Effects of Soil Type and Fertility Effects of Soil Type and Fertility and Large Herbivores on East-and Large Herbivores on East-

African Savanna Small MammalsAfrican Savanna Small Mammals

Bradley J. Bergstrom

Biology Department, Valdosta State University, Valdosta, GA

Mpala Research Centre

Habitat Manipulations: Large-Herbivore Exclusion & Prescribed Burns

Rodent populations Rodent populations responded positively to responded positively to fencing (Keesing 1998)fencing (Keesing 1998)

Was it: a) release from Was it: a) release from diffuse competition for diffuse competition for resources, or b) improved resources, or b) improved cover?cover?

Burns should enhance forage, but Burns should enhance forage, but short-term effect negative on short-term effect negative on rodents due to loss of cover. This rodents due to loss of cover. This effect may persist, depending on effect may persist, depending on response of larger herbivores response of larger herbivores (Sensenig 2004), (Sensenig 2004),

Native Large Mammalian Herbivores“Megaherbivores”

Zebra: grazer, non-ruminant

Mixed Feeders, Ruminants

Black Cotton soilBlack Cotton soil

• Vertisol of volcanic originVertisol of volcanic origin• More productive grassland substrateMore productive grassland substrate• Dominated by Dominated by Acacia drepanolobiumAcacia drepanolobium• More sparsely bushedMore sparsely bushed• Single dominant small (Murid) rodent: Single dominant small (Murid) rodent:

Saccostomus mearnsiSaccostomus mearnsi

Saccostomus mearnsi (pouched mouse)

Red soil

• Sandy loamSandy loam

• More densely bushed, with greater More densely bushed, with greater diversity of woody speciesdiversity of woody species

• Less productive grasslandLess productive grassland

• Several co-dominant small rodents…Several co-dominant small rodents…

Acomys sp. (spiny mouse)

AethomysAethomys sp. (bush rat) sp. (bush rat)

Tatera sp. (gerbil)

ArvicanthisArvicanthis sp. (grass rat) sp. (grass rat)

Elephantulus rufescensMus musculoidesMus musculoides (pygmy mouse) (pygmy mouse)

Boma

• Cattle enclosure of traditional pastoralists• Cleared of woody vegetation• Ringed with cut thorn-scrub (Acacia)• Becomes highly enriched over years of use

Glade

• Abandoned boma site, attracts native Abandoned boma site, attracts native large herbivores (feeding and bedding)large herbivores (feeding and bedding)

• Dense grassy understory, woody plants Dense grassy understory, woody plants suppressedsuppressed

• Effect lasts for decades, sustained by Effect lasts for decades, sustained by herbivoryherbivory

• Some glades become closely cropped Some glades become closely cropped “grazing lawns”“grazing lawns”

Ungrazed Glade in Red SoilUngrazed Glade in Red Soil

Augustine and McNaughton (2006)Augustine and McNaughton (2006)

Ungrazed Glade in Black Cotton

• KLEE (Kenya Long-Term Exclosure KLEE (Kenya Long-Term Exclosure Experiment [Young et al. 1997] overlaid on Experiment [Young et al. 1997] overlaid on old gladesold glades

• Rankest grass on “Zero” plots; also dense Rankest grass on “Zero” plots; also dense on “W” plots (native ungulates, but not on “W” plots (native ungulates, but not elephant or giraffe)elephant or giraffe)

Methods• Live-trapping (Shermans) mid-August to mid-December• 100-trap grids and transects (10-m spacing), each

trapped 4 consecutive days and nights • Black Cotton sites: grazed, partly grazed, and ungrazed

glades; burned and unburned non-glades• Red-soil sites: grazed and ungrazed glades and non-

glades (“bush”)• Structural meas. of understory: dead/live stem density,

bare soil; grass height

KLEE South Glade: Total Small Mammals

0

2

4

6

8

10

12

14

16

Cattle Zero WC Wildl

Exclosure Category

No

. o

f In

div

idu

als

(MN

A)/

Cap

ture

s

Individuals P > 0.1

Captures P < 0.01

H'= 0.995 S = 3

H'= 1.061 S = 4

H'= 0.562 S = 2

H'= 0.60 S = 3

KLEE South Glade, Arvicanthis

0

2

4

6

8

10

12

14

Cattle Zero WC Wildl

Exclosure Category

No

. of

Ind

ivid

ua

ls/ C

ap

ture

s

Individuals P > 0.1

Captures P < 0.005

Black-Cotton Glade Herbivore Exclosure (KLEE South): Grass Height, Density & Coverage

0

5

10

15

20

25

30

35

C ZERO W WC

Mn Grass Ht (cm)/2

Live Stems

Dead Stems

% Bare Soil

**

ms

**

ns

Black Cotton: Ungrazed Glades (3), Grazed Glade, Grazed Nonglade

0

5

10

15

20

25

30

35

South Glade Central Glade North Glade Control Glade ControlNonglade

Ind

ivid

ua

ls (

MN

A)/

ha

Total Mammal P < 0.001

Saccostomus P = 0.001Arvicanthis P = 0.006

H' = 0.876 H' = 0.819 H' = 0.777 H' = 0.305

H' = 0

Red-Soil Glade Exclosures: High densities & dramatic treatment effect

Red-Soil Glade Plot 1

0

10

20

30

40

50

60

IN OUTGrazing Exclosure

Min

imu

m N

um

ber

Aliv

e

Aethomys

Tatera

Arvicanthus

Saccostomus

H' = 1.169

H' = 0

Red-Soil Glade Plot 2

0

10

20

30

40

50

60

IN OUTGrazing Exclosure

Min

imu

m N

um

ber

Aliv

e

Elephantulus

Tatera

Arvicanthus

Saccostomus

H'= 0.838

H' = .637

Red-Soil Glade Plot 3

0

10

20

30

40

50

60

IN OUTGrazing Exclosure

Min

imum

Num

ber

Aliv

e

Elephantulus

Tatera

Arvicanthus

Saccostomus

H' = 1.253

H' = 0.693

▪Treatment Effects: all P < 0.1 (Mann-Whitney) for Total Small Mammal and Three Most Common Species

Red-Soil Bush Exclosures: Half the densities of glades but still dramatic treatment effect

Red-Soil Bush Plot 1

0

5

10

15

20

25

30

IN OUTGrazing Exclosure

Min

imu

m N

um

ber

Aliv

e ElephantulusAethomysTateraArvicanthusSaccostomus

H' = 1.52

H' = 0.637

Red-Soil Bush Plot 2

0

5

10

15

20

25

30

IN OUTGrazing Exclosure

Min

imu

m N

um

be

r A

liv

e

AcomysElephantulusAethomysTateraMusSaccostomus

H' = 1.423

H' = 1.332

Red-Soil Bush Plot 3

0

5

10

15

20

25

30

IN OUTGrazing Exclosure

Min

imu

m N

um

ber

Ali

ve

Elephantulus

Aethomys

TateraArvicanthus

Saccostomus

H' = 1.115

H' = 0

▪Treatment Effect: Total Mammal P = 0.01, Individual Species P > 0.1 (Mann-Whitney)

Mean Grass Height per Sampling Station

0

5

10

15

20

25

30

35

40

45

Glade1 Glade2 Glade3

Heigh

t in cm

Inside HerbivoreExclosure

Outside HerbivoreExclosure

P< 0.001P< 0.0001P< 0.0001

Mean Grass Height per Sampling Station

0

5

10

15

20

25

30

35

40

45

50

Bush1 Bush2 Bush3

Heigh

t in cm

Inside HerbivoreExclosure

Outside HerbivoreExclosure

P< 0.0001 P< 0.0001 P< 0.0001

Percentage Bare Soil per Sampling Station

0

5

10

15

20

25

30

35

40

45

50

Glade1 Glade2 Glade3

Perc

ent (

%)

Inside HerbivoreExclosure

Outside HerbivoreExclosure

P= 0.013 P= 0.029 P= 0.0002

Percentage Bare Soil per Sampling Station

0

10

20

30

40

50

60

70

80

90

100

Bush1 Bush2 Bush3

Perc

ent (

%)

Inside HerbivoreExclosure

Outside HerbivoreExclosure

P< 0.0001 P= 0.0004 P= 0.12

151050

50

40

30

20

10

0

Mean Dead Grass Stems (hits/10-pin frame)

To

tal S

ma

ll M

am

ma

ls/h

a (

MN

A)

UB UB

U

BU

B CN

CG

MWC

Z

WC

W

Z

C

WC

W

Z

C

Regression R2=68.5%, P=0.00005.CN= Control Non-Glade; 9-ha burn plots B= burned, U= unburned. QuadraticBlack-cotton sites: Z,C,W,WC,MWC = KLEE glade plots; adjacent CG= Control Glade,

Live stems n.s. (P > 0.5)

1050

100

50

0

Mean Dead Grass Stems (hits per 10-pin frame)

To

tal S

ma

ll M

am

ma

ls/h

a (

MN

A)

RB-

RB-RB- RG-

RG-RG-

RBRB

RBRG

RG

RG

outside controls = RG-, RB-. Linear Regression R2=54.5%, P=0.006.Inside Red-soil 0.5-ha Exclosures in Glade and Non-glade (Bush)= RG, RB. In adjacent

Live stems, R2 = 35.4% (P = 0.041)

Small Mammal Densities and Species Richness (Min-Max per plot)

BLACK RED

Ungrazed

N/ha S

Grazed

N/ha S

Ungrazed

N/ha S

Grazed

N/ha S

Bush n/a 2-7 2 30-50 4-5 181 4

Glade 30-50 3-4 8-12 1-2 50-120 4 4-12 1-2

10-10 adjacent to exclosures

Conclusions I

• Both Soil Types: Arvicanthis (diurnal) found only in exclosures.

• Saccostomus dominant in all Black-cotton treatments and controls, but limited to exclosures in Red-soil (grazing yields bare patches in Red-soil, more so than Black Cotton).

• Black Cotton small-mammal density and diversity naturally lower than Red Soil (“matrix,” i.e., grazed, non-glade controls).

• Red Soil species richness 2X higher (7-8 species caught > 2 times vs. 4 species for Black Cotton)

• Red Soil grazing treatment effect more dramatic; glades all grazing lawns, densities inside 2X.

Conclusions II

• Small-mammal density strongly positively related Small-mammal density strongly positively related to Grass Height and Grass Density—especially to Grass Height and Grass Density—especially dead stems—within each soil type.dead stems—within each soil type.

• Small mammals avoid high-nutrient foraging Small mammals avoid high-nutrient foraging areas without sufficient cover.areas without sufficient cover.

• Large-mammal herbivory removes small-Large-mammal herbivory removes small-mammal cover.mammal cover.

• Question:Question:• What is natural? e.g., where is/was What is natural? e.g., where is/was ArvicanthisArvicanthis

naturally common?naturally common?

Literature Cited• Augustine, D.J., and S.J. McNaughton. 2006. Interactive effects of ungulate

herbivores, soil fertility and variable rainfall on ecosystem processes in a semi-arid savanna. Ecosystems 9:1-16.

• Keesing, F. 1998. Impacts of ungulates on the demography and diversity of small mammals in central Kenya. Oecologia 116:381-389.

• Sensenig, R.L. 2004. Spatial ecology of fire in an East African savanna: effects of burn size and patchiness on the foraging ecology of herbivores of varying body size. Proposal to NSF for Dissertation Improvement Grant.

• Young, T.P., B. Okello, D. Kinyua, and T.M. Palmer. 1997. KLEE: a long-term multi-species herbivore exclusion experiment in Laikipia, Kenya. African Journal of Range and Forage Science 14:94-102.

Acknowledgments Valdosta State University

National Science Foundation

Mpala Research Centre

Truman Young

Ryan Sensenig

Bernard Agwanda

National Museums of Kenya

John Mpaiyan

Jake Goheen

Todd Palmer

Rob Pringle

Corinna Riginos