Effects of prescribed fire on an ant community in Floridapine savanna

IDO IZHAKI , DOUGLAS J . LEVEY and WESLEY R . S ILVA 1Department of

Zoology, University of Florida, U.S.A.

Abstract. 1. The effects of prescribed fire on ant community structure wereexamined in a regenerating longleaf pine savanna in Florida, U.S.A. The presenceof ants on 20, 10� 10m plots was determined by baiting every 1–3months from18months before a fire until 6months afterwards.2. Expected species richness (based on rarefaction) and species density 6months

post-fire were significantly lower than for the same month (September) 6monthsbefore the fire.3. Cluster analysis revealed that the effects of fire were far less important

predictors of ant community structure than seasonality and unexplained inter-annual variation. Thus, overall, the impacts of fire were relatively minor and shortterm at the community level.4. Different functional groups of ants (as defined by Andersen, 1997) responded

to fire in strikingly different ways. Generalised Myrmicinae (e.g. Pheidole spp.,Monomorium viride) were affected more severely by fire than were the otherfunctional groups. In contrast, the dominant Dolichoderinae (Forelius pruinosus)exhibited a large increase after the fire and seemed to be responsible for the declinein abundance of several species.5. A strong negative correlation between F. pruinosus and other groups of ants

immediately after the fire suggested more intense competition among ants at thattime. Six months post-fire, the abundance of F. pruinosus decreased markedly andthe abundance of other species rebounded.6. The rapid post-fire recovery of the ant community probably reflects adapta-

tions of ants to a chronic fire regime.

Keywords. Ant community, fire, functional groups, longleaf pine, speciesdensity, species richness.

Introduction

Longleaf pine Pinus palustris forests, which once dominated

the coastal plain of the south-eastern United States (Ware

et al., 1993), remain on <3% of their 30million ha historical

range (Frost, 1993; Landers et al., 1995). Because these

forests are among the most species-rich plant communities

outside the tropics (Peet & Allard, 1993) and among the

most threatened ecosystems in North America (Simberloff,

1993; Stout & Marion, 1993; Noss et al., 1995), restoration

efforts are widespread. Restoration, however, is a lengthy

process and large areas are in transitional habitat. Ideally,

management and restoration of these areas are based on an

understanding of the dynamics of the entire community, not

simply the dominant species of plant. Relatively little is

known about the fauna of longleaf pine forests, especially

invertebrates (Folkerts et al., 1993). Only a handful of studies

has examined the species composition and community

dynamics of ants in these forests (Van Pelt, 1956, 1958;

Campbell, 1996; Prusak, 1997; Lubertazzi, 1999).

The work reported here was focused on the dynamics of

ant community structure in a high pine habitat (Myers,

1990) being managed for restoration of longleaf pine.

Correspondence: Ido Izhaki, Department of Biology, Faculty of

Science and Science Education, University of Haifa at Oranim,

Tivon 36006, Israel. E-mail: izhaki@research.haifa.ac.il1Current Address: Departamento de Zoologia, UNICAMP, 13083-

970 Campinas, Brazil.

Ecological Entomology (2003) 28, 439–448

# 2003 The Royal Entomological Society 439

As with any ant community, its structure and dynamics

depend primarily on disturbance, vegetation attributes,

and competitive interactions (Andersen, 1995). Before

European settlement, the main natural disturbance in long-

leaf pine ecosystemswas fire (Christensen, 1981, 1988;Robbins

& Myers, 1992; Ware et al., 1993). Now, fire is a primary

means of managing longleaf forests (Landers et al., 1995).

Although it is assumed widely that the flora and fauna of

longleaf pine ecosystems are highly adapted to frequent fires

(Wade et al., 2000), surprisingly little research backs this

assumption (Engstrom, 1993; Folkerts et al., 1993).

With respect to ants, post-fire recovery has been studied

in Australian eucalyptus forests (reviewed by Christensen &

Abbott, 1989), tropical dry and wet forests (Bentley,

1976; De Morais & Benson, 1988; Andersen, 1991; MacKay

et al., 1991), European boreal forest (Punttila & Haila,

1996), and coniferous forests (Pearse, 1943). Folgarait

(1998) reviewed the effect of different disturbances on ant

biodiversity and concluded that ant diversity generally

increases after fire; however ant diversity after fire may

also decrease (e.g. Majer, 1977; York, 2000) or remain

unchanged (e.g. Majer, 1977; Jackson & Fox, 1996),

depending on biotic and abiotic conditions and on the

time elapsed since fire.

Fire is not the only factor that may impose temporal

changes in ant communities. Natural seasonal cycles in abiotic

factors (such as moisture and temperature) and biotic factors

(such as vegetation cover) are likewise important (Holldobler

&Wilson, 1990). Although seasonal activity cycles in ants have

been documented (Lynch et al., 1980; Whitford et al., 1981;

Fellers, 1989; Suarez et al., 1998), studies on activity patterns

of entire ant assemblages that extend throughout the annual

cycle are less common (but see Fellers, 1989; Prusak, 1997;

Albercht & Gotelli, 2001).

In the work reported here, the short-term effect of fire on

the structure of a longleaf pine ant community was evaluated

by describing the seasonal activity pattern of ants foraging on

the forest floor 1.5years pre-fire to 0.5years post-fire. The com-

parison was based on species richness and on functional groups

that classify ants relative to their response to environmental

stress and competitive interactions (Andersen, 1995, 1997).

Study site

The study was carried out in the Katharine Ordway Preserve,

in the Interlachen Karstic Highland in north-east Florida

(29�410N, 82�000W). The area had an unnatural fire regime

(fire suppression) while it was used for agricultural practices

in the last half of the 19th and first half of the 20th Centuries

(Franz, 1991). Prescribed burning now occurs on a 3–5year

cycle. The site was burned 1 year before the study began. The

vegetative community is classified as sandhill high pine

(Myers, 1990); longleaf pines and turkey oak Quercus laevis

are common in the overstorey. The understorey is dominated

by wire grass Aristida stricta, pineywoods dropseed Sporo-

bolus junceus, and blue stem grasses Andropogon spp. Large

areas of bare soil are common.

Materials and methods

In June 1994, ten 10� 10-m plots were placed randomly in

each of two 200� 200-m study sites that were separated by

2 km. Ants were sampled on each plot with nine tuna baits

(� 10 g, oil packed) placed in a 3� 3-m grid. Tuna baits are

commonly used to sample ant communities and the

common species observed at tuna baits correspond closely

with the common species captured in pitfall traps (Andersen,

1992, 1997; Perfecto & Vandermeer, 2002). Observations

at baits are likely to over-inflate the apparent effects of

behaviourally dominant species but this does not necessarily

mean that they suppress the general foraging activity of the

subordinate ants (Andersen & Patel, 1994). After 30–60min,

ants were collected from on top of, underneath, and around

the baits. Pilot trials confirmed that this sampling period

ensured that baits were found frequently by more than one

species and typically not dominated by any one of them.

Indeed, many non-dominant species were detected. The ant

fauna was sampled every 1–3months between September

1994 and September 1996, always in the morning when

the temperatures were relatively mild and it was not raining.

A total of 1962 ant samples per bait was collected in

11 baiting sessions and preserved in 95% alcohol for later

identification. In February 1996, a low-intensity fire was set

on both sites.

Species density was calculated as the total number of

species sampled in each plot. Because estimates of species

richness can be biased by differences in numbers of

individuals sampled, which can reflect differences in

environmental conditions rather than underlying differ-

ences in ant community composition, expected species rich-

ness was calculated by rarefaction (McCabe & Gotelli,

2000; Gotelli & Colwell, 2001). Rarefaction eliminates vari-

ation in species richness due to differences in sample size

(number of ant species captured in each plot) by resampling

a pool of N individuals repeatedly at random (Gotelli &

Colwell, 2001). Rarefaction was used to estimate expected

species richness in each baiting session per plot, using

n¼ 12 to represent the lowest number of individual ant

species at a bait trapped per plot. Rarefaction was also used

to calculate the expected species richness inall plots combined

in May 1995 (before the fire), May 1996 (after the fire),

and in September 1994, 1995 (before the fire), and 1996

(after the fire). In these pooled analyses, n¼ 222 was used to

compare the two May values and n¼ 255 to compare

the three September values. These sample sizes are the

highest shared among the months in different years. Cal-

culations were made by the Rarefaction Calculator (http://

www.biology.ualberta.ca/jbrzusto/rarefact.php), based on

theoriginalmethodproposedbySanders (1968)andmodified

by Hurlbert (1971) and Simberloff (1972).

The frequency of occurrence of ants per plot was calcu-

lated as the total number of baits on which a species or a

functional group was detected (see below). For example, in

the case of a functional group that included five ant species,

the minimum frequency of occurrence per plot is 0 (no ant

from the group detected) and the maximum value is 45

440 Ido Izhaki, Douglas J. Levey and Wesley R. Silva

# 2003 The Royal Entomological Society, Ecological Entomology, 28, 439–448

(each of the five species detected on each of the nine baits).

This index assumes that abundant species will be found on

more tuna baits than will rare species.

To assess the similarity of ant assemblages pre- and post-

fire, values of frequency of occurrence for each species for

each baiting session were clustered using the single-linkage

nearest-neighbour method based on Euclidean distance

(Krebs, 1998). The frequency of occurrence was also used

to calculate pairwise Pearson correlations among the most

common functional groups to reveal associations between

ant groups pre- and post-fire. Partial correlation analysis

was used to remove the effect of the other functional groups

for each functional group pair.

All ant species were classified into functional groups.

These groups are based on ecological rather than taxonomic

criteria and follow a long tradition in community ecology of

comparing roles that species play in communities. A classi-

fication scheme based on habitat requirements and

competitive interactions that has been used extensively in

Australia and validated recently for North American ant

faunas was adopted (Andersen, 1997). The following

groups were present at the site: dominant Dolichoderinae

(species favouring hot, open areas and that are aggressive

and dominant); subordinate Camponotini (large species

that tend to forage at night and are submissive to the

previous group), hot climate specialists (species adapted to

arid conditions and that avoid dominant Dolichoderinae),

cold climate specialists (species typical of cooler conditions

and in areas with few dominant Dolichoderinae), tropical

climate specialists (species typical of warmer conditions and

in areas with few dominant Dolichoderinae), opportunists

(species that colonise disturbed areas rapidly and are weak

competitors), and generalised Myrmicinae (species that are

found in many habitats and that recruit to and defend

clumped resources quickly). Assignment to these groups was

based on genera, as suggested by Andersen (1997; Table 1).

Differences in species density, expected species richness,

and frequency of occurrence among the 11 baiting sessions

were assessed using a one-way ANOVA with month (time) as a

repeated measure. Tukey post-hoc tests were used to

compare differences among months. To deal with the diffi-

culty of zero values and stabilise the variance, one was

added to all values then the data were log transformed

(Zar, 1996). All statistical calculations were performed

using the Statistical Package for the Social Sciences version

9 (SPSS, 1996).

Results

Pre- and post-fire ant community composition

A total of 30 ant species was recorded (Table 1). Expected

species richness per plot was always lower than species

density per plot because the calculation of expected richness

is based on the lowest number of individual species (n¼ 12)

trapped per plot; however the pattern of both indices during

the study period was similar (Fig. 1). There were obvious

and significant differences in species density and expected

species richness per plot among the 11 baiting sessions

(P-values <0.001; Fig. 1). Before the burn, ant activity

showed a seasonal cycle, with high species density and

expected species richness in the autumn and low density

and richness in the winter (Fig. 1). Both species density

and species richness per plot peaked in September 1995.

Although both indices in September 1994 were relatively

high, they were significantly lower than in September 1995

(Tukey post-hoc tests, P< 0.05). Both indices in May 1995

(7months before the fire) were higher than in May 1996

(3months post-fire) but the differences were not significant

(Tukey post-hoc tests, P> 0.05), however both indices in

September 1995 (5months before the fire) were significantly

higher than in September 1996 (6months post-fire; Tukey

post-hoc tests, P< 0.05). The indices in September 1994

were not different from those after the burn in September

1996 (Tukey post-hoc tests, P< 0.05). Thus, the effect of fire

on species density and richness per plot depended on the

time-scale of the comparison; there was little immediate

effect (perhaps because ant populations were already

depressed by cool weather associated with the winter

burn) but a reduction evident 6months later. This reduction

Table 1. Classification of ant species collected at tuna baits in

north central Florida into functional groups (after Andersen,

1997). Species nomenclature follows Bolton (1995).

Functional group Ant species

Cold climate specialists Leptothorax spp. (two species)yPrenolepis impairs Say

Dominant Dolichoderinae Forelius pruinosus Roger

Generalised Myrmicinae Crematogaster ashmeadi Mayr

Monomorium viride Brown

Pheidole dentate Mayr

Pheidole floridana Emery

Pheidole morrisi Forel

Pheidole spp. (three species)zHot climate specialists Pogonomyrmex badius Latreille

Solenopsis geminata Fabricius

Opportunists Aphenogaster spp. (two species)§

Dorymyrmex bossuta Trager

Dorymyrmex bureni Trager

Dorymyrmex grandula Forel

Odontomachus brunneus Patton

Paratrechina arenivage Wheeler

Paratrechina parvula Mayr

Formica archboldi Smith

Formica pallidefulva Latreille

Subordinate Camponotini Camponotus floridanus Buckley

Camponotus nearcticus Emery

Camponotus socius Roger

Tropical climate specialists Pseudomyrmex sp.

Trachymyrmex septentrionalis

McCook

Cyphomyrmex rimosus Spinola

yL. pergandei Emery and L. texanus Wheeler.

zP. adrianoi Naves, P. littoralis Cole, and P.metallescens Emery.

§A. floridana Smith and A. flemingi Smith.

Effects of prescribed fire on an ant community 441

# 2003 The Royal Entomological Society, Ecological Entomology, 28, 439–448

was not apparent when compared with data collected

18months before the burn.

Pooling across all plots (rather than averaging, as above)

allows comparison of the rarefaction curves based on large

sample sizes for months in which ants were sampled both

before and after the burn (May 1995 vs 1996 and September

1994 and 1995 vs 1996). The expected species richness curve

in May 1995 (before the fire) was higher and steeper than in

May 1996 (post-fire; Fig. 2). Because in May 1996 a smaller

number of ants was collected on tuna baits (n¼ 222), the

curves for the 2 years must be compared by moving

vertically from n¼ 222 individuals on the x-axis until the

curves are intercepted. Doing so revealed that in May 1995

species richness was 33% higher than in May 1996 (20 vs 15

species) and that the error bars did not overlap, indicating

that the difference was significant. Likewise, comparison of

the rarefaction curves from September 1994, 1995, and 1996

revealed that although the expected species richness

6months after the fire (September 1996) was lower than

6months before the fire (September 1995), it was higher

1.5 years before the fire (September 1994). For n¼ 225 (the

lowest value, September 1994), species richness in September

1996 was 12% lower than in September 1995 (19.5 vs

22.2 species) but 15% higher than in September 1994 (17

species). In summary, these results indicate that species

richness fell immediately after the fire (in May 1996) and

remained depressed for at least 6months (September 1996),

compared with levels 6months before the fire (September

1995); however species richness was much lower 18months

before the fire (September 1994) than 6months afterwards

(September 1996), indicating a large degree of annual

variation presumably independent of the fire regime.

The cluster analysis revealed three groups, clearly reflect-

ing seasonal shifts in ant community composition (Fig. 3).

The largest group included all baiting sessions that occurred

01

23

45

67

89

Spe

cies

den

sity

Fire

BCD

D CDCD

A

B

CD CD

B

D

BC

F P10,190 = 6.81, < 0.001

0123456789

Sep. Nov. Jan. Mar. May Jul. Sep. Nov. Jan. Mar. May Jul. Sep.

Date

Exp

ecte

d sp

ecie

s ric

hnes

s

199619951994

Fire

A

CC C

CBBC BC BC

BCB

F P10,190 = 4.11, < 0.001

Fig. 1. Ant species density (number of species per plot) and

expected species richness per plot for the same data calculated by

rarefaction (assuming n¼ 12 individuals per plot). Bars labelled

with the same letter are not significantly different (Tukey post-hoc

test, P >0.05). Data are meansþ 1 SE. n¼ 20 plots.

0

5

10

15

20

25

Exp

ecte

d sp

ecie

s r ic

hnes

s

1996

1995

May

0

5

10

15

20

25

0 100 200 300 400

Number of individuals

Exp

ecte

d sp

ecie

s r ic

hnes

s

1994

1996

1995September

Fig. 2. Rarefaction curves based on pooled data from all plots in

May and in September before the fire (dashed lines and open

circles) and post-fire (solid lines and filled circles). The curves show

expected species richness of ants for a given number of randomly

sampled individuals. Data are means� 1 SD.

442 Ido Izhaki, Douglas J. Levey and Wesley R. Silva

# 2003 The Royal Entomological Society, Ecological Entomology, 28, 439–448

in the spring and summer and two autumn samples (Sep-

tember 1994 and 1995). The two other groups comprised

autumn (November and September) and winter (December

and February) samples. Because these major groups were

defined by season, not by whether samples were collected

pre- or post-fire, the cluster analysis suggested that season-

ality had a stronger influence on ant community structure

than did fire. Indeed, the first three post-fire sessions

(March, May, July 1996) clustered together with three

pre-fire sessions (May 1995, September 1994, September

1995), and the last post-fire baiting session (September

1996) clustered together with November 1995 (Fig. 3).

Functional groups

The two richest functional groups in the samples were

opportunists (10 species in Dorymyrmex, Paratrechina,

Formica, and Odontomachus) and generalised Myrmicinae

(eight species in Pheidole, Crematogaster, and Monomor-

ium) (Table 1). Cold climate specialists, tropical climate

specialists, and subordinate Camponotini each included

three species (of Leptothorax and Prenolepis for the former,

Camponotus for the latter). Hot climate specialists

comprised two species (of Pogonomyrmex and Solenopsis).

The remaining functional group, dominant Dolichoderinae,

was represented by a single species (of Forelius).

In terms of frequency of occurrence (the number of tuna

baits in each plot that attracted species in each functional

group), generalised Myrmicinae were most common,

followed closely by opportunists and dominant Dolichoder-

inae. Hot climate specialists, cold climate specialists, and

subordinate Camponotini were uncommon; tropical climate

specialists were rare (Figs 4 and 5).

The six most common functional groups displayed sig-

nificant variation in abundance among the 11 baiting

sessions (Fig. 4). The general pre-fire seasonal pattern of

species density and expected richness observed for all ant

species (Fig. 1) also held for ant abundance of several func-

tional groups (e.g. opportunists, hot climate specialists) but

not for others (e.g. cold climate specialists, dominant

Dolichoderinae; Fig. 4). The maximal abundance of cold

climate specialists was observed in winter (February 1996).

In contrast, dominant Dolichoderinae were rare in winter

and relatively common in spring and autumn.

Comparing abundances in the same months pre- and

post-fire, only generalised Myrmicinae abundance was

significantly lower in May 1996, 3months post-fire, than

in May 1995 (before the fire; Fig. 4). Although this group

was similar in abundance to dominant Dolichoderinae

before the fire in May 1995, its abundance was signifi-

cantly lower than that of the dominant Dolichoderinae

after the fire (Fig. 5; see figure caption for results of

statistical tests). Only dominant Dolichoderinae were

significantly less abundant in September 1996, 6months

post-fire, than in September 1995, before the fire (Fig. 4).

Dominant Dolichoderinae were significantly more

abundant than any other functional group in September

1994 before the fire but significantly less abundant than

generalised Myrmicinae and opportunists in September

1996, after the fire (Fig. 5), however this group was also

significantly less abundant than the generalised Myrmici-

nae in September 1995 before the fire (Fig. 5). Dominant

Dolichoderinae displayed one additional and unique pat-

tern: they increased in abundance significantly between

February and March 1996, just before and just after the

fire (Fig. 4). No other group increased in abundance

immediately after the fire, however there was a significant

increase in hot climate specialists 5–7months post-fire

(July and September 1996; Fig. 4). For all other functional

groups, there were no significant differences in ant

abundance pre- and post-fire in parallel months (Fig. 4),

and there were no differences in their abundance relative

to other groups before and after the fire (Fig. 5).

Pairwise correlations among functional groups were

restricted to the three Septembers, two before fire (1994

and 1995) and one post-fire (1996), and the two Mays, one

before the fire (1995) and one post-fire (1996). Using partial

correlations to remove the effects of the other functional

groups, there was a significant negative correlation between

abundance of dominant Dolichoderinae (Forelius pruinosus)

and generalised Myrmicinae. This relationship was consist-

ent in all five sampling periods, both pre- and post-fire

(Table 2) and was stronger in September after the fire than

in the two Septembers pre-fire (P< 0.01 vs P< 0.05). It was

even more apparent in the samples from the two Mays

(P< 0.001). A strong negative correlation was also evident

between dominant Dolichoderinae and opportunists,

although only in September 1996 (P< 0.01; Table 2).

Finally, abundances of generalised Myrmicinae and hot

climate specialists were correlated significantly and posi-

tively in May 1996 (Table 2).

May 95

Mar. 96

Sep. 94

Jul. 96

May 96

Sep. 95

Nov. 95

Sep. 96

Dec. 94

Feb. 95

Feb. 960 Euclidean distance 25

Fig. 3. Dendrogram from a cluster analyses (using nearest-

neighbour method) of ant community structure across all baiting

sessions. Pre-fire sessions are in normal font; post-fire sessions are

in bold.

Effects of prescribed fire on an ant community 443

# 2003 The Royal Entomological Society, Ecological Entomology, 28, 439–448

Discussion

The results suggest that low-intensity fire in longleaf pine

forest in winter (February) has a negative but short-term

effect on the ant community. Although only 3months after

the fire (May 1996), per plot estimates of species density and

expected richness were similar to those in May 1995 before

the fire, the analysis on pooled plots revealed significantly

higher expected species richness before the fire. Both pooled

and per plot analyses showed that expected species richness

in September 1996 (6months post-fire) was still below the

pre-fire values in September 1995 but not significantly

different from the values in September 1994, 1.5 years

pre-fire. Based on the differences in species richness that

were recorded between two pre-fire Septembers (1994 and

1995), however, the differences in species richness that were

recorded between September 1996 (post-fire) and September

1995 (pre-fire) may not be attributed solely to fire.

The negative effect of fire on ant community structure

was probably not due to mortality caused directly by the

fire itself because most ants probably found refuge in their

underground nests (Andersen & Yen, 1985). Rather, the

reduction in general species richness after the fire may have

been caused by the destruction of understorey vegetation and

the subsequent impact on arthropod food sources (New

& Hanula, 1998). Alternatively, the loss of vegetation may

have affected ants more directly by reducing or eliminating

essential microhabitats (Andersen, 1991; Folkerts et al.,

1993) or by having a negative impact on below-ground

microclimate (Heyward & Tissot, 1936).

A rapid overall post-fire recovery rate of ants was evident

from the pronounced lower differences (12%) in species

richness in pooled data between September 1996 (6months

after fire) and September 1995 (before the fire) relative to

the high differences (33%) in species richness between May

1996 (3months after fire) and May 1995 (before the fire).

The cluster analysis also revealed rapid post-fire recovery of

the ant community. In particular, ant assemblages in the

first three post-fire baiting sessions were relatively similar,

but the assemblage in the last baiting session, 6months

post-fire (September 1996), was similar to several pre-fire

ant assemblages (Fig. 3b). More generally, the cluster

0123456789

FireA

ABC

F

Generalised MyrmicinaeF10,190 = 7.37, P < 0.001

BCCDBCD CD

DEDEF

EF

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Fire

0.00.20.40.60.81.01.21.41.61.8

Sep.Nov.Jan. Mar. May Jul. Sep.Nov.Jan. Mar. May Jul. Sep.

Date

199619951994

Sep.Nov.Jan. Mar. May Jul. Sep.Nov.Jan. Mar. May Jul. Sep.

Date

199619951994

Fire

0

1

2

3

4

5

6

7

Fire

0

1

2

3

4

5

6

7

Fire

0.0

0.5

1.0

1.5

2.0

2.5

Fire

D

BCD

A

D

B

CD

ABAB

A

C C

AB

D

FG

AA

EF

AB

AAB

AB

ABCABC

A

BCD

Hot climate specialistsF10,190 = 2.87, P < 0.01Subordinate Camponotini

F10,190 = 3.96, P < 0.001

Dominant DolichoderinaeF10,190 = 16.04, P < 0.001

Cold climate specialistsF10,190 = 7.28, P < 0.001

OpportunistsF10,190 = 8.39, P < 0.001

ABC

CDBCD

DE DEFEF

CDCDBCD

AB

DD

BCD BCDBCD

BC BCCD

ABB

D

D

D

E

BC BC C

A

C

B

Ant

freq

uenc

y of

occ

urre

nce

per

plot

Fig. 4. Frequency of occurrence (meanþ 1SE) of the six most common functional groups of ants before and after the fire. Differences among

months were tested by repeated-measures ANOVA. Bars labelled with the same letter are not significantly different (Tukey post-hoc test, P¼NS).

444 Ido Izhaki, Douglas J. Levey and Wesley R. Silva

# 2003 The Royal Entomological Society, Ecological Entomology, 28, 439–448

analysis revealed a much stronger influence of season than

fire on ant community composition.

These results match conclusions from previous studies.

Ants appear to recover rapidly from a wide variety of dis-

turbances (Folgarait, 1998). For example, most ant species

recolonised within 1 year after fire in an Australian forest

(Neumann, 1991). The rapid recovery at the site is probably

related to the fact that fire is an integral part of longleaf

pine forests (Wade et al., 2000). Thus, ants are probably

adapted to the fire regime; they can avoid direct mortality

by the fire and can take advantage of prevailing conditions

immediately after the fire (Andersen & Yen, 1985;

Andersen, 1991).

Impact of fire on functional groups

The immediate post-fire response of generalised Myrmi-

cinae was more pronounced than that of the other

functional groups. Thus, this group’s response may have

been largely responsible for the community-wide reduction

in species density and richness after the fire.

Why were generalised Myrmicinae affected markedly by

fire? Because members of this group (Pheidole spp. and

Monomorium viride) are dietary generalists, they are

presumably able to adapt their foraging behaviour better

to new conditions than would ants in many of the other

functional groups. The surface fire probably did not

damage their nests more severely than nests of the other

functional groups. Furthermore, the prescribed fire created

considerable patches of bare ground, which are favourable

to generalised Myrmicinae (Andersen, 1991), however

patches of bare ground are also favourable to the behaviour-

ally dominant Forelius pruinosus (dominant Dolichoderi-

nae; Andersen, 1995), which had a massive presence

immediately after the fire. The strong negative correlations

detected between abundances of dominant Dolichoderinae

Table 2. Partial correlation analysis of the five most common functional groups of ant. Species in each group are listed in Table 1. Partial

correlation coefficients between each functional group measured in three Septembers are above the diagonal (1994 and 1995 pre-fire; 1996

post-fire in bold) and in two Mays are below the diagonal (1995 pre-fire; 1996 post-fire in bold). For each pair of functional groups,

abundances of all other groups were factored out. n¼ 20 plots.

Dominant

Dolichoderinae

Generalised

Myrmicinae

Hot climate

specialists Opportunists

Subordinate

Camponotini

Dominant Dolichoderinae �0.60* �0.08 0.30 0.14

�0.49* 0.21 �0.03 0.09

�0.66** 0.23 �0.72** �0.35

Generalised Myrmicinae �0.77*** �0.02 0.31 0.06

�0.77*** �0.20

�0.05

0.02

�0.44

�0.25

�0.06

Hot climate specialists 0.42 0.54* �0.15 �0.32

�0.06 �0.18 �0.003

�0.04

�0.31

0.04

Opportunists �0.15 0.15 0.14 �0.08

�0.02 0.12 0.08 �0.28

�0.29

Subordinate Camponotini �0.06 0.12 �0.15 �0.28

�0.12 0.15 0.02 �0.17

*P< 0.05, **0.001<P< 0.01, ***P< 0.001.

0

2

4

6

8

Generalised Myrmicinae Opportunists

Dominant Dolichoderinae Subordinate Camponotini

Cold climate specialists Hot climate specialists

May

AA

BB B B

A

BC

D D DC

012345678

1994 1995 1996

September

Pre-fire Post-fire

AB B

C C C

A

BB

CC

C

A A

B

BCC

C

Ant

freq

uenc

y o f

occ

urre

nce

Fig. 5. Frequency of occurrence (meanþ 1 SE) of the six most

common functional groups in May and September before (1994,

1995) and after (1996) a fire. Differences among functional groups

within each session were analysed for all eight functional groups

and found to be significant for all baiting sessions (one-way ANOVA,

May 1995: F¼ 37.1, d.f.¼ 7,152, P< 0.001; May 1996: F¼ 30.2,

d.f.¼ 7,152, P< 0.001; September 1994: F¼ 21.3, d.f.¼ 7,152,

P< 0.001; September 1995: F¼ 23.0, d.f.¼ 7,152, P< 0.001;

September 1996: F¼ 18.2, d.f.¼ 7,152, P< 0.001). Bars labelled

with the same letter are not significantly different (Tukey post-hoc

test, P¼NS).

Effects of prescribed fire on an ant community 445

# 2003 The Royal Entomological Society, Ecological Entomology, 28, 439–448

and generalised Myrmicinae suggest a competitive inter-

action in which Forelius pruinosus thrived in post-fire

conditions and excluded species of generalised Myrmicinae.

A similar situation occurs in savanna forests of Australia,

where a dominant species (Iridomyrmex) is abundant

immediately after fires and generalised Myrmicinae are

unusually rare (Andersen, 1991, 1992). Such interpretation

is also supported by the fact that the increased post-fire

abundance of generalised Myrmicinae between May and

September 1996 parallelled a significant decrease in the

abundance of the dominant Dolichoderinae (Fig. 4) and

may be interpreted as competition release (Vanerwoude

et al., 1997). The decrease in dominant Dolichoderinae

6months post-fire may have been caused by massive seed

germination and the reduction in bare ground that

followed, as this group is commonly absent from heavily

shaded habitats (Andersen & Majer, 1991; Andersen &

Reichel, 1994).

The effects of F. pruinosus on other functional groups

immediately after the fire were not restricted to generalised

Myrmicinae. There was also a significant negative post-

fire association with opportunists in September 1996, but

not in the two Septembers before the burn. A functional

group model predicts that generalised Myrmicinae and

opportunists are the most sensitive to competition from

dominant Dolichoderinae (Andersen, 1995). The ability of

F. pruinosus to maintain its dominance during the first

3 post-fire months contradicts findings from Australia,

where fire created a more equitable distribution of ant

functional groups compared with pre-fire communities

(Andersen & Yen, 1985; Vanerwoude et al., 1997).

Conclusions

In fire-adapted habitats, fire is generally thought to be

beneficial for ants because it increases plant growth and

seed production, mobilises nutrients, and clears obstruc-

tions to foraging (Springett, 1976; Whelan et al., 1980;

O’Dowd & Gill, 1984; Andersen & Yen, 1985; Andersen,

1988; Neumann, 1991, 1992; Jackson & Fox, 1996). In

longleaf pine forests, Folkerts et al. (1993) concluded that

frequent fires increase arthropod diversity because they

increases the biomass and species richness of herbs

(Gates & Tanner, 1988), however no positive effect of fire

on ant species richness was found within the first 6months

post-fire. On the contrary, species richness was initially

depressed by the fire, a result probably caused by the sud-

den dominance of a single species (F. pruinosus). It should

be emphasised, however, that the ant community recovered

quickly as vegetation re-established. Thus, the negative

impact of the burn was temporary.

Longer-term impacts of fire regime on ant communities

remain largely unexplored. Furthermore, there is little

recognition that variation in fire frequency, season, and

intensity are likely to affect ants in different ways

(Andersen, 1991). Understanding such responses has

general implications. Because ants are relatively easy to

study and are associated tightly with soil and ground-level

vegetation, they may prove to be valuable bio-indicators of

ecosystem disturbance. Majer (1983), for example,

concluded that responses of ants to disturbance mirror

responses of other arthropods. If this relationship holds

true in longleaf pine forests, it will greatly facilitate manage-

ment and restoration efforts aimed at the entire community.

Acknowledgements

Ido Izhaki was supported through sabbatical leaves from

the University of Haifa at Oranim. Wesley Silva was

supported in Florida by a grant of CAPES. John Eisenberg

and Mel Sunquist provided logistical support at the

Ordway Preserve. Lloyd Davis, Mark Deyrup, Bert

Holldobler, Cliff Johnson, and Sanford Porter provided

valuable advice on the taxonomy and natural history of the

ant fauna.

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Accepted 31 March 2003

448 Ido Izhaki, Douglas J. Levey and Wesley R. Silva

# 2003 The Royal Entomological Society, Ecological Entomology, 28, 439–448