Download Impact of argentine ants (Linepithema humile, Mayr) on saproxylic

Impact of Argentine ants (Linepithema humile Mayr) on saproxylic invertebrates in
Afromontane forest and pine plantation of the Cape Peninsula (South Africa)
Dimby Raharinjanahary
Percy FitzPatrick Institute, University of Cape Town
Rondebosch 7701, South Africa
Supervisor: Dr. M. D. Picker
Project submitted in partial fulfillment of the requirements for the degree of Master of Science
in Conservation Biology, University of Cape Town
February 2007
Format: Conservation Biology
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The copyright of this thesis rests with the University of Cape Town. No
quotation from it or information derived from it is to be published
without full acknowledgement of the source. The thesis is to be used
for private study or non-commercial research purposes only.
ABSTRACT
Saproxylic species are major contributors in the biodiversity of any natural forest. The impact
of the invasive Argentine ants (Linepithema humile) on the macroinvertebrate saproxylic
fauna was examined in rotting deadwood in undisturbed and pine supplanted forests on Table
Mountain (Cape Peninsula, South Africa). Argentine ants were found in both pine forest and
low altitude regions of the Afromontane forest. In total, 155 morphospecies have been
recorded comprising five phyla: Platyhelminthes, Annelida, Mollusca, Onychophora and
Arthropoda. Among them, nine Cape Peninsula endemic species have been found mostly in
Afromontane forest. Estimated species richness of the saproxylic communities in pine
plantations was 2.2 times less than that of Afromontane forest. Invaded and uninvaded
Afromontane forest had significantly different species assemblages. Invaded forest has 96
observed species whereas uninvaded one has 81 species, suggesting that Argentine ants do not
have a marked negative impact on xylophagous and xylomycophagous communities in the
studied habitat. Similarly, native ant species living in rotten logs were not affected by
Argentine ants. However, other 15 introduced alien saproxylic species were also found in all
study sites confusing the real impact of the Argentine ant.
Keywords: saproxylic, pine plantation, Afromontane forest, Linepithema humile, Argentine
ants, invasive species, Gondwanan relicts, Cape Peninsula.
INTRODUCTION
Saproxylics comprize the community dependent on dead or dying wood, wood-inhabiting
fungi, or the presence of other saproxylics (Speight 1989), and range from fungi through to
vertebrates (Dudley & Vallauri 2004). Their impressive diversity is explained by the
successional stages in the decomposition of wood (Dudley & Vallauri 2004). Wood-feeding
beetles and fungi initiate the decaying process of the wood, which then attracts many larval
and adult trophic guilds of different invertebrate groups (Key 1993; Grove 2002).
The saproxylic invertebrate fauna accounts for a large proportion of the species richness in
any natural forest (Grove 2002). Elton (1966) recorded 456 species of invertebrates from dead
wood habitats in a single British woodland, and Köhler (2000) working in a European forest
considered 56% of all forest beetles in that region as saproxylic.
In the Cape Peninsula of South Africa (a National Park afforded World Heritage Status), the
majority of the 111 local endemic invertebrates (Picker & Samways 1996) are associated with
refugial Afromontane forest growing on the eastern and southern slopes of Table Mountain.
The very high levels of Cape Peninsula endemism are probably due to vicariant speciation
following mid-Miocene and early Pleistocene flooding and isolation of the Cape Peninsula
(Hendey 1983). Regular cloud cover and orographic precipitation maintain high moisture
levels of the forest floor. This fauna has a strong Gondwanan signature, and currently survives
in temperate and moist refugial habitats, following the gradual warming and aridification of
Africa as it moved northwards after continental breakup during the Cretaceous (EndrödyYounga 1988). Moist rotting logs offer additional stability in terms of maintaining high
moisture levels.
Vicariant speciation resulting from flooding in the mid-Miocene and early Pleistocene
(Hendey 1983) was probably responsible for the very high levels of Cape Peninsula
endemism (Picker & Samways 1996).
Very little ecological work has been done on the saproxylic fauna of the South African
forests, apart from some basic ecophysiological studies that focused on the physiological and
behavioural adaptations of animals to life in this ‘cryptic’ habitat (Lawrence 1953) and the
impact of removing fuelwood on cavity-nesting birds and mammals (Du Plessis 1995).
The collection and removal of deadwood, for domestic fuel or for aesthetic reasons (by park
managers) are major threats to saproxylic communities. Although these practices do not take
place in the Cape Peninsula, past and current human activities have produced a mosaic of
disturbed habitats embedded within undisturbed Afromontane forest. The major habitat
change has been the extensive supplantation of Afromontane forest with pine (Pinus radiata
and P. pinaster) and eucalyptus plantations. These alien forests would exclude most native
phytophagous insects (Fenner & Lee 2001; Tewksbury et al. 2002), but their impacts on the
endemic saproxylic fauna is poorly known. Samways et al. (1996) using pitfall traps in
KwaZulu-Natal (South Africa) found that species richness of invertebrates in pine and
eucalyptus plantations was somewhat lower than that of nearby native forests, but not
significantly so. However, Ratsirarson et al. (2002) (using a sifted litter technique) found that
in the Cape Peninsula the estimated number of species in Afromontane forest was 2.4 times
greater than in pine plantations. Alien plantations and associated disturbance cascades
promote the establishment of alien invertebrates (Samways et al. 1996; Lenz & Taylor 2001;
Costello et al. 2003;), which have the potential to displace native species through predation,
interference competition or indirect effects (Gambino et al. 1987; Johnson et al. 2005).
The alien invertebrate on the Cape Peninsula with the greatest potential for ecological
disruption is the Argentine ant (Linepithema humile Mayr)(Lach et al 2002). It reached the
Cape Peninsula by 1908 (Skaife 1955; Prins et al. 1990) and continues its spread in South
Africa. In terms of impacts on other species, Skaife (1962) reported that all other native ants
were either killed or displaced by established Argentine ants. In undisturbed Fynbos
vegetation of the Western Cape Province (South Africa), Donnelly and Giliomee (1985)
reported low native ant species diversity in invaded Mountain Fynbos sites compared to
uninvaded control sites. Similarly, Slingsby (1982) showed that the Argentine ant had
eliminated four common ant species in Mountain Fynbos.
The negative ecological impacts of the Argentine ant are numerous and not restricted
to other ant species (Suarez et al. 1998; Sanders et al. 2001) but extend to other invertebrates
and plants (Gomez & Oliveras 2003). Argentine ants can predate directly on other insects
such as Coleoptera (Way et al. 1992), Diptera (Wong et al. 1984) and Hymenoptera (Gambino
1990). In South Africa, displacement of native myrmecochorous ants and pollinators by
Argentine ants potentially threatens more than 170 fynbos plant species (Bond & Slingsby
1984; Visser et al. 1996). In a similar manner, 94 species of myrmecophilous lycaenid
butterfly larvae are seriously threatened by displacement of native ant species tending the
larvae of these butterflies (Migdoll 1994).
Studies of impacts of Argentine ants on non-ant invertebrates are far fewer than those
on ants. Human & Gordon (1997) using pitfall traps in Northern California, found significant
reductions or even the absence of certain taxa in areas invaded by Argentine ants. However,
some invertebrates (mostly alien), are not adversely affected by the presence of Argentine
ants (Cole et al. 1992; Henin & Paiva 2004).
Previous studies on the impact of Argentine ants on saproxylic communities have
focused on single species interactions (Huxel 2000; Henin & Païva 2004). Here I evaluate for
the first time the impact of a) Argentine ants b) pine forestation on a saproxylic
macroinvertebrate community comprizing a large number of point endemic relictual taxa.
METHODS
Study site
The study was carried out in Newlands Forest on the lower south-eastern slopes of Table
Mountain in the Cape Peninsula National Park (Fig. 1) from October to November 2006, at
altitudes of 200-400m. The forest consisted of a mosaic of largely undisturbed native
Afromontane forest and pine plantation, with small stands of eucalyptus and remnant shrubby
Fynbos vegetation. Exotic plantations on the Cape Peninsula were established during the
foundation of the Dutch settlement at the Cape (Spilhaus 1950). The Newlands pine
plantation created in 1670 initially covered 34 ha, and later expanded by a further 17 ha.
Clearing of these pine plantations began in 2001 (Newlands Forestry Manager, pers. comm.).
Study sites were selected to enable comparisons between invaded pine forest and invaded and
uninvaded Afromontane forest (eucalyptus plantation, present in very small and isolated
patches, was not sampled).
Figure 1. Study area showing the Cape Peninsula (A,B) and Newlands Forest (C). Study site indicated by
shaded areas (light grey- Afromontane forest, mid-grey - pine plantation, black- Fynbos vegetation. Dotted area
uninvaded by Argentine ants).
Survey of Argentine ants
To identify areas uninvaded by Argentine ants for deadwood sampling, I first conducted
visual surveys (Underwood and Fisher 2006; Holway 1995) in Afromontane forest by
walking along pathways. The results of this pilot assessment were subsequently confirmed by
placing baited traps comprising 50 ml concentrated sugar water (1.5 kg sugar made up to 2 l
water solution) in plastic jars (70 mm diameter x 75 mm depth). These were sunk flush with
the soil surface, monitored every 2 days and left for one week. Large numbers of drowned
ants up to several hundred/trap were retrieved from these traps in invaded areas..
A separate survey was done on 9th October 2006 to determine the extent of the invasion front.
A transect was carried out during hot weather along a path through the Newlands Forest to the
top of Table mountain, and across the plateau up to Devils Peak (Fig. 1C). Foraging ants
were surveyed visually on and at 20m from the path, at 50m intervals.
Sampling the saproxylic community
Of the 40 stations sampled, 20 were sited in pine plantation, nine in Afromontane forest
invaded by Argentine ants and 11 in Afromontane forest uninvaded by Argentine ants.
Deadwood in pine plantations was abundant, comprising P. radiata alone, whereas deadwood
in Afromontane forest comprised various unidentified species, excluding pine. One moist
deadwood unit between 100-150 cm in length and 15-20 cm diameter, and in an advanced
state of decomposition (easily broken by hand) was selected for sampling at each of the 40
stations. Logs were first carefully moved to collect any macroinvertebrates that lived
underneath, and then placed on a large white plastic sheet where they were opened manually
(using a chisel and hammer where necessary). Each log was then dissected on the spot into
very fine fragments and every visible macroinvertebrate collected with a pooter or forceps and
stored immediately in 70% alcohol (specimens less than 1mm in length were excluded). This
process took approximately 2 hours/log. Specimens were subsequently sorted to
morphospecies which were then identified by experts or for a few groups, using the literature.
Species were then identified as Peninsula endemics, alien species or wider ranging species.
Beetle larvae and juveniles of other taxa (e.g. harvestmen and earthworms) could not readily
be associated with adults, and the latter alone were utilized for data analysis.
Data analysis
Species accumulation curves were generated using the software EstimateS with samples
randomized 50 times (Colwell 2005). Incidence-based Coverage Estimator (ICE) was chosen
to calculate estimated total species richness as it uses the incidence of rare species in samples.
The relationship between the different log communities were analyzed using the
multivariate software PRIMER (Plymouth Routines In Multivariate Ecological Research),
where 4th root transformed abundances were used to produce a Bray Curtis similarity matrix.
The 4th root transformation is suited to samples with abundant and rare species, leading to the
down weighting of abundant species and representation of midrange and rarer species in the
calculations of similarity (Clarke & Warwick 2001). One-way ANOSIM permutation test
(Clarke & Green 1988) was carried out to test for differences between the composition log
communities of pine plantation and Afromontane forest.
RESULTS
Argentine ants were common and widespread in pine forest, occurring in sugar traps at 16 of
the 20 sites. For the section of Afromontane forest invaded by Argentine ants (as censussed
visually), all sugar traps (n=9) collected this species. However, for the section of uninvaded
Afromontane forest, no ants were detected during visual surveys of this area, and none
occurred in the sugar traps, even though these did trap other species of ant (Crematogaster sp,
Tetramorium sp and Monomorium sp). Currently, the uninvaded area in the Afromontane
forest is situated at the northern part of Newlands Forest at higher altitude (above 350 m).
Moreover, the visual survey did not detect any Argentine ants along Newlands ravine and on
the plateau in Fynbos vegetation leading to Devil’s Peak (Fig. 1C), adjacent areas at higher
altitudes. On warm days, Argentine ants were observed foraging on and inside logs (in the
subcortical region) at 3 stations in invaded Afromontane forest and 2 stations in the pine
plantation. An entire colony of Argentine ants with 3 queens was discovered in a rotten log in
pine plantation together with four velvet worms of two species.
In total, the sampled log community comprised 155 morphospecies across five phyla:
Platyhelminthes, Annelida, Mollusca, Onychophora and Arthropoda (Appendix 1).
Fifteen of the 23 higher level taxa occurred in relatively low abundances (Fig. 2).
Numerically, centipedes (Chilopoda), beetles (Coleoptera), spiders (Araneae), millipedes
(Diplopoda), snails and slugs (Mollusca) and harvestmen (Opiliones) dominated in that order.
However, beetles (39 species) followed by spiders (24 species) were the most diverse taxa.
Most of the higher level taxa were recorded more frequently in Afromontane as compared to
pine forest, apart from millipedes, springtails, ants, mites, diplurans, scorpions and booklice.
Chilopoda (10)
Coleoptera (39)
Araneae (24)
Diplopoda (4)
Gastropoda (11)
Opiliones (10)
Formicidae (8)
Isopoda (5)
Collembola (4)
Dermaptera (4)
Annelida (6)
Amphipoda (2)
Acari (9)
Diplura (1)
Onycophora (2)
Hemiptera (9)
Orthoptera (2)
Homoptera (1)
Blattodea (2)
Scorpiones (1)
Archaeognatha (1)
Platyhelmintha (1)
Psocoptera (2)
0
10
20
30
40
50
60
70
80
Figure 2. Total number of occurrences for all species within a higher taxon in the 40 replicate logs in pine
plantation (white), uninvaded Afromontane forest (grey) and invaded Afromontane forest (black). The number of
species recorded for each higher taxon are given in brackets. Counts of species presence have been used instead
of numerical abundance to avoid bias resulting from counts of individual ant colony members.
Species richness
Afromontane forest (invaded and uninvaded patches) with 134 observed species had 1.54
more species than pine forest (88 species). The estimated species richness for Afromontane
forest (n= 348.9) was 2.2 times higher than the value for pine forest (156.4)(Fig. 3). The
accumulation curves do not show asymptotic trends at 20 samples.
400
350
number of species
300
250
200
150
100
50
0
0
5
10
15
20
number of samples
Figure 3. Observed and estimated (squares) species accumulation curves for all species in pine plantation
(dashed line) and in Afromontane forest for both invaded and uninvaded areas (solid line). Accumulation curves
were smoothed by randomizing sample order 50 times.
Logs from Afromontane forest invaded by Argentine ants had a greater species richness (1.18
times) (96 species observed, and 331.3 species estimated) than uninvaded Afromontane forest
(81 species observed at 9 samples, 306.3 species estimated) (Fig. 4).
350
number of species
300
250
200
150
100
50
0
1
2
3
4
5
6
7
8
9
10
11
number of samples
Figure 4. Observed and estimated (marked with square) species accumulation curves for all species in
uninvaded Afromontane forest (dashed line) and in invaded Afromontane forest (solid line). Accumulation
curves were smoothed by randomizing sample order 50 times.
Species assemblage
The MDS plot shows fairly distinctive invertebrate assemblages of pine versus Afromontane
forest logs (Fig. 5). Assemblages of invaded and uninvaded Afromontane forest logs differed
at the 20% level, with assemblages of invaded Afromontane forest falling closer to plots of
pine assemblages, and with some stations falling within the cluster of pine stations.
2D Stress: 0.2
Figure 5. Multidimensional scaling (MDS) plot of invertebrate communities in pine and Afromontane forest
logs. White - Afromontane forest; black - pine plantation; squares - stations in areas invaded by Argentine ants;
diamonds - stations in uninvaded areas. Solid line 30% similarity.
Stations in uninvaded Afromontane forest formed the most distinct cluster, separating from all
other stations (Fig. 6).
0
% similarities
20
40
60
80
100
Samples
Figure 6. Cluster analysis of samples based on their species composition. White - Afromontane forest; black pine plantation. Squares - stations in areas invaded by Argentine ants; diamonds - stations in uninvaded areas.
However, invaded and uninvaded Afromontane forest log communities differed significantly
in species compostion (ANOSIM R= 0.73, 0.1% level). Afromontane forest and pine
plantation also differed significantly in species composition (ANOSIM R= 0.46, 0.1% level).
Cape Peninsula endemics
A number of Cape Peninsula endemics of Gondwanan orgin (Picker & Samways 1996) were
recorded from some of the stations. Two species of centipede (Chilopoda), Cryptops
stupendus and Paralamyctes prendinii were recorded only in uninvaded Afromontane forest.
C. stupendus was previously regarded as a troglobitic species (Sharrat et al. 2000).
Paralamyctes asperulus was found only in invaded areas (Afromontane and pine). The
scorpion Uroplectes insignis was common in pine plantation. The millipede Julomorpha
hilaris occurred commonly at all study sites. Finally, three species of harvestmen
(Cryptadaeum capense, Larifuga capensis and Rostromontia capensis) and the isopod
Trichoniscus capensis were found mostly in Afromontane forest.
Alien species:
A number of alien species were recorded from both pine and Afromontane forest. Four
species of alien earthworms (Aporrectodea caliginosa, Bimastos eiseni, Lumbricus rubellus
and Dendrobaena cognetti) were present both in pine plantation and Afromontane forest. One
species of alien snail (Arion,, Arionidae) and four slug species (Limax maximus, Lehmania sp,
Deroceras reticulatum and Deroceras sp) were recorded mostly in uninvaded Afromontane
forest. Additionally, two alien snail species (Oxychilus draparnaudi and Zonitoides arboreus
Zonitidae) occurred in uninvaded Afromontane forest. The cosmopolitan Porcellio scaber
(Porcellionidae) occurred at all sites except in uninvaded Afromontane forest. The alien
woodlice Porcellionides pruinosus and Armadillidium vulgare did not occur in pine plantation
but only in Afromontane forest. The earwig Euborellia annulipes is a cosmopolitan European
species and was present in both Afromontane forest and pine plantation.
DISCUSSION
Species richness, endemism and invasive species in pine and indigenous forest
Saproxylic communities of pine-transformed indigenous forest were noted to have lower
species richness than those of both invaded and uninvaded Afromontane forest, although
evidently the saproxylic community is impacted far less by forest transformation than other
invertebrate guilds such as herbivores, pollinators and parasitoids, whose diversity would be
expected to drop dramatically in pine-transformed forest with the loss of native hosts
(Holloway et al. 1992). However, the nutritive quality, susceptibility to fungal invasion,
moisture retention, and physical properties of the rotting wood are likely to influence the
nature of the saproxylic communities structure. Thus although Velvet worms were found in
all forest types, Peripatopsis capensis was most abundant in pine forest, and the smaller P.
balfouri was only present in Afromontane forest. On the other hand, species richness of
beetles (25 species) and ants (seven species) in pine logs was comparable to that in
Afromontane forest (29 species of beetles and seven species of ants). Pine plantation was
clearly avoided by snails and slugs which showed a preference for Afromontane forest where
11 species were found whereas only four species were found in pine plantation. Microclimate
and soil properties (pH) are known to govern the distribution patterns of snails (Kappes 2006),
and the acidification of soils in pine plantations (Priha & Smolander 1997; Yeates et al. 2004)
is a likely reason for the exclusion of many snail species from this habitat. On the other hand,
predators such as spiders and centipedes feed on saproxylic species and they therefore have
less exacting habitat requirements.
The majority of surveys of saproxylic fauna have concentrated on a single taxon (typically
beetles) and have used appropriate sampling techniques such as emergence traps.
Xylophagous beetles are suitable indicators because of their close trophic association with
dead and decaying wood. However, the community sampled here represented one in the final
stages of log decay (Grove 2002; Vanderwel 2006). Vanderwel et al. (2006), working in
Canadian pine-dominated forest found that for xylophagous beetle communities, saprophages,
fungivores and parasitoids tended to be most abundant in logs of advanced decomposition,
whereas this study revealed that xylophages (beetles) saprophages (millipedes) and predators
(chilopods and spiders) were the most common taxa in rotting logs.
Manual sorting (or direct sampling) of entire saproxylic communities has rarely been
attempted (Martikainen & Kouki 2003), possibly due to the lengthy period required for
breaking down entire logs and extracting all invertebrates. However, this method has the
advantage of sampling rare species (or threatened species) within an entire saproxylic
community and has the potential to track community responses to biotic and abiotic
environmental change (Martikainen & Kouki 2003). This study revealed community
differences in species composition and abundance between pine and Afromontane forest
rotten log communities. However, the MDS clustering indicates a transitional community in
invaded Afromontane forest sites which links uninvaded Afromontane forest and pine
plantation communities. These sites were situated in Afromontane forest bordering pine
plantation, while the uninvaded Afromontane forest sites were not close to any pine
plantation.
Fifteen out of 155 species were positively identified as introduced species, comprising
seven species of snails and slugs, four species of earthworms, three species of isopods, one
species of earwig and the Argentine ant. All the slugs collected in this study were alien
species probably originating from Europe (Cowie 1998). Their presence is probably a result
of habitat disturbance, although the slug Limax maximus was recorded in uninvaded
Afromontane forest. However, it is noteworthy that the number of introduced snails and slugs
(seven species) in Newlands Forest is 11.6 times lower than the 81 species that have been
introduced on the Hawaiian islands (Cowie 1998). However, alien predaceous snails and slugs
have the greatest potential for negative impacts on endemic invertebrates with restricted
distributions (Cowie 1998). It is therefore of concern that the predaceous snail Oxychilus
draparnaudi was recorded from uninvaded Afromontane forest
The cosmopolitan isopod Porcellio scaber was not present in Argentine ant-free areas but was
common in invaded Afromontane forest and to a lesser extent in pine plantation. Barnard
(1932) mentioned this species as one of six introduced isopods in the Cape Town area. The
presence of this species in undisturbed Afromontane forest is surprising as alien sowbugs are
known to track disturbance (Human & Gordon 1997); the contiguous placement of the
invaded Afromontane forest to pine plantations may explain the presence of this species in
native forest. Alien earthworms occurred largely in Afromontane forest, possibly reflecting an
avoidance for the acidic soils of pine forests (Yeates et al. 2004).
The Cape Peninsula supports a rich concentration of endemic invertebrates (111 species in an
area of 470 km2) (Picker & Samways 1996). Of these, 8 % (nine species) are associated with
litter and rotten logs in moist Afromontane forest. Cryptops stupendus which was previously
recorded only in deep zones of caves (Sharrat et al. 2000) was also found in rotten logs in
uninvaded Afromontane forest. This suggests that other endemic species previously thought
to be restricted to caves might extend their niche to rotting logs. In contrast, the closely
related species Paralamyctes asperulus occurred in invaded but not in uninvaded
Afromontane forest. Some Peninsula endemics have apparently adapted to alien plantation;
the scorpion Uroplectes insignis was very common in pine plantation, and the millipede
Julomorpha hilaris was abundant in all forest types. The latter species and other millipedes
are likely to be resistant to Argentine ants as they are protected by a hard cuticule and
repellent secretion (Lawrence 1984).
Distribution of Argentine ants in Newlands Forest
The survey was conducted during a period coinciding with maximum soil moisture and high
temperatures, ideal conditions for scoring Argentine ant activity (Godlisten 2003). Argentine
ants were found to be widespread within pine plantation as well as in parts of the
Afromontane forest. Only a small portion of Afromontane forest was found to be free of
Argentine ants, although this study area was of the same altitude as the invaded region.
Argentine ants disappeared at altitudes above 600 m, as the forest canopy thinned out and was
replaced by more open, drier Fynbos vegetation approaching, and on the Peninsula plateau
itself. This coincided with increased abundance of native ant species (Polyrhachis sp,
Lepisiota incisa and Crematogaster sp), an indication of the absence of the Argentine ant
(Holway 1995; Sanders et al. 2001). These areas showed no signs of disturbance (apart from
the hiking trails). Environmental factors may thus limit the spread of Argentine ant fronts on
the Cape Peninsula, and microclimate is a well-known determinant of the distribution of some
ant species (Torres 1984). However, at Newlands forest soil moisture is not thought to be the
single limiting factor as both uninvaded and invaded Afromontane forest were very similar in
terms of soil and log moisture. There would appear to be some biotic resistance to the spread
of the Argentine ant in the Western Cape, through interference competition with a native
species, Lepisiota incisa. The two species appear to displace one another on a fine scale, and
each is capable of repelling the other species if it was the first to recruit to baits (Godlisten
2003). A complicating factor in mapping Argentine ant fronts is their propensity to change
according to season and even to retreat from previously occupied areas (Heller et al. 2006).
The impact of Argentine ants on the relict saproxylic fauna
To understand the impact of Argentine ants on saproxylics invertebrates, it is essential to
discriminate different taxa according to their biology and location within deadwood. True
saproxylics (xylophagous and xylomycophagous species) living deep inside logs are relatively
hard to access. It is unlikely that Argentine ants could infiltrate the galleries occupied by
larval or adult beetles. Similarly, Henin and Paiva (2004) found that Argentine ant did not
impact negatively on the boring scolytid beetle Orthotomicus erosus. Likewise, Velvet
worms, known for their ability to occupy small and isolated cavities in logs, and are unlikely
to be vulnerable to ant predation. Gagne (1979) found that only borers, vagile species and gall
formers are resistant to the presence Argentine ants. Native ant species had greater richness
and abundance in logs of invaded Afromontane forest (seven species) compared to uninvaded
areas (two species), a result that contrasts with previous findings where Argentine ants
typically displaced native ants in the Western Cape Province of South Africa (Donnelly &
Giliome 1985; Suarez et al. 1998). The former dominates in terms of abundance (Aron 2001)
and ability to recruit over short time periods (Godlisten 2003). Visual surveys and bait-trap
results of this study confirmed findings from other studies (e.g. Holway 1995) that no native
ant species forage in the presence of recruiting and foraging Argentine ants at baits (Holway
1995). Moreover, hypogaeic ants are less likely to be displaced than above ground foragers
(Donnelly and Giliome 1985; Ward 1987; Human & Gordon 1997;). The dominant groups
living superficially on deadwood (under bark or in surface cavities), and thus potentially more
vulnerable to Argentine ant attack are spiders, snails and harvestmen. However, spiders were
not much affected by Argentine ants (13 species found in invaded Afromontane versus 15
species found in uninvaded Afromontane forest). Similarly, Holway (1998) found that
Argentine ants do not have a noticeable negative impact on spiders in Northern California
woodland. Vulnerable taxa are likely to have little defence or retreat mechanisms; such as the
small native Afromontane snails (Trachycyctis sp and Nata) as the latter were absent in
invaded Afromontane forest (see Appendix 1).
Implications for conservation of the saproxylic fauna of Afromontane forests
The Cape Peninsula presents an unusual conservation paradox, in that it supports an
exceptionally high number of local endemic invertebrates (8% of which are saproxylic), many
of which are faced with the combined threat of pine forestation and impact of Argentine ants..
Moreover, a high proportion of this saproxylic community have a unique phylogenetic
position, comprising basal lineages of Gondwanan origin (Picker & Samways 1996).
Examples include the harvestman Purcellia, velvet worms Peripatopsis, king crickets
Henicus, centipedes Lamyctes, Paralamycte and Cryptops, endodontid snails Trachycystis, the
daddy longleg spider Spermophora, the sicariid spider Drymusa, bristletails Meinertellidae,
and amphipod Talitriator.
My results show that pine plantations have a reduced species richness of saproxylic
invertebrates, with an approximate loss of 50% of the native species. This finding is
consistent with that of Ratsirarson et al. (2002) who studied the litter fauna in the same
forests. Nevertheless, pine logs did support Cape Peninsula endemic species such as the local
endemic scorpion Uroplectes insignis, restricted to Newlands Forest itself (Leeming 2003) as
well as taxa of Gondwanan origin (the velvet worm Peripatopsis capensis). As part of the
management policy of the South African National Parks who manage the Cape Peninsula
Reserve, clearing of pine plantations was initiated in 2001 and is still currently being
undertaken, with the replacement of felled pines with indigenous trees (40 000 saplings have
been planted to date). Since pine deadwood was found to offer suitable habitat for a number
of endemic saproxylics, a proportion should be left in situ following felling operations. The
impact of an open canopy on Argentine ant populations needs further investigation.
(disturbance and fragmentation caused by canopy removal is known to attract Argentine ants
elsewhere - Human et al. 1998).
This study has shown little negative impact by Argentine ants of saproxylic
communities of the Cape Peninsula forests, in fact a somewhat greater species richness was
found in invaded areas of Afromontane forest. While other factors would undoubtably have
contributed to species richness, a clearcut negative impact by Argentine ants was not
demonstrated. While the presence of alien invertebrates in pine forest was to be expected, the
penetration of such species into pristine Afromontane forest was a surprising result, especially
since some were restricted to this habitat. Such species (especially carnivorous taxa) might
well threaten some of the narrow endemics that share the saproxylic niche.
.
Acknowledgements
I am grateful to the following experts for assistance in the identification of specimens: Danuta
Plisko (Natal Museum, South Africa), Charles Griffiths (University of Cape Town, South
Africa), Greg Edgecombe (Australian Museum), Norman Larsen (Honorary curator of
arachnids , Iziko Museums, Cape Town), Dai Herbert (Natal Museum, South Africa), Adriano
Kury and Amanda Mendes (National Museum of Rio de Janeiro).
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Appendix 1. List of species collected from rotten logs. Numbers are abundance of each species, with number of
stations in which they occurred bracketed.
Taxa
Status of endemicity
P: Platyhelmintha Unindentified
P: Molluscs C: Gastropoda
F: Arionidae
Arion sp
F: Limacidae
Deroceras sp
Deroceras reticulatum
Lehmannia sp
Unknown
Afromontane
uninvaded
3
(2)
Afromontane
invaded
2
(2)
Pine
invaded
0
(0)
Alien
4
(3)
6
(3)
2
(2)
Alien
Alien
Alien
2
3
2
(2)
(2)
(2)
1
18
0
(1)
(1)
(0)
0
1
0
(0)
(1)
(0)
Limax maximus
F: Charopidae
Trachycystis charibdis
Trachycystis tollini
Trachycystis prionacis
F: Rhytidae: Nata tarachodes
F: Zonitidae
Oxychilus sp
Zonitoides arboreus
P: Annelida
F: Acanthodrilidae
Dichogaster sp
Parachilota sp
F: Lumbricidae
Aporrectodea caliginosa
Bimastos eiseni
Dendrobaena cognetti
Lumbricus rubellus
C: Chilopoda
O: Scolopendromorpha
F: Cryptopidae
Cryptops australis
Cryptops stupendus
F: Scolopendridae
Cormocephalus anceps anceps
O: Geophilomorpha
F: Aphilodontidae
Aphilodon weberi
F: Geophilidae sp1
O: Lithobiomorpha
F: Henicopidae
Lamyctes africanus
Paralamyctes prendinii
Paralamyctes asperulus
Paralamyctes weberii
Anopsobius patagonicus calcaratus
C: Diplopoda
O: Spirostreptida
F: Julomorphidae
Julomorpha hilaris
F: Harpagophoridae
Harpagophora sp
O: Polydesmida
F: Sphaerotrichopidae
Sp1
Sp2
O: Oniscomorpha
F: Sphaerotheriidae: Sphaerotherium sp
C: Arachnida Scorpiones
Uroplectes insignis
C: Arachnida Araneae
sO: Mygalomorpha F: Migidae
Moggridgea teresa
sO: Araneomorpha
F: Drymusidae: Drymusa capensis
F: Gnaphosidae
Zelotes sp
Sp1
Sp 2
F: Hahniidae: Sp1
F: Liniphiidae Sp1
F: Palpimanidae: Ikuma sp
F: Philodromidae: Tibellus sp
F: Pholcidae
Spermophora sp
Sp1 (Pholcinae)
F: Phyxelidae: Malaika longipes
F: Salticidae
Sp1
Sp2
F: Scytodidae
Alien
2
(2)
0
(0)
0
(0)
1
11
1
5
(1)
(6)
(1)
(4)
0
1
0
0
(0)
(1)
(0)
(0)
0
0
0
0
(0)
(0)
(0)
(0)
0
3
(0)
(3)
26
0
(6)
(0)
3
1
1
(1)
Afromontane
Afromontane
0
10
(0)
(6)
1
3
(1)
(2)
0
0
(0)
(0)
Alien
Alien
Alien
Alien
2
34
0
13
(2)
(6)
(0)
(5)
0
14
2
1
(0)
(3)
(1)
(1)
0
9
0
0
(0)
(3)
(0)
(0)
Probably endemic
Cape Peninsula endemic
10
35
(7)
(6)
1
0
(1)
(0)
5
0
(5)
0
Widespread
17
(7)
32
(6)
24
(10)
Widespread
Unknown
20
4
(9)
(4)
14
3
(4)
(2)
9
7
(4)
(6)
Widespread
Cape Peninsula endemic
Cape Peninsula endemic
Widespread
Cape Peninsula endemic
8
3
0
3
2
(5)
(3)
(0)
(3)
(2)
23
0
5
9
0
(6)
(0)
(2)
(3)
(0)
41
0
5
3
0
(14)
(0)
(4)
(3)
(0)
Cape Peninsula endemic
20
(6)
111
(8)
39
(6)
Unknown
26
(8)
29
(8)
132
(20)
Unknown
Unknown
0
2
(0)
(1)
0
13
(0)
(2)
9
13
(5)
(6)
Unknown
0
(0)
13
(2)
0
(0)
Newlands endemic
0
(0)
1
(1)
6
(5)
Widespread
1
(1)
0
(0)
0
(0)
Widespread
0
(0)
4
(3)
0
(0)
Widespread
Un known
Unknown
Unknown
Unknown
Unknown
Unknown
0
1
3
1
0
1
1
(0)
(1)
(1)
(1)
(0)
(1)
(1)
1
1
0
0
3
0
0
(1)
(1)
(0)
(0)
(2)
(0)
(0)
1
0
0
0
0
0
0
(1)
(0)
(0)
(0)
(0)
(0)
(0)
0
3
49
(0)
(2)
(9)
3
6
11
(1)
(3)
(5)
0
3
0
(0)
3
(0)
0
1
(0)
(1)
0
0
(0)
(0)
1
0
(1)
(0)
Afromontane
Afromontane
Afromontane
Afromontane
Alien
Alien
Unknown
Unknown
Cape Peninsula endemic
Unknown
Unknown
Scytodes sp1
Scytodes sp2
F: Tetragnathidae: sF: Metinae sp1
F: Theridiidae
Steotoda capensis
Theridion sp
Sp1
Sp2
F: Uloboridae: Uloboris sp
F: Zordariidae: Cydrelinae sp
F: Zoropsidae: Panotea ceratogyrus
C: Arachnida Opiliones Cyphophthalmi
F: Petallidae: Purcellia illustrans
C: Arachnida Opiliones Laniatores
F: Triaenonychidae
Gunvoria spatulata
Rostromontia sp
Larifuga capensis
Cryptadaeum capense
Paramontia lisposoma
Planimontia goodnightorum
Rostromontia capensis
C: Arachnida Opiliones Palpatores
Neopilioninae sp1
C: Acari
Sp1
Sp2
Sp3
Sp4
Sp5
Sp6
Sp7
Sp8
Sp9
P: Onycophora: Peripatopsidae
Peripatopsis capensis
Peripatopsis balfouri
C: Crustacea: Isopoda
F: Porcellionidae
Porcellio scaber
Porcellionides pruinosus
Armadilidium vulgare
F: Trichoniscidae
Trichoniscus capensis
Sp1
C: Amphipoda F: Talitridae
Talitriator setosa
Talitriator cylindripes
Collembola
F: Entomobryidae
Sp1
Sp2
F: Hypogastruridae sp1
F: Onychiuridae sp1
Diplura
F: Campodeidae Sp1
O: Archaeognatha
F: Meinertellidae
Machiloides dubius
O: Dermaptera
F: Forficulidae
Alloblandex granulatus
Forficula sp
F: Labiduridae
Euborellia annulipes
F: Labiduridae
Brachylabis
O: Orthoptera
F: Anostostomatidae
Henicus brevimucronatus
F: Gryllidae
Unknown
Unknown
Unknown
4
1
2
(3)
(1)
(2)
0
0
1
(0)
(0)
(1)
0
0
2
(0)
(0)
(1)
Widespread
Widespread
Unknown
Unknown
Widespread
Unknown
Widespread
0
0
1
0
0
1
1
(0)
(0)
(1)
(0)
(0)
(1)
(1)
6
6
1
1
2
0
0
(6)
(4)
(1)
(1)
(1)
(0)
(0)
9
4
0
0
0
1
0
(5)
(3)
(0)
(0)
(0)
(1)
(0)
Widespread
0
(0)
1
(1)
2
(2)
Afromontane
Unknown
Cape Peninsula endemic
Cape Peninsula endemic
Afromontane
Afromontane
Cape Peninsula endemic
1
4
2
1
6
1
3
(1)
(2)
(1)
(1)
(6)
(1)
(2)
0
1
1
0
0
2
0
(0)
(1)
(1)
(0)
(0)
(1)
(0)
0
0
0
0
0
6
1
(0)
(0)
(0)
(0)
(0)
(4)
(1)
Unknown
8
(7)
5
(3)
0
(0)
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
1
0
0
1
1
0
1
0
2
(1)
(0)
(0)
(1)
(1)
(0)
(1)
(0)
(2)
0
1
0
0
0
0
1
4
2
(0)
(1)
(0)
(0)
(0)
(0)
(1)
(3)
(2)
0
0
1
0
0
2
7
21
0
(0)
(0)
(1)
(0)
(0)
(2)
(4)
(6)
(0)
Afromontane
Afromontane
13
0
(9)
(0)
1
0
(1)
(0)
3
5
(1)
(5)
Alien
Alien
Alien
0
6
17
(0)
(3)
(6)
82
1
0
(8)
(1)
(0)
28
0
0
(5)
(0)
(0)
Cape Peninsula endemic
Unknown
12
3
(4)
(3)
5
3
(1)
(1)
11
3
(4)
(1)
123
4
(11)
(2)
21
1
(5)
(1)
2
13
(1)
(6)
Unknown
Unknown
Unknown
Unknown
3
0
0
0
(2)
(0)
(0)
(0)
35
0
21
9
(7)
(0)
(6)
(3)
0
3
26
8
(0)
(2)
(12)
(5)
Unknown
0
(0)
60
(9)
98
(11)
Widespread
8
(5)
1
(1)
0
(0)
widespread
unknown
1
8
(1)
(3)
0
5
(0)
(3)
0
0
(0)
(0)
Alien
7
(3)
8
(2)
2
(2)
34
(9)
33
(7)
34
(5)
7
(4)
5
(3)
0
(0)
Widespread
Widespread
Afromontane
Southern Africa endemic
Cophogryllus sp
O: Blattodea
F: Blattidae
Pseudoderopeltis sp
F: Blattellidae
Sp1
O: Coleoptera
F: Bostrichidae
Sp1
Sp2
F: Anobiidae
Sp1
F: Ptinidae Sp1
F: Corilophidae Sp1
F: Carabidae
Sp1
Sp2
Sp3
Sp4
Chlaeniinae Sp5
Pachyodontus languidus
F: Curculionidae
Sp1
Sp2
Sp3
Sp4
Sp5
Sp6
Sp7
F: Cucujidae
Sp1
Sp2
Sp3
F: Elateridae
Sp1
F: Pselaphidae
Sp1
F: Staphylinidae
Sp1
Sp2
Sp3
Sp4
Sp5
Sp6
Sp7
Sp8
Sp9
F: Scydmanidae
Sp1
Sp2
Sp3
F: Tenebrionidae
Louprops sp
Sp2
Eutochia pulla
Atocrates simius
O: Hemiptera
F: Enicocephalidae
Sp1
F: Lygaeidae
Rhyparochrominae sp1
Sp1
Ectrichodiinae
Acanthaspis
Sp2
O: Homoptera
F: Cixiidae
Cixius sp
O: Psocoptera
F: Pachytroctidae
Lesneia sp
Southern Africa endemic
0
(0)
1
(1)
3
(2)
Widespread
2
(2)
3
(3)
1
(1)
Unknown
1
(1)
0
(0)
0
(0)
Unknown
Unknown
0
0
(0)
(0)
1
3
(1)
(1)
1
0
(1)
(0)
Unknown
Unknown
Unknown
0
0
0
(0)
(0)
(0)
1
1
0
(1)
(1)
(0)
0
1
1
(0)
(1)
(1)
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
0
0
3
2
2
1
(0)
(0)
(3)
(1)
(1)
(1)
3
1
1
2
0
0
(2)
(1)
(1)
(2)
(0)
(0)
1
0
0
0
1
1
(1)
(0)
(0)
(0)
(1)
(1)
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
1
0
1
0
0
0
1
(1)
(0)
(1)
(0)
(0)
(0)
(1)
0
1
0
0
4
0
0
(0)
(1)
(0)
(0)
(3)
(0)
(0)
0
0
0
1
1
3
0
(0)
(0)
(0)
(1)
(1)
(2)
(0)
Unknown
Unknown
Unknown
0
0
0
(0)
(0)
(0)
2
2
42
(2)
(1)
(4)
7
4
15
(4)
(2)
(7)
Unknown
1
(1)
0
(0)
0
(0)
Unknown
0
(0)
0
(0)
2
(1)
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
Unknown
0
1
0
0
0
0
2
18
0
(0)
(1)
(0)
(0)
(0)
(0)
(1)
(7)
(0)
0
0
1
1
0
1
0
28
0
(0)
(0)
(1)
(1)
(0)
(1)
(0)
(7)
(0)
2
1
0
0
3
4
0
39
1
(2)
(1)
(0)
(0)
(2)
(1)
(0)
(8)
(1)
Unknown
Unknown
Unknown
0
0
0
(0)
(0)
(0)
0
0
0
(0)
(0)
(0)
2
1
1
(1)
(1)
(1)
Unknown
Widespread
Widespread
1
0
0
0
(1)
(0)
(0)
(0)
3
1
2
1
(1)
(1)
(2)
(1)
3
0
8
3
(2)
(0)
(5)
(3)
Unknown
2
(2)
0
(0)
0
(0)
Unknown
Unknown
Unknown
Unknown
Unknown
0
1
0
0
0
(0)
(1)
(0)
(0)
(0)
2
6
0
0
1
(1)
(3)
(0)
(0)
(1)
1
2
1
1
1
(1)
(1)
(1)
(1)
(1)
Widespread
4
(4)
5
(4)
1
(1)
Widespread
0
(0)
0
(0)
2
(2)
F: Trogiidae
Helenatropos
O: Hymenoptera
F: Formicidae
Tetramorium grassii
Tetramorium sp2
Monomorium tablense
Camponotus sp
Linepithema humile
Hypoponera sp1
Hypoponera sp2
Widespread
0
(0)
0
(0)
1
(1)
Afromontane
Unknown
Afromontane
Unknown
Alien
Widespread
Widespread
0
(0)
(5)
(0)
(0)
(0)
(0)
(0)
colon
(2)
(1)
(3)
(0)
(3)
(3)
(2)
Col
(1)
(1)
(7)
(4)
(3)
(1)
(1)
0
0
0
0
0
0
7
17
7
10
10