Effects of fire on small mammals of the Koanaka Hills, Northwestern Botswana

2015·0.92 MB·English

by  Thies, Monte L., author

TEXAS TECH UNIVERSITY
Natural Science Research Laboratory
Occasional Papers
Museum of Texas Tech University Number 330 10 February 2015
Effects of Fire on Small Mammals of the Koanaka Hills, Northwestern
Botswana
Monte L. Tries and Patrick J. Lewis
Abstract
In June 2008, a series of 230 small mammals were eolleeted from the Koanaka Hills of
northwestern Botswana as a referenee eolleetion to aid in defining ehanges in the regional elimate
over the past ~2 million years. Just two months after this eolleetion was made, large expanses of
northwestern Botswana were eonsumed by wildfire, ineluding the study site. Efforts to evaluate
the efifeets of eatastrophie fire on wildlife diversity and post-fire genetie eomposition in southern
Afriea are uneommon. The oeeurrenee of this fire immediately after a eomprehensive trapping
effort allowed unantieipated researeh questions to be addressed. To evaluate the efifeet of large-
seale fire on small mammal speeies abundanee and diversity, we returned to the Koanaka Hills
in July 2009 and replieated the eolleeting efforts of 2008, whieh yielded 510 small mammals.
Analyses of the trapping data indieate only minor differenees in speeies abundanee and diversity
among areas sampled.
Key words: Botswana, fire, rodents, speeies diversity
Introduction
A relatively reeent diseovery of mierovertebrate Within three months of the initial eolleeting trip
fossils, attributed to barn owls as the aeeumulating to the Koanaka Hills, the region was eonsumed by a
agent, in a Pleistoeene eave system in the Koanaka Hills eoneentrated bush-fire (M. Gabadirwe, Botswana Na¬
of northwestern Botswana (Piekford and Mein 1988; tional Museum, pers. eom.). Opportunities to evaluate
Williams et al. 2012) and a relatively poor understand¬ the effeets of large-seale eatastrophie fire on speeies
ing of the region’s modern fauna prompted a eolleeting diversity and genetie diversity and ehanges within
trip in 2008 to doeument the area’s small mammal, populations are unfortunately not very eommon, and
amphibian, and reptile diversity. The primary purpose the fortuitous oeeurrenee of these fires so soon after a
of this effort was to obtain a eomparative referenee eol¬ eomprehensive trapping effort allowed unantieipated
leetion for the interpretation of fossil fauna eolleeted researeh questions to be addressed.
by Williams etal. (2012). In June 2008, a series of 230
small mammals, 38 reptiles, over 80 owl pellets, and Small mammal eommunities are influeneed
hundreds of Plio-Pleistoeene vertebrate fossils were direetly by fire and indireetly by burn effeets on plant
eolleeted from the Koanaka Hills. eommunity strueture. Researeh into the effeets of
2 Occasional Papers, Museum of Texas Tech University
fire on small mammals in the tallgrass prairies of the 1.7 aere plot of ehaparral serub in Malibu, California,
United States has shown that direet effeets may in- within days of major eanyon fires in 1957 (Chew et al.
elude burns, heat stress, asphyxiation, physiologieal 1959). In a study eomparing rodent survivability in
stress, trampling, and predation during eseape from burned versus unburned areas of South Afriea, speeies
fire (Kaufman et al. 1990). Speeies with aboveground adapted to more open environments aetually preferred
nests may perish direetly during the fire (Simons 1989, burned areas whereas speeies preferring overhead eover
1991); however, burrowing rodents are more likely appeared to leave the area, whieh was presumed to be
to survive if burrow depth is adequate (Howard et al. a defense against inereased risk of aerial predation
1959). Small mammals also may fiee from their burrow (Christian 1977). Breeding pereentages, survivorship,
or nest during a fire and establish a new burrow or nest and movement distanees of Desmodillus auricularis
site away from the burned area. Physiologieal stress and Gerbillurus paeba were similar on burned and
indueed by fire ean impaet small mammal populations unburned areas, suggesting that survival of these spe¬
through abortion of litters or abandonment of young. eies on burned areas is an adaptation to desert existenee
The primary infiuenees of fire on small mammal eom- rather than to fire altered habitat (Christian 1977).
munities, however, are often indireet effeets through Other studies (e.g., Ojeda 1989; Simons 1989, 1991;
ehanges in vegetation eomposition and strueture that Kirkland et al. 1996; Monroe et al. 2004) demonstrate
alters the quantity or quality of food, availability of nest speeies eomposition and demographie shifts as a result
sites, predator/prey interaetions, and rates of parasitism of fire, but usually report effeets of small eontrolled
and disease (Kaufman et al. 1990). fires rather than fires of a seale eomparable to the Ko-
anaka Hills fire of 2008 that was reported to eonsume
One of the earliest publieations on the devastat¬ an estimated 650+ km^ [Mmegi Online: www.mmegi.
ing effeet of wildfire on wildlife reported 43 eareasses bw, 8 Oet. 2008, Vol. 25 (147); 30 Oet. 2008 Vol. 25
eomprised predominantly of rodents and rabbits on a (160); 17 Nov. 2008 Vol. 25 (169)].
Study Area
Together with the Aha and Gewihaba Hills, the frequeney with whieh these pans eontain water, nor the
remote Koanaka Hills (20° S, 21° E) form part of a duration for whieh they hold water, is known. No signs
series of dolomite uplifts in northwestern Ngamiland, of water in the pans were obvious during the months
Botswana (Fig. 1; Cooke 1975). Loeated 100 km of June-August in 2007, 2008, or 2009. The pans are
due west of Tsau on the southwestern margin of the eomprised of ealeareous elays overlying ealerete and
Okavango River Delta and 22 km southwest of the are separated from the roeky outerops of the hills by
Gewihaba Hills, the Koanaka Hills are eomprised of dense serub brush. Annual temperature variation near
three separate hills. Two hills, Koanaka North and the Koanaka Hills varies from -8.5°C to 42.2°C (Bo¬
Koanaka South (Fig. 2), are separated by ea. 0.5 km tswana Department of Meteorologieal Serviees 2009).
and the third hill is 12 km to the west. Composed During the 2008 eolleetion period daytime temperatures
primarily of dolomitie roeks and breeeia infills (Cooke averaged 26°C, nighttime temperatures averaged 2°C,
1975) with maximum elevations of ea. 50 m above the and there was no preeipitation. During the 2009 eollee¬
surrounding plains, they represent the only topographie tion period daytime temperatures averaged 28°C, night¬
relief for over 20 km. time temperatures averaged 5°C, and light preeipitation
oeeurred for less than 10 minutes on one day. Small,
The habitat around the hills is a semi-arid, dense, regularly oeeurring ground fires are known to oeeur in
shrub savanna, referred to as the Kalahari Thirstland the area; however, duration, frequeney, and intensity
(Smithers 1971; Piekford and Mein 1988). Annual are not well doeumented.
rainfall of 400-450 mm oeeurs primarily during the
austral summer months (van Regenmortel 1995). Two In 2008, a baseline vertebrate inventory for the
pans (ephemeral ponds) are loeated approximately area around Koanaka South was eompleted (Bauer et
200 m west of Koanaka South, although neither the al. 2009; Ferguson et al. 2010) to ereate a eomparative
Tries and Lewis—Effects of Fire on Small Mammals in Botswana 3
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Figure 1. Map of the Koanaka Hills, Ngamiland, Botswana (modified from Bauer et al.
2009) showing the location of the Koanaka Hills (starred). The inset shows the locations
of Koanaka North, Koanaka South, and primary pan in association with the waterhole.
4 Occasional Papers, Museum of Texas Tech University
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Figure 2. Magnified inset of Figure 1i with locations of the six Koanaka Hills study areas. Polygons indicate
limits to trapping areas within each study area.
collection of modern skeletal material for interpretation Following fires in the area in late 2008, the objectives
of fossil fauna collected by Williams et al. (2012), and of the original project expanded to assess changes
to aid in paleoclimatic reconstruction for the region. in small vertebrate species diversity and abundance
At that time, due largely to time constraints and the within and around Bone Cave and the Koanaka Hills.
primary focus being development of a reference skeletal Results from the effects of fire on the herpetofauna
collection, no efforts were made to conduct quantita¬ were reported in Kennedy et al. (2012) and the effects
tive habitat characterizations of the sampling localities. on small mammals are reported herein.
Methods
As part of an ongoing investigation of the past for the 2009 resampling effort duplicated field methods
and present fauna of the region, small mammals were used in 2008, with three of the four original members
surveyed within the vicinity of the Koanaka Hills, of the 2008 mammal trapping team returning for the
Ngamiland, Botswana, from 17 June to 2 July 2008 replicated efforts. Trapping efforts utilized similar
(Bauer et al. 2009; Ferguson et al. 2012; Kennedy et numbers and styles of traps set in lines radiating out
al. 2012). Secondary efforts to document changes in from GPS points recorded in 2008, similar baits, and
small mammal species diversity and abundance of the were placed along similar transects whenever possible.
Koanaka Hills stemming from reports of expansive fires
of 2008 (after our initial trapping efforts) resulted in a Six trapping areas were established in 2008 (Fig.
resampling effort conducted 7-13 July 2009. Protocols 2) to represent primary habitat variability on and around
Tries and Lewis—Effects of Fire on Small Mammals in Botswana 5
Koanaka South in an effort to sample the diversity versity (Eubboek, TX). Tissues were eolleeted and
of small mammals in the area as fully as possible. A preserved in either 95% ethanol. A list of unproeessed
general eheeklist of possible speeies in the proximity of animals was made prior to any release; however, the
the Koanaka Hills was eompiled from works published inaeeuraey of speeies identifieation without adequate
by Smithers (1971), de Graaff (1981), and Skinner and DNA samples for verifieation foreed us to remove the
Chimimba (2005) along with a review of available released speeimens from any inelusion in subsequent
information on habitat preferenee and generalist/spe- data analyses. With the assistanee of a larger field team
eialist behavior of those speeies expeeted. Areas were in 2009, all speeimens in the resampling effort were
seleeted based on degree and type of general ground proeessed and none were released.
eover (e.g., bare ground and/or roeky outerops, sparse
serubby vegetation, heavy grasses, and presenee of The vast majority of speeimens were eolleeted
larger shrubs and trees; Fig. 3). Area 1 and areas 2-6 with Sherman traps; however, Crocidura hirta and
were restrieted to within a 2 km radius of a primary Mus spp. also were eaptured using pitfall arrays and
waterhole and Koanaka South, respeetively, based on drift fenees set near the base of Koanaka South. One
ranging behavior of barn owls {Tyto alba) in North pitfall array was Y-shaped with a pitfall trap on the end
Ameriean and European telemetry studies (Taberlet of eaeh arm and one in the eenter. Two arrays were
1983; Colvin 1984; Taylor 1994). established with straight fenees and three pitfall traps;
traps within eaeh array were plaeed approximately 3m
Sampling for small mammals in both years eon- apart. Eaeh array was built with 0.5 m tall drift fenee
sisted primarily of line transeets of Sherman live traps, made of blaek plastie sheeting with wooden stakes, and
establishing pitfall arrays, and mist nets that were set 5-liter buekets were used for the pitfall traps. Arrays
in representative habitats. Museum speeial snap traps were eheeked twiee daily, onee just after sunrise and
also were used to seleetively sample for arborial speeies onee just before sunset.
in seleet habitats; however, they yielded no speeies in
addition to those also being taken with Sherman traps. Bats were eolleeted using standard 1.8 x 9.1 m
Speeifie trapping loealities were seleeted in 2008 in mist nests set adjaeent to the Bone Cave opening in
an effort to maximize potential speeies diversity in area 3 and over water at the pond in area 1, or eaptured
building the referenee eolleetion within the limited time direetly with butterfly nets as the bats emerged from
period available for field work. Colleetion protoeols Bone Cave. Due to time eonstraints and a laek of
followed standard methods for eondueting biologieal aeoustie signals indieating the presenee of low-level
inventories for small mammals, and trapping efforts foraging bats, the other four areas were not sampled.
between years utilized similar numbers of traps set in
lines radiating out from GPS points reeorded in 2008. Trapping for earnivores eonsisted of setting Co-
nabear #220 body grip traps (Oneida Vietor, Cleveland,
Data eolleeted for eaeh trap line ineluded GPS OH) and 18 x 18 x 76 em Tomahawk live traps (Hazel-
positions of line starting and ending points, number and hurst, WI) in suitable habitats. Unbaited Conabear traps
type of traps set, and eapture sueeess. All field work were set direetly in burrow openings of springhares
was eondueted under Sam Houston State University (Pedetes capensis) in efforts to eapture them entering
lACUC permit #08-04-03-1005-3-01 issued to M. or leaving their burrow system, or to eapture assoeiated
L. Thies and guidelines of the Ameriean Soeiety of predators sueh as honey badgers (Melivora capensis).
Mammalogists for the use of wild mammals in researeh Tomahawk traps were baited with eanned eat food and
(Sikes et al. 2011). Eaeh small mammal eolleeted was sardines and plaeed in areas with deadfall and extensive
saerifieed by thoraeie eompression or over-anesthetized ground eover for small earnivores. Traps generally
with halothane, evaluated for general body eondition, were set in the evening and eheeked in the morning and
and standard museum speeimen data reeorded that evening of subsequent days until a eapture was made.
ineluded speeies, sex, weight, body measurements, Bait was replaeed as neeessary and the traps reloeated
and general eondition. A series of speeimens were to different habitats onee a eapture at a site was made.
prepared as standard museum skins and skeletons, All eaptures were proeessed in the same manner as
with the remaining speeimens preserved in formalin, speeimens eaptured with Sherman traps.
and deposited in the The Museum of Texas Teeh Uni¬
6 Occasional Papers, Museum of Texas Tech University
Figure 3. Photographs of representative habitats within the six Koanaka Hills trapping localities.
To aid in accurate species determination, all not sampled consistently and effectively between years,
retained specimens were definitively identified using those data were removed and species richness, diver¬
400 bp cytochrome-b sequences following protocols sity, abundance, and distributional patterns reexamined
outlined in McDonough et al. (2011). Collection data using both abundance and incidence based methods.
were used to determine species richness, diversity, rela¬
tive abundance, and distribution patterns for all species The date and source of ignition for the fire are not
collected within the areas surrounding Bone Cave and known, nor are other parameters such as fuel load, rate
the Koanaka Hills. Because bats and carnivores were of spread, extinguishing method, and total area burned.
Tries and Lewis—Effects of Fire on Small Mammals in Botswana 7
However, it is known that this was one of a number of speeies as eommon ones. The right-hand tail gives
fires that typieally oeeur during the months of August information about dominanee and eommon speeies:
through November that represent the peak of the dry when alpha is large, diversity is only slightly affeeted
season, many of whieh are ignited by lightning. by rare speeies (Leinster and Cobbold 2012). Due to
our relatively small sample sizes and probable trap¬
Data were analyzed for abundanee-based dif- ping biases, ineidenee-based eomparisons were made
ferenees using the program PAST and for ineidenee- using the non-parametrie Ineidenee-based Coverage
based differenees using Estimates v. 9 (Colwell 2013). Estimator (ICE) and Chao-2 riehness estimator values.
Shannon and Simpson indiees were ealeulated using Chazdon et al. (1998) reported that the ICE estimator,
abundanee data, with signifieanee of results of the ealeulated using both rare and eommon speeies, best
Simpson Indiees eompared within sites aeross years satisfies the requirements for an ideal speeies riehness
using a t-test. Diversities in abundanee data also were estimator and that Chao 2 also was relatively insensitive
eompared between years for eaeh area by plotting to sample size. Colwell and Coddington (1994) also
diversity against an index of sensitivity (Fig. 4). The showed that Chao 2 provided the least biased estimates
left-hand end of the diversity profile gives information for small numbers of samples and takes into aeeount
about speeies riehness and rare speeies: when alpha rare speeies and the total number of speeies observed
is small, diversity is afifeeted almost as mueh by rare in the sample to ealeulate its riehness.
Results
Trapping results and observational reeords were of rodent speeies were represented in both sampling
eompared for the six primary eolleetion areas estab¬ years (Aethomys chrysophilus: 2008 N = 19,2009 N =
lished from initial visual inspeetion of general fioral 112; Gerbilliscus brantsii: 2008 N = 21, 2009 N = 41;
eomponents and soil strueture (see Fig. 3 for repre¬ G. leucogaster: 2008 N = 23,2009 N = 43; Gerbillurus
sentative habitat images). A total of 25 small mammal paeba: 2008 N = 9,2009 N = 22; Lemniscomys rosalia:
speeies representing five orders (one Sorieomorpha, 2008 N = 1,2009 N = 5; Mastomys natalensis: 2008 N
five Chiroptera, 14 Rodentia, one Maero seel idea, and = 57, 2009 N = 72; Micaelamys namaquensis: 2008 N
four Carnivora) were eolleeted in the eourse of this = 24, 2009 N = 18; Mus minutoides: 2008 N = 1, 2009
study (Table 1). A single shrew speeies was eaught in N = 4; Saccostomus campestris: 2008 N = 6, 2009 N
both years (C. hirta\ 2008 N = 6, 2009 N = 4), as was = 2; Zelotomys woosnami: 2008 N = 1, 2009 N = 1).
a single speeies of elephant shrew {Elephantulus intufi\ However, three speeies {Cryptomys damarensis: N =
2008 N = 12,2009 N = 17). Five speeies of Chiroptera 2, Dendromus melanotis: N = 2, mdXerus inauris: N
(Chaerephon nigeriae: N = 1; Hipposideros commer- = 2) were only eaptured in 2008 and two speeies {Mus
sonr. N = 8; Neoromycia capensis: N = 10; Nycteris indutus: N = 6, and Steotomysparvus: N = 1) were only
thebaica: N = 12; Rhrynolophus dentr. N = 7) were eaptured in 2009 (Table 1).
eaptured in 2008; however, only three speeies {Hip¬
posideros commersoni: N = 1; Nycteris thebaica: N = Due to a laek of sufifieient proeessing time and
13; Rhynolophus denti: N = 13) were eaptured again resourees, and beeause the foeus of our work in 2008
in 2009, all obtained from either inside Bone Cave was to build a set of voueher speeimens for fossil iden-
or immediately outside its entranee in area 3. Only tifieation and a series of 10-12 members of a speeies
one speeies of small eamivore was trapped in 2008 was thought to be sufifieient, a small number of eaptures
{Galerella sanguinea: N=3), primarily as a result of were released during the 2008 field efforts. Adequate
a redueed effort for these taxa in 2008, whereas four reeords were not kept regarding speeies, numbers of
speeies were eaptured in 2009 {Cynictispenicillata: N individuals released, or areas where those released
= 1; G. sanguinea: N = 6; Genetta genetta: N = 1; M speeimens were eaptured, but we do know that only A.
capensis: N = 2) when signifieantly more effort was ap¬ chrysophilus, M. natalensis, and M. namaquensis were
plied to eatehing the smaller earnivores. The majority released: all other eaptures were retained and proeessed
8 Occasional Papers, Museum of Texas Tech University
Area 1 a b
- 1-2008 - 1-2008
- 1-2009 - 1-2009
Area 2 a b
-2-2008 -2-2008
-2-2009 -2-2009
b
Area 3 a
-3-2008 - 3-2008
-3-2009 -3-2009
alpha alpha
Figure 4. Diversity plots for the six Koanaka Hills study areas: a) plots with all data
included; and b) plots with bats and small carnivores excluded. The left side of each plot
provides comparative information on species richness and numbers of rare species and the
right side provides information on species dominance and common species.
Tries and Lewis—Effects of Fire on Small Mammals in Botswana
Area 4 a
- 4-2008 - 4-2008
- 4-2009 - 4-2009
Area 5 a
-5-2008 - 5-2008
-5-2009 - 5-2009
Area 6 a
-6-2008 - 6-2008
-6-2009 - 6-2009
alpha
Figure 4. (cont.)
10 Occasional Papers, Museum of Texas Tech University
9
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Table 1. Small mammal taxa Soricomorpha (shrews) Crocidura hirta UHcOUdhh -s.bssO:;o ^.KOoI1 ^•&S ^cij II"•SOS’; TTaOOa(OU33J ^^1o5I:^ obSs IqoIs; ~^s5!£3<b: 5I^ -O£Sbh ^bloI3. I^bs&gOs; ^•5is&2 1^ ^ss: CIQO CI0SSO3h Xerus inauris Zelotomys woosnami Macroscelidea (elephant shrew Elephantidus intufi