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Community structure of epigaeic ants in a pine plantation and in newly burnt fynbos
... Ant diversity declines in fynbos invaded by hakeas or pines (Donnelly and Giliomee 1985b;Koen and Breytenbach 1988); elaiosome-gathering ants are virtually eliminated in the latter habitat (Donnelly and Giliomee 1985b). Ant species composition is also very different in forest stands, and there are no seed-gatherers among the ground-foraging species (Koen and Breytenbach 1988). ...
... Ant diversity declines in fynbos invaded by hakeas or pines (Donnelly and Giliomee 1985b;Koen and Breytenbach 1988); elaiosome-gathering ants are virtually eliminated in the latter habitat (Donnelly and Giliomee 1985b). Ant species composition is also very different in forest stands, and there are no seed-gatherers among the ground-foraging species (Koen and Breytenbach 1988). ...
Human activities are causing species extinctions at a rate and magnitude rivaling those of past geologic extinction events.
Exploring mediterranean-type ecosystems - the Mediterranean Basin, California, Chile, Australia, and South Africa - this volume addresses the question whether biological diversity plays a significant role in the functioning of natural ecosystems, and to what extent that diversity can be reduced without causing system malfunction. Comparative studies in ecosystems that are similar in certain respects, but differ in others, offer considerable scope for gaining new insights into the links between biodiversity and ecosystem functioning.
... This is consistent with several studies, where ant species richness was generally higher in areas that were burned at least once in the past (e.g. Andersen, 1991;Donnelly & Giliomee, 1985). Although the responses of ant assemblages to fire are complex, research investigating these responses in the immediate aftermath of a fire episode found no change to decreases in ant species richness , and such responses were associated with the physical damages of fire. ...
Early naturalists such as Humboldt observed that changes in topography and anthropogenic disturbances influenced vegetation structure and the composition of animal communities. This holistic view of community assembly continues to shape conservation and restoration strategies in an era of landscape degradation and biodiversity loss. Today, remote sensing affords ecologists the tools for obtaining rapid and precise measures of topography, disturbance history and vegetation structure. Nonetheless, the capacity of such measures to predict the structure of diverse and functionally important insect communities has not been fully explored.
We sampled ground‐dwelling ant assemblages with pitfall traps along a successional gradient (15 grasslands, 21 shrublands and 44 forests) in subtropical Asia, and measured the taxonomic (TD) and functional diversity (FD). We used airborne Light Detection and Ranging (LiDAR) and aerial photography—to measure topography, anthropogenic‐fire history and vegetation structure at each site. Using structural equation models, we tested the hypothesis that vegetation structure mediated the effects of topography and anthropogenic‐fire history on ant assemblage TD and FD, with stronger effects on the latter.
We found that low elevation and anthropogenic‐fire history promoted ant TD, and by mediating vegetation structure, these factors further controlled ant FD. Specifically, assemblages of ant species occupying more similar niches—as indicated by their lower FD—were found in secondary forests that had more structurally homogeneous vegetation. These sites also had low insolation and high water moisture content, and were not recently burned as revealed by LiDAR‐derived metrics and aerial images. Furthermore, remotely sensed vegetation structures were closely associated with individual ant traits, such as body size and eye length, which reflect species' preferences for habitat structure.
Synthesis . Our study uncovers the interactive effects of topography, disturbance history and vegetation structure in determining the TD and FD of ant assemblages in subtropical landscapes. Moreover, it demonstrates that remote sensed data can be leveraged to efficiently elucidate the complex effects of environmental change and disturbances on vegetation structure and consequently insect biodiversity, representing ecological proxies to refine ground investigation plans and support appropriate conservation and restoration measures for degraded landscapes.
... Dins l´ambit d´aquest treball, s´han estudiat diversos grups d´invertebrats epiedàfics i hipogeus i entre ells les formigues. Aquest grup d'insectes ha demostrat abastament respondre a canvis en l'estructura o a pertorbacions en els ecosistemes(Folgarait, 1998) i s'ha usat en aquest sentit en diverses zones del món: Austràlia(Andersen, 1990;King et al. 1998), Amèrica del Nord(Rice, 1932), Sudàfrica(Donnelly, D. & Giliomee, J.H., 1985), ...
S’ha analitzat l’efecte del incendi forestal ocorregut a la franja oriental del Parc
Natural de Sant Llorenç del Munt l’Obac l’agost de 2003 i els posteriors tractaments
post-incendi sobre la vegetació i la fauna de la zona. Quatre anys després de
l’incendi s’observa una simplificació en l’estructura de la vegetació amb pèrdua dels
estrats arbori i arbustiu i augment de l’estrat herbaci. No s’han detectat efectes en la
vegetació degudes als tractaments post-incendi, tot i que la zona subsolada
presenta risc d’erosió especialment si es produeixen gran episodis de pluges. Quant
a la fauna, s’han censat 25523 animals de 70 grups taxonòmics diferents. S’han
determinat a nivell d’espècie els gasteròpodes, formigues de terra i de vegetació,
heteròpters de terra, coleòpters de vegetació, ortòpters, rèptils, aus, carnívors i
quiròpters. D’aquests grups s’han identificat 257 espècies, el 18% de les quals
només han estat localitzades en el bosc mentre que un altre 17% només s’han
localitzat en les zones cremades. Aquestes pèrdues i guanys de diversitat afecten a
tots els grups taxonòmics i indiquen que els paisatges heterogenis amb una barreja
d’espais oberts i bosc poden incrementar notablement la biodiversitat global. Els
grups taxonòmics responen de diferent manera als tractaments: l’extracció de fusta
afavoreix la riquesa d’espècies d’alguns grups i perjudica a la d’altres. Per aquesta
raó és aconsellable la creació de mosaics amb diferent gestió post-incendi que
afavoreixin una restauració més completa de les zones cremades. La recurrència
d’incendis juntament amb l’ús de les zones cremades per a la pastura han provocat
una reducció de biodiversitat probablement com a conseqüència de l’efecte
combinat dels dos factors.
... Acacias, in particular form dense stands, maintain a high leaf area all through the year and have high evapotranspiration which impacts water yields of infested catchments (Dye and Jarmain 2004). In South Africa, these species have also had negative impacts on grassland birds (Allan et al. 1997;Armstrong and Van Hensbergen 1995), small mammals (Armstrong and Van Hensbergen 1995), invertebrates (Donnelly 1985) and plants (Richardson and Van Wilgen 1986). ...
Invasive alien species threaten tropical grasslands and native biodiversity across the globe, including in the natural mosaic of native grasslands and forests in the Shola Sky Islands of the Western Ghats. Here, grasslands have been lost to exotic tree invasion (Acacias, Eucalyptus, and Pines) since the 1950s, but differing invasion intensities between these species and intermixing with native species constitutes a major challenge for remotely sensed assessments. In this study, we assess the accuracy of three satellite and airborne remote sensing sensors (Sentinel-1 radar data, Sentinel-2 multispectral data and AVIRIS-NG hyperspectral data) and three machine learning classification algorithms to identify the spatial extent of native habitats and invasive tree species. We used the support vector machine (SVM), classification and regression trees (CART), and random forest (RF) algorithms implemented on the Google Earth Engine platform. Results indicate that AVIRIS-NG data in combination with SVM produced the highest classification accuracy (98.7%). Fused Sentinel-1 and Sentinel-2 produce 91% accuracy, while Sentinel-2 alone yielded 91% accuracy; but only with higher coverage of ground control points. The hyperspectral data (AVIRIS-NG) was the only sensor that permitted distinguishing recent invasions (young trees) with high precision. We suspect that large areas will have to be mapped and assessed in the coming years by conservation managers, NGOs to plan restoration or to assess the success of restoration activities, for which a choice of sensors may have to be made based on the age of invasion being mapped, and the quantum of ground control data available.
... Acacias, in particular form dense stands, maintain a high leaf area all through the year and have high evapotranspiration which impacts water yields of infested catchments (Dye and Jarmain 2004). In South Africa, these species have also had negative impacts on grassland birds (Allan et al. 1997;Armstrong and Van Hensbergen 1995), small mammals (Armstrong and Van Hensbergen 1995), invertebrates (Donnelly 1985) and plants (Richardson and Van Wilgen 1986). ...
Invasive alien species (IAS) threaten tropical grasslands and native biodiversity and impact ecosystem service delivery, ecosystem function, and associated human livelihoods. Tropical grasslands have been dramatically and disproportionately lost to invasion by trees. The invasion continues to move rapidly into the remaining fragmented grasslands impacting various native grassland-dependent species and water streamflow in tropical montane habitats. The Shola Sky Islands of the Western Ghats host a mosaic of native grasslands and forests; of which the grasslands have been lost to exotic tree invasion (Acacias, Eucalyptus and Pines) since the 1950s. The invasion intensities, however, differ between these species wherein Acacia mearnsii and Pinus patula are highly invasive in contrast to Eucalyptus globulus. These disparities necessitate distinguishing these species for effective grassland restoration. Further, these invasive alien trees are highly intermixed with native species, thus requiring high discrimination abilities to native species apart from the non-native species. Here we assess the accuracy of various satellite and airborne remote sensing sensors and machine learning classification algorithms to identify the spatial extent of native habitats and invasive trees. Specifically, we test Sentinel-1 SAR and Sentinel-2 multispectral data and assess high spatial and spectral resolution AVIRIS-NG imagery identifying invasive species across this landscape. Sensor combinations thus include hyperspectral, multispectral and radar data and present tradeoffs in associated costs and ease of procurement. Classification methods tested include Support Vector Machine (SVM), Classification and Regression Trees (CART) and Random Forest (RF) algorithms implemented on the Google Earth Engine platform. Results indicate that AVIRIS-NG data in combination with SVM recover the highest classification skill (Overall - 98%, Kappa-0.98); while CART and RF yielded < 90% accuracy. Fused Sentinel-1 and Sentinel-2 produce 91% accuracy, while Sentinel-2 alone yielded 91% accuracy with RF and SVM classification; but only with higher coverage of ground control points. AVIRIS-NG imagery was able to accurately (97%) demarcate the Acacia invasion front while Sentinel-1 and Sentinel-2 data failed. Our results suggest that Sentinel-2 images could be useful for detecting the native and non-native forests with more ground truth points, but hyperspectral data (AVIRIS-NG) permits distinguishing, native and non-native tree species and recent invasions with high precision using limited ground truth points. We suspect that large areas will have to be mapped and assessed in the coming years by conservation managers, NGOs to plan restoration, or to assess the success of restoration activities, and several data procurement and analysis steps may have to be simplified.
... Here, strong congruence in assemblage variation was restricted to local scales (250-475 m), and only present between the entire plant assemblage and arthropods sampled from the vegetation when ants were removed. Within the fire-prone fynbos, ants show great resilience to fire (Donnelly and Giliomee 1985, Pryke and Samways 2011, which could explain why their exclusion can improve congruence between plant and foliar arthropod assemblage variation at local scales. Non-ant foliar arthropod assemblage variation also showed a significant relationship with that of KSF-endemics at the landscape scale, but this relationship was not very strong, and only present when the analysis was weighted by sampling frequency. ...
Plants often form the basis of conservation planning and management. The effectiveness of plant diversity as a surrogate for arthropod diversity was assessed in natural areas in the Kogelberg Biosphere Reserve, a floral endemism hotspot in the Cape Floristic Region (CFR), South Africa. Arthropods and plants were sampled across 30 topographically heterogeneous sites in a spatially nested design. The relationship between plants and arthropods were quantified in terms of species richness, assemblage variation, and assemblage turnover. The influence of arthropod trophic groups, habitat association, and spatial scale were also explored. Generalized dissimilarity modelling was used to investigate differential influence of explanatory groups (geology, disturbance, local site characteristics, refuge, mesoclimate, terrain) on arthropod and plant turnover. Congruence in assemblage variation was restricted to local scales, and only present between plants and those arthropods associated with the foliar component of the habitat. Weak congruence in species turnover was due to differences in the relative importance of explanatory groups, with different variables within each explanatory group being important, and similar variables predicting different turnover patterns. For both groups, variables related to geology and fire history were important for assemblage turnover. These variables are already incorporated in conservation planning and management for plant diversity across the CFR. Overall plant diversity was a weak surrogate for the arthropod groups included in this study, suggesting that as an alternative, environmental surrogates for arthropod diversity perform better. This article is protected by copyright. All rights reserved.
... En le ámbito de este trabajo, se han estudiado diversos grupos de invertebrados epiedáficos y hipogeos, y entre ellos las hormigas. Este grupo de insectos ha demostrado sobradamente responder a cambios en la estructura y a perturbaciones en los ecosistemas (Folgarait, 1998) y se ha usado en este sentido en diversas zonas del mundo: Australia (Andersen, 1990;King et al., 1998), América del Norte (Rice, 1932), Sudáfrica (Donnelly & Giliomee, 1985), Sudamérica Brown, 1997) y Europa (Garcia et al., 1995;Gomez et al., 2003;Gibb & Hjälten, 2007). El efecto de los incendios en las hormigas se ha estudiado de manera específica, aunque la mayoria de trabajos -como este-son observacionales, a posteriori, de los efectos del fuego en las hormigas y, en este sentido, no pueden se predictivos sinó tan sólo descriptivos o correlacionales. ...
... Here we examine the effects of a large-scale fire on the springtail fauna of a fynbos ecosystem in the Western Cape of South Africa, using a study including information from before the fire and then for a period of three years after it. Earlier studies on the response of invertebrates to fire in this system have focused on insects (Donnelly and Giliomee, 1985;de Kock et al., 1992;Pryke and Samways, 2012). The responses of other arthropod groups remain largely unknown, or at best understood at the scale of response of entire higher taxa such as families (Pryke and Samways, 2012). ...
Background: Increasing numbers of invasive alien plant (IAP) species are establishing around
the globe and can have negative effects on resident animal species function and diversity.
These impacts depend on a variety of factors, including the extent of invasion, the region and
the taxonomic group affected. These context dependencies make extrapolations of IAP impacts
on resident biota from region to region a substantial challenge.
Objectives: Here, we synthesised data from studies that have examined the effects of IAPs on
animal diversity in South Africa. Our focus is on ectothermic organisms (reptiles, amphibians
and invertebrates).
Method: We sourced relevant articles using keywords relating to (1) the effects of IAPs on
species diversity (abundance, richness and composition), (2) the IAP and (3) the native
ectotherm. We extracted the taxonomic and spatial coverage of IAPs and affected native species
and assessed the extent of information given on potential mechanisms driving IAP impacts.
Results: Across the 42 studies, IAPs had a decreasing or neutral effect on native animal
abundance and richness and significantly changed species composition. This review
highlighted the paucity of studies and the research deficits in taxonomic and geographic
coverage and in the mechanisms underlying IAP impacts on ectotherms.
Conclusion: By assessing the status of knowledge regarding the impacts of IAPs on resident
animal species in South Africa, this study identifies information gaps and research priorities at
the country level with a view to informing monitoring and conservation efforts, such as alien
plant removal and control programmes, and ensuring that endemic terrestrial animal diversity
is maintained.
The largest population of Diastella buekii, previously considered extinct, occurs in a Pinus pinaster plantation in La Motte State Forest in the Berg River valley in the western Cape Province. Treatments were applied to 1-ha plots in a compartment of the plantation. Mortality in Diastella ranged from 87.5% to 100% between 1982 and 1987 with no treatment and with treatments of thinning the pines, burning under the pines, or both. Clear-felling the pines on 2ha of the study site, and a burn three and a half years later, promoted regeneration, and resulted in a 29.4% increase in the population between 1982 and 1987. No Argentine ant invasion has been found on this site and seed dispersal by indigenous ants is not disrupted. A strong relationship between the distribution of Diastella and minor changes in relief suggests that depth to the water table plays a key rôle in the plants’ distribution. The influences of adjacent plantations on the water table may adversely affect Diastella populations. It is concluded that D. buekii will become locally extinct unless the pine plantation is removed. No management problems are foreseen if these steps are taken.
Following a demonstration of the role of ants in the dissemination of Phytophthora pod rot and an intensive study of the ant mosaic on cocoa at the Cocoa Research Institute of Nigeria, there was a need for a wide-scale assessment of the relative importance of different species of ant on cocoa farms in the major growing area of western Nigeria. Between 19 January and 6 February 1976, 50 trees were examined on each of 76 cocoa farms and all ant species visible from the ground were recorded. Sixteen species, or species-groups, of ants occurred on more than 1% of the trees, and their geographical distribution, habitat requirements and inter-specific relations were examined. The last of these were elucidated using principal components analysis, and the results are compared with earlier work on the ant mosiac. Any one cocoa farm only rarely provided a suitable habitat for more than one or two of the dominant species, and a diagram summarising the habitats is given. The potential usefulness of ant population manipulation is thought to be restricted in Nigeria by the undesirable effects of co-dominant and associated species found with the dominant species, Oecophylla longinoda (Latr.) and Tetramorium aculeatum (Mayr), which are regarded as beneficial in Ghana. The most important of the undesirable co-dominants is Pheidole megacephala (F.).
The distribution of ants in a 2·25-ha cocoa plantation at the University of Ghana Agricultural Research Station, Kade, was recorded in December 1970. The 44 species of ants found could be grouped as dominant, co-dominant, sub-dominant and nondominant. Oecophylla longinoda (Latr.) and Macromischoides aculeatus (Mayr) were mutually exclusive as were six Crematogaster spp.; the latter were also exclusive of O. longinoda and M. aculeatus. Camponotus acvapimensis Mayr became dominant under insolated conditions, and Platythyrea frontalis Emery for reasons unknown. The distribution of these ant species in cocoa plantations resembles a three-dimensional mosaic which is preserved by their aggressiveness and by competition for food and nesting sites. It is suggested that this mosaic is due to vegetative succession.(Received April 20 1971)(Revised February 09 1972)
The plants and Homoptera on three old fields in southeast Michigan were sampled. Within fields, correlations between plant and insect diversity were generally weak. But using all samples from three fields, evenness (J) and diversity (H) of the insects were highly correlated with plant evenness and plant diversity, respectively. For example, 72% of the variance in insect H could be accounted for by variation in plant H. Number of species (S) showed a positive but weaker correlation. When correlations were based on the pooled samples from each field, all three statistics for insects were highly correlated with those for the plants. Insect H was also highly correlated with plant structure (foilage height diversity FHD) over all three fields. These two measures of plant diversity (H and FHD) were highly correlated and were equally good correlates of insect H. Together they accounted fir 79% of the variance in insect H. This extends to insects a correlation between plant and animal diversity, already well established for birds and possibly true for lizards and rodents. It leaves open the unresolved question as to whether plant structure or plant species diversity is more important.
Thirty samples of ants were taken in each of seven habitats: primary forest, rubber plantation, coffee plantation, oilpalm plantation, kunai grassland, eucalypt savannah and urban grassland. Sixty samples were taken in cocoa plantations. A total of 156 species was taken, and the frequency of occurrence of each in each habitat is given. Eight stenoecious species are suggested as habitat indicators. Habitats fell into a series according to the similarity of their ant faunas: forest, rubber and coffee, cocoa and oilpalm, kunai and savannah, urban. This series represents an artificial, discontinuous succession from a complex stable ecosystem to a simple unstable one. Availability of species suitably preadapted to occupy habitats did not appear to limit species richness. Habitat heterogeneity and stability as affected by human interference did seem to account for inter-habitat variability in species richness. Species diversity was compared between habitats using four indices: Fisher et al.; Margalef; Shannon; Brillouin. Correlation of diversity index with habitat heterogeneity plus stability was good for the first two, moderate for Shannon, and poor for Brillouin. Greatest diversity was found in rubber, the penultimate in the series of habitats according to heterogeneity plus stability ('maturity'). Equitability exceeded the presumed maximum in rubber, and was close to the maximum in all habitats. The mosaic dispersion pattern found among ants elsewhere also appeared to be present in each habitat. The mean maximum number of territories possible to be overlapping is about 4.6; the number in a particular case probably being a function of the specialization of the dominant ant present. Ecological isolating mechanisms among ants are probably similar to those among birds; size and structure of mouthparts in ant communities warrant further study.
Digging-in effects were recorded while using pitfall traps in a study of ants in Southern Australia. These effects consist of high catches immediately after traps are established which subsequently decline. They are most pronounced among ants with nests close, or accessible to traps, but catches of ants from more distant traps may show delayed digging-in effects. It is suggested that the digging-in effect can be reduced by placing pitfalls, inverted, for one week prior to operating them as traps.Les effets d'enfouissement ont t observs en utilisant des piges au cours d'une tude des fourmis du Sud australien. Ces effets consistent en de nombreuses captures, aussitt aprs la mise en place des piges, suivis d'une rduction de ce nombre. Ils sont plus marqus chez les fourmis dont les nids sont proches ou accessibles par rapport aux piges, mais des captures de fourmis dans des piges plus loigns peuvent prsenter des effets retards. Il est suggr que l'effet d'enfouissement peut tre rduit en plaant les trappes renverses une semaine avant de les utiliser comme piges.
Collards were grown at Ithaca, New York, in two experimental habitats: pure stands and single rows that were bounded on each side by diverse, meadow vegetation. The arthropods associated with these plants were sampled on 20 dates over a 3-year period. The status of the herbivore species was measured by their rank in biomass in each sample. The two most prominent species, Phyllotreta cruciferae and Pieris rapae, maintained high status throughout the investigation, but another important species, Brevicoryne brassicae, was absent for an entire season. Pit feeders usually formed the most important herbivore guild. Nevertheless, the guild spectrum, which describes the functional structure of the fauna, varied widely in time and space. The size distributions of species and of individuals were both highly skewed toward the smaller sizes. Herbivore loads, the mean biomass of herbivores per 100 g of consumable foliage, were consistently higher in the pure stands. Moreover, herbivore loads varied significantly with season in each experimental habitat. Both the number of herbivore species and the diversity of the herbivore load were greater in the diverse habitat. Biomass was more heavily concentrated among the prominent herbivores in the pure stands; increased dominance, rather than differences in species richness, appeared to be the major cause for the lower herbivore diversity in this habitat. The diversity of predators and parasitoids was higher in the pure stands. Most of the abundant species found on collards shared a similar narrow range of hosts. As a result the species in this core group of herbivores and parasitoids were regularly associated with each other. Predators and the less abundant herbivores tended to be less specialized and served to link the collard association with the surrounding community. Plant-arthropod associations are representative of component communities, well-integrated systems that form portions of larger compound communities. This distinction facilitates the analysis of community structure. Microclimates and the effectiveness of @'enemies@' did not appear to differ sufficiently in the two experimental habitats to account for the observed differences in the herbivore load. The results suggest a new proposition, the resource concentration hypothesis, which states that herbivores are more likely to find and remain on hosts that are growing in dense or nearly pure stands; that the most specialized species frequently attain higher relative densities in simple environments; and that, as a result, biomass tends to become concentrated in a few species, causing a decrease in the diversity of herbivores in pure stands.
Since its introduction to Bermuda in 1953, Iridomyrnex humilis has expanded steadily, replacing Pheidole megacephala in all habitats. The basis for this competition was not determined. The dispersal rates of Iridomyrmex from 1953-1966 are analyzed. From 1953 to 1959, Iridomyrmex increased its distribution at the rate of 394 ha. per year. However, radius did not increase linearly, and it is suggested that only those foci within a critical distance of the perimeter can colonize new areas. Moreover, after 1959 there was a decrease in both number of new foci and growth of individual foci. Therefore, while Iridomyrmex and Pheidole have not established an equilibrium, the rate of replacement has slowed markedly.
Some effects of fire frequenC)' onji'llhos at J onkershoek
- Van Wi Lg
- B W En
VAN WI LG EN, B. W. tg8o. Some effects of fire frequenC)' onji'llhos at J onkershoek, Stellenbosch, South
Africa. ~1.S c. thesis, 126 pp., Unive rsity of Capr Town.
Rates of competiti ve ex clusion by th e Argentin e ant in Bermuda
CROWELL, K. L. 1968. Rates of competiti ve ex clusion by th e Argentin e ant in Bermuda. Ecology
49(3): 5:i I -55:) ·
Hymenoptera In: Biogeograph)' and Ecology of Southern Africa
- Pri Ns
PRI NS, A. J. 1978. Hymenoptera. In: Biogeograph)' and Ecology of Southern Africa. Ed. M. J. A.