nio
Southern Oscillation); ca 1/3 of all bird species nomadic, and
large proportion nest in tree hollows (ca 11% are obligate cavity
nesters; about twice as many as on any other continent) 1592
landbird species; 2nd richest in landbird species per unit area;
high speciation due to fragmented nature of forests and many
islands; 25% of families, 61% of genera and 89% of species endemic;
2nd highest degree of endemism (after Neotropics) avifaunal
differences between Guinea, Australia and Tasmania are mainly
related to habitat difference
Slide 60
Continental birds Australasian region parrots, pigeons and
doves, kingfishers and honeyeaters very well represented (latter
most diverse group in Australia and New Guinea)
Slide 61
Continental birds Australasian region curious birds are
Birds-of-Paradise, Bowerbirds, Megapodes, Kiwis, etc.
Slide 62
Continental birds Australasian region based on fossils, major
components inherited directly from Gondwanaland (earliest know
passerine early Eocene, ca 55 mil y ago); autochthonous component
also includes Ratites, Penguins and possibly Lyrebirds, Pigeons,
Parrots, Kingfishers relatives (same families) in Africa and South
America reflect a common origin; some families currently restricted
to region are represented among Eocene/Oligocene fossils from
Eurasia (Owlet- nightjars, Frogmouths, etc)
Slide 63
Continental birds Australasian region DNA-DNA hybridization
indicates that passerines mainly result from endemic radiation
within Australia rather than from successive colonization from
Eurasia; majority fall into 3 distinct assemblages with convergence
in form and habit towards unrelated birds in northern
hemisphere
Slide 64
Continental birds Australasian region Relationships and
divergence of Australian passerines
Slide 65
Continental birds Australasian region 2nd major component from
Palearctic-Oriental regions where close relatives are now found,
followed by secondary radiations (e.g. Waterbirds, Raptors, Swifts,
Pittas, Swallows, Thrushes, Silver-eyes); show varying degrees of
differentiation (including distinct genera)
Slide 66
Continental birds Decline in species numbers and diversity
between Afrotropical-Indomalayan regions and Australasia
Australasian region
Slide 67
Continental birds Australasian region very few characteristic
Australian genera breached Wallaces line to reach the oriental
Region, and none reached Africa; unequal exchange between
continents may reflect competitive superiority of members of one
avifauna
Slide 68
Continental birds Australasian region
Slide 69
Continental birds Australasian region New Guinea is tropical,
mountainous and wet, close to the Oriental Region and has rich
avifauna (i.e. more species than Australia); centre of distribution
of Birds-of-Paradise, Bowerbirds, Cassowaries, Megapodes and
Crowned pigeons New Caledonia separated from Gondwana about the
same time as New Zealand, and has a poor avifauna (71 species),
including the flightless Kagu (separate family), 4 other endemic
genera and 14 endemic species
Slide 70
Continental birds Australasian region avifauna of New Zealand
has 3 components: ancient group, Australian colonists, and
Holarctic colonists new Zealand wrens and extinct Moa preceded
split with Australia; other ancient species (without close
relatives elsewhere) comprise Wattlebirds (e.g. Saddleback), Kokato
and the extinct Huia and New Zealand thrushes insular influences
are seen in flightlessness, lack of sexual dimorphism, and
melanistic forms (common cause: lack of selection pressure in
absence of mammalian predators) 2nd component (Australian origin)
includes Dollarbirds, Parrots,
Slide 71
Continental birds Australasian region in recent times, habitat
shifts due to anthropogenic activity increased chances of vagrant
establishment (at least 8 Australian species during last 150 y) 3rd
component (Holarctic origin) includes species such as South Island
(Pied) Oystercatcher and New Zealand Scaup
Slide 72
Continental birds Australasian region
Slide 73
Continental birds Australasian region like Madagascar, New
Zealand has very low species-per-genus ratio suggesting recent
extinctions and little recent speciation mt DNA in museum specimens
suggest major genetic bottleneck ca 28 mil y ago (Oligocene) and
radiation from one/few mitochondrial lineages within each group New
Zealand experienced very different history from rest of Australia
(colder, frequent glaciations and volcanic activity, resulting in
more fertile soils)
Slide 74
Continental birds Nearctic region
Slide 75
Continental birds Nearctic region North America N of the
tropics and Greenland; S border usually placed through Mexico,
along N edge of the tropical rain forest (climate-vegetation
boundary) covers ca 21 mil km landmass and 2 mil km ice (Greenland)
in contrast to Europe, major topographical features extend
longitudinally; hence areas E/W of Rockies have large numbers of
exclusive species despite similar habitats; smaller areas of
endemicity on mountain/lowland areas
Slide 76
Continental birds Nearctic region
Slide 77
Continental birds Nearctic region also latitudinal change in
avifauna, with climatic and vegetation belts increasingly better
defined northwards 732 regular breeding species, less than in any
other region; no endemic bird families, but 19% genera and 54%
species endemic
Slide 78
Continental birds Nearctic region North American continent
connected with Europe (via Greenland) in early tertiary and
intermittent connections with Asia across Bering Strait bridge
(only 10.000 y ago); connection with South America occurred ca 3.5
mil y ago (Pliocene) as Central America is well vegetated, much
less separation of Nearctic-Neotropical avifaunas than of
Palaearctic-Afrotropical S half of North America was humid and
tropical as far N as San Francisco/Washington DC during 1st half of
Tertiary, permitting evolution of tropical North American fauna
(distinct of South America); intermingled when Panamanian
land-bridge established
Slide 79
Continental birds Nearctic region avifauna consists of 4
elements: (i) old indigenous (Wrens, Dippers, Gnatcatchers, Silky
flycatchers, American sparrows, Motmots), (ii) young Holarctic
(trans-atlantic connection with Europe but origin uncertain:
Cranes, Grouses, Thrushes; (iii) recent immigration from Asia
(Horned lark, Brown creeper, Pipits, Nuthatches, Corvids, Tits,
Kinglets, Barn Owl, Hirundines); (iv) immigrants from South America
with major radiation in North America (Tyrannid flycatchers)
Slide 80
Continental birds Nearctic region
Slide 81
Continental birds Nearctic region Greenland mostly considered
part of Nearctic Region; among 59 regular breeders, 38 circumpolar,
8 from Europe, 13 from Eurasia as almost whole of Greenland was
ice-covered until 6.000 years ago, much of its avifauna results
from recent immigration; yet, its Redpolls are considered
subspecifically endemic
Slide 82
Continental birds Neotropical region
Slide 83
Continental birds Neotropical region includes Central and South
America, West Indies and other islands near South America (incl.
Galapagos and Falklands); ca 18.2 mil km mainly covers tropical
forest, but also desert, grassland (pampas) and temperate/montane
habitat
Slide 84
Continental birds Neotropical region
Slide 85
Continental birds Neotropical region a few tropical species
(Trogon, Chachalaca) extend into North America, while some Nearctic
species such (e.g. Turkeys) extend into South America Central
America contains mix of old indigenous species and recent invadors
from South America (Tinamous, Jacamars, Puffbirds, Toucans,
Ovenbirds, Antbirds, Manakins, Cotingas) northward spread of
open-country species due to destruction of former forest
barriers
Slide 86
Continental birds Neotropical region
Slide 87
Continental birds Neotropical region contains longest mountain
range (Andes) with central high desert (Altiplano) holding largest
expanse of salt; Amazon (> 5000 km) drains 40% of continent and
acts as significant dispersal barrier; largest seasonal swamp
(Pantanal, > 60.000 km), true desert (Atacama) richest in
breeding bird diversity (3370 breeding species, 2 endemic orders,
20 endemic families, 686 endemic genera, 3121 endemic species);
shares 7% species but 65% families with nearctic Region highest
level of endemism reflects ancient and distinctive evolutionary
history many migrant species from North America, mainly wintering
in forest
Slide 88
Continental birds Neotropical region South America was isolated
as a giant island continent for more than 30 million years
Slide 89
Continental birds Neotropical region characteristic families
(Guans, Ovenbirds, Woodcreepers, Ground antbirds, Tyrant
flycatchers, Cotingas, Manakins, Puffbirds, Gnatcatchers, Jacamars,
Motmots, Barbets, Toucans, Tapaculos, Tinamous) underwent extensive
evolutionary radiation during Pliocene and Pleistocene (1137
species, i.e. > 10% of all species)
Slide 90
Continental birds Neotropical region some endemic species could
be relicts from former widespread distributions also many endemic
fresh/saltwater birds (Torrent duck, Coscoroba swan, Steamer duck);
however Cranes, Bustards, Hornbills, Corvids, Titmice, Nuthatches,
Treecreepers and Shrikes largely absent
Slide 91
Continental birds Neotropical region diversity due to (i)
extent of rain forest, (ii) N- and S-American fauna mixing at end
Pliocene, (iii) high regional endemism, (iv) fewer Pleistocene
extinctions due to less drastic glaciations, (v) speciation due to
long isolation, (vi) pronounced altitudinal zonations, (vii) recent
human colonization contains ca 90% of all suboscine birds, while
dominant oscines (> 4000 species worldwide) proportionally least
abundant Great American Interchange: more species colonized from N
to S than vice versa (Tanagers, Cardinals, Thrushes, Pipits, Horned
lark, Short-eared owl) flightless ratites of Africa, South America
and Australia probably remnants of former Gondwana
Slide 92
Continental birds Neotropical region South America and Africa
share various families (Trogons, Parrots, Jacanas, Painted snipes,
etc) but only 17 species; possibly as a result of ocean crossing
via stepping stones (ancient volcanos in south Atlantic)
Slide 93
Continental birds Neotropical region West Indies (Greater and
Lesser Antilles, Hispaniola, Carribean) have impoverished avifauna
(280 breeding species, 31 endemic genera, 150 endemic species)
received by dispersal; level of endemism surprisingly high given
proximity of both North and South America
Slide 94
Continental birds Neotropical region Galapagos, Falklands and
Juan Fernandez archipelago received most of their fauna from
adjacent parts of South America
Slide 95
Continental birds Oceania
Slide 96
Oceania Pacific Ocean occupies > 1/3 of earths surface (>
166 mil km); more than 23.000 small (tropical and subtropical)
islands, mostly volcanic, mainly in C and SW parts of ocean divided
into 3 regions: Micronesia and Melanesia (west) and Polynesia
(central); islands only cover 46.632 km (> 50% contributed by
three islands; e.g. Hawaii); some coral atolls (Tuomota
archipelago) below 7m altitude avifauna derived by cross-water
colonization; hence small number of taxa and strong affinities with
nearest continent; largest families are Whistlers, Doves,
Flycatchers, Rails, Parrots and Honeycreepers
Slide 97
Continental birds Oceania
Slide 98
Oceania islands fall into 5 biogeographical regions, but
central Pacific ones usually treated as Oceania; 187 landbirds in
23 families; represents 20 x species density of richest continent;
38% genera and 87% species endemic striking examples of recent
species formation and faunal attenuation, i.e. successive families,
genera and species dropping out with increasing distance from
continental source
Slide 99
Continental birds Oceania Hawaiian archipelago more than 4000
km off north America, yet still containing most diverse island
fauna; half of avian colonizers from North America; many species
extinct following human colonization
Slide 100
Continental birds Oceania avifauna of Oceania most severely
impacted
Slide 101
Continental birds Antarctica
Slide 102
Antarctica comprises main continent of Antarctica and all
islands, sea ice and ocean northwards to Antarctic Convergence
remaining fragment of ancient Gondwana which drifted to present
position over south pole; colder than arctic 14.3 mil km covered
with thick glacial ice which is unsuitable for birds; at the end of
summer, sea freezes from shoreline outwards (ca 3 km/day; doubling
size continent by end of winter) no landbirds on main land-mass,
seabirds dominated by Penguins and Petrels; sub-antarctic islands
(South Georgia, Kerguelen, Macquarie) hold 4 Ducks, 1 Pipit, Common
starling and Lesser redpoll (both self-introduced from New Zealand)
and introduced Rail Shearwaters, Gadfly petrels and endemic
landbirds north on temperate sub-antarctic islands (Tristan da
Cunha, Chatam)
Slide 103
Conclusions Species numbers and diversity overall, about 91% of
landbird species are only found in a single biogeographical region
moving through taxonomic hierarchy, distributions change
progressively from restricted to widespread; only 4 out of 23
landbird orders are represented in a single biogeographical region
differences can be attributed to greater age of higher taxa and
greater opportunities through time for wider dispersal regions
differ in numbers and densities of breeding birds and of species
per family, due to (i) different past events of autochthony,
colonization and in situ speciation (versus extinction), (ii)
K-values to support large numbers of different taxa; (iii) past
extent of glaciation; (iv) human impact
Slide 104
Species numbers and diversity # species/mil km: (S) Neotropical
(3370/185) > Australasian (1592/179) > Afrotropical
(1950/93); (N) Oriental (1697/177) > Neartic (732/35) >
Palaearctic (937/20) at higher taxonomic levels, differences
between regions are less marked, with Afrotropical region emerging
as richest (breeding species of 54% families and 83% orders)
Neotropical region holds extremely high number of species per
family (average 47.5, Tyrannidae 544 species) and proportion of
endemic species and families; also has the most distinctive bird
fauna, followed by the Afrotropical, Australasian, Indomalayan,
Nearctic and Palaearctic each region has own dominant groups (large
numbers of species, large morphological and ecological diversity):
North America (Parulid warblers), South America (Tyrannid
flycatchers), Eurasia (Silviid warblers), Africa (Weaver finches),
Australia (Honeyeaters) Conclusions
Slide 105
Conclusions Percentage of landbird orders, families and species
that breed in 1-7 biogeographical regions
Slide 106
Meeting of faunas continental interchange is more marked in New
than Old World due to the absence of massive east-west barriers
(mountain, sea, desert) isolating temperate from tropical avifaunas
Tyrannidae, Vireonidae and Parulini are probably of tropical origin
whereas equivalent insectivores (Sylviidae, Muscicapidae, Turdidae
and Oriolini) are probably of Palaearctic origin faunal exchange is
predominantly unidirectional, depending on relative number of
species in each land area and relative competitiveness (i.e.
disproportionale colonization of South America by North American
mammals) Conclusions
Slide 107
Meeting of faunas distinctiveness biotas probably maintained by
resistance to invasion (e.g. by competition): if resident species
exploit all ecological opportunities, new species may have
difficulties to establish (especially when adapted to different
faunal backgrounds) alternatively, local adaptation may be more
important than competition introduced species mainly restricted to
man-made habitats, rarely penetrating remaining natural habitats
which continue to hold native birds based on fossil records, (i)
bird distributions have changed greatly since the start of the
Tertiary (ca 65 mil y ago) and (ii) many endemic families once
occurred in other regions as well Conclusions
Slide 108
Island birds
Slide 109
around 1627 landbird species occur only on island (ca 17% of
all non-marine species) combined for all islands, overall species
density nearly 4 times greater than averaged for continents islands
are also important for nesting seabirds (not included above)
percentage birds on islands is much higher than in other types of
animals due to their superior dispersal powers tropical Pacific
islands of Oceania collectively hold greatest density of bird
species (187 endemic landbird species) study of island birds have
had major influence on evolutionary and biogeographical theory;
behave like replicated experiments Island birds
Slide 110
Island types classified according to mode of origin
Slide 111
Island birds Relationships between species number, island size
and level of isolation
Slide 112
Decline in occurrence of (sub)families of breeding landbirds
from New Guinea eastwards on various Pacific Islands Island
birds
Slide 113
Sequence of island colonisation from a mainland source
Slide 114
Seabirds
Slide 115
seabirds generally do not follow same biogeographical patterns
as landbird species include ca 320 species (skuas, skimmers, gulls,
terns, auks, tropicbirds, boobies, gannets, shags, cormorants,
frigatebirds, penguins, loons, petrels, shearwaters, albatrosses);
5 of 8 groups entirely marine; distinction with landbirds not
always clearcut Seabirds
Slide 116
Seabird species following classification by Sibley & Monroe
1990 Seabirds
Slide 117
form only 3% of worlds bird species, despite fact that sea
water covers >66% of surface; however, collective biomass
probably outweighs landbirds dependence on land varies between
species; distribution mainly governed by latitudinal marine zones,
distribution of food within those zones, and location of nesting
places Seabirds
Slide 118
Seabirds Latitudinal biogeographical sea water zones
Slide 119
Procellariiformes (petrels) are most pelagic of all seabirds
Seabirds
Slide 120
capacity to exploit distant food-supplies being helped by: (1)
lower body T (38C) and thus lower energy demands (2) ability to lay
down subdermal fat and stomach oil (3) dynamic flight mode which
additionally conserves energy (4) ability to feed by day and night
(excellent olfactory sense) (5) ability of eggs to resist chilling
and chicks to become torpid Seabirds
Slide 121
very few seabirds species compared to landbirds; 3.3% species
on 71% Earth surface sea is one of the least productive ecosystems
per unit of surface area (only 0.25% of primary production) all
seabirds are carnivores (among vertebrates, species richness of
carnivores only 10% of herbivores) most seabirds are confined to
relatively shallow coastal areas, and all species are tied to land
for breeding Seabirds
Slide 122
throughout the evolutionary history of birds, sea areas have
remained interconnected; coastlines of all main continents either
connected or within flying distance of neighbouring continents
extreme mobility of most seabird species life at sea constraints
body designs, colours and sizes of a birds to a more narrow range
of options Seabirds
Slide 123
seabirds may have resisted extinction partly because of: (1)
their large geographical ranges (2) their widely separated, largely
inaccessible nesting sites (3) the fact that younger age classes of
many species tend to remain at sea away from vulnerable nesting
colonies (e.g. Short- tailed albatross) Seabirds