THE BIOGEOGRAPHIC SIGNIFICANCE

OF A LARGE, DEEP CANYON:

GRAND CANYON, SOUTHWESTERN USA

Lawrence E. Stevens

Grand Canyon Wildlands Council, Inc.

And Museum of Northern Arizona

Ascalapha 

odorata 

"Mariposa de la muerte" 
Biogeo...What?

The Spatial Distribution of Life,

Its Evolutionary History and Contemporar

• General large deep canyon (LDC) concepts • Four ways LDCs affect species ranges and ge• Examples •Test LDC biogeography hypotheses • Implications for management and research 

Stevens, L.E. 2012. The biogeographic significance of a large, deep canyon:Grand Canyon ofthe Colora

Southwestern USA. Pp. 169‐208 in Stevens, L.E., editor. Global Advancesin Biogeography. InTech Rijeka. ISBN: 978‐953‐51‐0454‐4.
GCE:

A crossroads 

of ecosystems

through evolutionary 

space and time.

2 geologic 

provinces,

4 biomes 

Contemporary Diversity:

~2200 plant spp.

~530 vertebrate spp.

>20K macroinvert spp?

But how and why are they 

distributed in relation to

GC as a landform?

GRCA 

GLCA 

GCE 
Muav

Gorge

Eastern

Basin

Western

Basin

Grand Canyon consists of Two Basins: 

Isolated Eastern Basin and a more open Wester

GC Rim Map: Billingsley and Hamp
Large, Deep Canyons are Light-limited Eco

SOL Atmosphere Ri

d

s

D

s

dtot

w

I 

L 

o

s

Ae 

Be 

Shaded Side 

As 

River 

E

Canyon Floor 

Exposed Side: 

sL = [(

wsinI)/sin(180

o-(B

e+A

e))]sin 

s

D = (

dtot/cos A

e)-

s

L

Shaded Side: If I >As then so = dtot/cosAs , else so 
0 

10 20 30 40 50 60 70 80 90 

100 

GC 

PR 

SG 

RG 

MC 

FF 

UGG 

Aisles 

MGG 

MG 

LC 

Geomorphic Reach 

% Potential Annual Solar

Energy Received 

Solar Energy Limitation Varies 

by Geomorphic Reach 
Solar Energy Received at Two East-facing Sp

Vaseys Paradise Spring, GCNP 

0 

20 40 60 80 

100 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Month 

M e a n % M o n t h l y 

S o l a r F l u x ( M J / m 2 ) 

Cliff Spring, GCNP 

0 

20 40 60 80 

100 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

Month 

M e a n % M o n t h l y

S o l a r F l u x ( M J / m 2 ) 

A B 
Gene flow and movement in large, deep cany

Barrier, corridor, refugial, and null effects

Corridor 

Barrier/Filter Barrier/Filter 

Barrier/ 

Filter 

Rim 

Rim 

Refugia 

Flow Direction 

Upstream 

Dispersal 

(wind, zoochory) 

Downst

dispe

Gravity dispersal 
Corridor Effects: Range extension of desert sp

through low elevation Colorado River corr

Desert trumpet Banded 

Chuckwalla

Claret‐cup
Corridor Effects: Range and Movem

Beaver

Humpback Chub Nathanial Galloway with 2 Col

otters in Utah, ca 1900.
Colorado Pikeminnow

Corridor Effects: Migration

American Avo

Yuma M

Monarch Butterfly

Osprey

CO Pikeminnow
Barrier/Filter Effects:

Across‐Canyon and Upstream‐Downst

Grand Canyon Ringlet

Jo

Saguaro cactus

Tassel‐eared & Kaibab Squirrels
Barrier/Filter Effects:

River Corridor Lockouts and Gilligan

Horned lizard – down to Lees Ferry

but not further downstream in GC

Creosote

Mile 169, n

Parryella filifolia – waifed from UT,non‐reproductive, 3 plants
Grand Ca

Sentry Milkvetc

Refuge Effects and Endemism

Grand Kaibab Indra Canyon Rattlesnake

Swallowtail

McDougall’s Flaveria Masked Clubskimmer
Rare Habitats with Endemic Specie

Old growth Ponderosa Pine ForestCavesCanyon rim edges

Desert and Plateau springs and streams, espec

wet meadows
Null Biogeographic Effects

Lined Sphinx

Raven

Litaneutria min

Desert Bighorn
Biogeographic Anomalies:

Expected Taxa That Are Rare or Missin

From The Inner Canyon

• Termites (rare) – insufficient retention of

woody material on steep canyon slopes

• Horned toads – insufficient low gradient terrac

• Rabbits – hawk migration route, predation;

rabbits fall poorly (colonization by gravity

• Kangaroo Rats – insufficient low gradient habit

variability in seed availability
LDC Landscape Effects

Percent of Species Affected 

Taxon No. Species Corridor Barrier Refuge 

Plants 1700 49 trace 10 

Landsnails 59 2 96 2 Tiger beetles 42 21 60 19 

Butterflies 140 6 0 4 

Mosquitoes 18 22 0 22 Fish* 24 96 17 13 

Herps 58 62 38 0 

Birds 330 27 trace * Mammals 61 20 8 2 

Approx., Mean 2400 species 34 25 8 *strong flow regulation impacts 

Corridor FX = Null FX > Barrier FX > Refuge FX

67% of species affected by Grand Canyon as a landscape fea
Biogeography Insights 

Continental and Regional Biogeography 

1. Biogeographic affinity affects assemblage composition: Neotropic

taxa at lower elevations, Nearctic taxa at higher elevations

2. Elevation effects analogous to latitudinal effects: Not for SR, but y

species density (SDEN), with a strong decrease in SDEN acro

3. Landform configuration affects species richness (SR): >50% of pla

and >75% of animal populations affected (esp. barrier, corr

Colonization History of CRE 

4. Taxon mobility affects species richness: Higher SR of volant speci

recently changed by climate, under-colonized landscape. 

5. SR attenuates upriver: Especially aquatic invertebrates and herpe

6. Levels of endemism are distinctive, with >30 endemic taxa, 

GCE as a Pleistocene and Holocene refugium. 
Management Considerations

• GCE is a mixing zone and refuge over geologic time• Corridor FX = Null FX > Barrier FX > Refuge FX,

>67% of species ranges , and likely gene flow affecte

• <10% of animal taxa sufficiently well known to assess 

• Endangered species are poor “umbrellas” for rare, en

No. Endemic Spp/

GCE Ecosystems
 

1.41.2

1

0.80.60.40.2

0

y = 2.518x + 0.2292

R2 = 0.3715

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

No. ES/GCE Ecosystem 
Sleepy Dogface 

Black Swallowtail Many-tailed 

Swallowtail Western Swallowtail 

Mourning Cloak Dainty Sulfur Buckeye Acastus Patch 

Queen Painted Lady Sister Grand Canyon Brown 

Common Butterflies of the Grand Canyon Ecoreg

Great Purple Hairstreak American Snout Pygmy Blue Common White 
Rarity Management

No. Endemic Spp/

GCE Ecosystems
 

1.41.2

1

0.80.60.40.2

0

y = 2.518x + 0.2292

R2 = 0.3715

Lentic aquatic 

Lotic aquatic 

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

No. ES/GCE Ecosystem 

* Understanding invertebrate rarity requires inventory, assessment a

biome, state, regional, national, and international spatial sc

• Endemism varies spatially (and temporally?), narrowly endemic t• Rare GCE invertebrates may not be rare elsewhere in AZ, the So

or North America 

* Are all endemic taxa worthy of conservation consideration? * Should we care about isolated populations (e.g., only population in 

if a taxon is otherwise widely distributed? 
Conclusions

• Many species new to science, much apparen

and some endemism (esp. invertebrates)

• Fewer than 10% of macroinvertebrate taxa a

vertebrates insufficiently well known to asse

or conservation challenges

• Occurrence in little‐recognized, poorly studi

habitats, such as springs and caves

• Endangered species are poor “umbrellas” fo

endemic taxa

GROW THE KNOWLEDGE !

Inventory, curate, database
Biogeographic Hypothesis Tests 

Continental and Regional Biogeography 

1. Does biogeographic affinity affect assemblage composition: 

Yes, Neotropical taxa at lower elevations, Nearctic taxa at higher elevations. 

1 

0 

500 

1000 1500 2000 2500 

0 .5 1 1 .5 2 2 .5 3 

Range 

Neotropical 

Elevation (m) 

Centered Nearctic 

Aquatic Heteroptera 
Ranges of 121 butterfly

and skipper species

55 

9 

0 

21 

1 

6 

15 

8 

3 

3 

12 

3 

Ranges of 18

mosquito species

6 

0 

2 

7 

4 

4 

Ranges o

tiger beetle 

N 

W 

S 

Affinity Varies by Taxon
Species-area analysis of aquatic Hemiptera as a funct

land area across elevation 

0.000 0.100 0.200 0.300 0.400 0.500 0.600 

Log 10 (S+1) : Log 10 A (km 2 ) 

0 500 1000 1500 2000 2500 3000 

Elevation (m) 
0 

5 

10 15 20 25 30 

South Rim Inner 

Canyon 

South 

River 

Corridor 

Inner 

Canyon 

North 

No

Upper CMiddle CLower C

Species Richness 

Zone 

GCE Herpetofaunal Species Richness in th