Thinandavha C. Munyai

Climate mediates the effects of disturbance on ant assemblage structure

Many studies have focused on the impacts of climate change on biological assemblages, yet little is known about how climate interacts with other major anthropogenic influences on biodiversity, such as habitat disturbance. Using a unique global database of 1128 local ant assemblages, we examined whether climate mediates the effects of habitat disturbance on assemblage structure at a global scale. Species richness and evenness were associated positively with temperature, and negatively with disturbance. However, the interaction among temperature, precipitation and disturbance shaped species richness and evenness. The effect was manifested through a failure of species richness to increase substantially with temperature in transformed habitats at low precipitation. At low precipitation levels, evenness increased with temperature in undisturbed sites, peaked at medium temperatures in disturbed sites and remained low in transformed sites. In warmer climates with lower rainfall, the effects of increasing disturbance on species richness and evenness were akin to decreases in temperature of up to 9°C. Anthropogenic disturbance and ongoing climate change may interact in complicated ways to shape the structure of assemblages, with hot, arid environments likely to be at greatest risk.

GlobalAnts: a new database on the geography of ant traits (Hymenoptera: Formicidae)

In recent years the focus in ecology has shifted from species to a greater emphasis on functional traits. In tandem with this shift, a number of trait databases have been developed covering a range of taxa. Here, we introduce the GlobalAnts database. Globally, ants are dominant, diverse and provide a range of ecosystem functions. The database represents a significant tool for ecology in that it (i) contributes to a global archive of ant traits (morphology, ecology and life history) which complements existing ant databases and (ii) promotes a trait‐based approach in ant and other insect ecology through a broad set of standardised traits. The GlobalAnts database is unique in that it represents the largest online database of functional traits with associated georeferenced assemblage‐level data (abundance and/or occupancy) for any animal group with 9056 ant species and morphospecies records for entire local assemblages across 4416 sites. We describe the structure of the database, types of traits included and present a summary of data coverage. The value of the database is demonstrated through an initial examination of trait distributions across subfamilies, continents and biomes. Striking biogeographic differences in ant traits are highlighted which raise intriguing questions as to the mechanisms generating them.

A global database of ant species abundances

What forces structure ecological assemblages? A key limitation to general insights about assemblage structure is the availability of data that are collected at a small spatial grain (local assemblages) and a large spatial extent (global coverage). Here, we present published and unpublished data from 51 ,388 ant abundance and occurrence records of more than 2,693 species and 7,953 morphospecies from local assemblages collected at 4,212 locations around the world. Ants were selected because they are diverse and abundant globally, comprise a large fraction of animal biomass in most terrestrial communities, and are key contributors to a range of ecosystem functions. Data were collected between 1949 and 2014, and include, for each geo-referenced sampling site, both the identity of the ants collected and details of sampling design, habitat type, and degree of disturbance. The aim of compiling this data set was to provide comprehensive species abundance data in order to test relationships between assemblage structure and environmental and biogeographic factors. Data were collected using a variety of standardized methods, such as pitfall and Winkler traps, and will be valuable for studies investigating large-scale forces structuring local assemblages. Understanding such relationships is particularly critical under current rates of global change. We encourage authors holding additional data on systematically collected ant assemblages, especially those in dry and cold, and remote areas, to contact us and contribute their data to this growing data set.

Temporal patterns of ant diversity across a mountain with climatically contrasting aspects in the tropics of Africa.

Factors that drive species richness over space and time are still poorly understood and are often context specific. Identifying these drivers for ant diversity has become particularly relevant within the context of contemporary global change events. We report on a long-term bi-annual (wet and dry seasons), standardized sampling of epigeal ants over a five year period on the mesic and arid aspects of an inselberg (Soutpansberg Mountain Range) in the tropics of Africa. We detail seasonal, annual and long-term trends of species density, test the relative contribution of geometric constraints, energy, available area, climate, local environmental variables, time, and space in explaining ant species density patterns through Generalized Linear Mixed Models (GLMM) where replicates were included as random factors to account for temporal pseudo-replication. Seasonal patterns were very variable and we found evidence of decreased seasonal variation in species density with increased elevation. The extent and significance of a decrease in species density with increased elevation varied with season. Annual patterns point to an increase in ant diversity over time. Ant density patterns were positively correlated with mean monthly temperature but geometric constraints dominated model performance while soil characteristics were minor correlates. These drivers and correlates accounted for all the spatio-temporal variability in the database. Ant diversity was therefore mainly determined by geometric constraints and temperature while soil characteristics (clay and carbon content) accounted for smaller but significant amounts of variation. This study documents the role of season, elevation and their interaction in affecting ant species densities while highlighting the importance of neutral processes and temperature in driving these patterns.

Dominance-diversity relationships in ant communities differ with invasion

The relationship between levels of dominance and species richness is highly contentious, especially in ant communities. The dominance-impoverishment rule states that high levels of dominance only occur in species-poor communities, but there appear to be many cases of high levels of dominance in highly diverse communities. The extent to which dominant species limit local richness through competitive exclusion remains unclear, but such exclusion appears more apparent for non-native rather than native dominant species. Here we perform the first global analysis of the relationship between behavioral dominance and species richness. We used data from 1,293 local assemblages of ground-dwelling ants distributed across five continents to document the generality of the dominance-impoverishment rule, and to identify the biotic and abiotic conditions under which it does and does not apply. We found that the behavioral dominance-diversity relationship varies greatly, and depends on whether dominant species are native or non-native, whether dominance is considered as occurrence or relative abundance, and on variation in mean annual temperature. There were declines in diversity with increasing dominance in invaded communities, but diversity increased with increasing dominance in native communities. These patterns occur along the global temperature gradient. However, positive and negative relationships are strongest in the hottest sites. We also found that climate regulates the degree of behavioral dominance, but differently from how it shapes species richness. Our findings imply that, despite strong competitive interactions among ants, competitive exclusion is not a major driver of local richness in native ant communities. Although the dominance-impoverishment rule applies to invaded communities, we propose an alternative dominance-diversification rule for native communities.

Changes in landuse alter ant diversity, assemblage composition and dominant functional groups in African savannas

Africa’s savannas are undergoing rapid conversion from rangelands into villages and croplands. Despite limited research, and evidence of deleterious effects to biodiversity, international organisations have earmarked this system for cropland. Invertebrates, and ants in particular, are sensitive indicators of habitat fragmentation, and contribute to ecosystem services at a range of scales. We investigated how rangelands, villages and croplands differ in ant species and functional diversity, and assemblage composition. We sampled ants using pitfall traps at 42 sites (14 replicates each in rangeland, cropland, and village) in northern South African savannas. We investigated the impact of landuse, season, and multiple soil and vegetation habitat variables on ant species diversity, assemblages and functional diversity. Rangelands had the greatest ant species richness, particularly in the wet season. Richness declined with increasing soil clay content. Ant assemblages were distinctly different between landuse types. Rangeland harboured the widest diversity of indicator species, and contained greatest functional diversity. Rangelands accommodated more scavengers, granivores, and plant-matter feeders than cropland, and representation of these groups varied with season. Ants play essential roles in soil nutrient cycling, plant and seedling recruitment, and impact other arthropods through predation and aphidoculous behaviour that in turn influences entire food webs. Thus, the reduced species richness, changes in assemblage composition and the loss of functional groups in ant assemblages found in cropland and villages is potentially problematic. Left unchallenged, these new forms of landuse threaten to characterise the entire African savanna system, impacting not only future ecological, but possibly also human wellbeing.

Animal taxa contrast in their scale-dependent responses to land use change in rural Africa

Human-dominated landscapes comprise the bulk of the world’s terrestrial surface and Africa is predicted to experience the largest relative increase over the next century. A multi-scale approach is required to identify processes that maintain diversity in these landscapes. Here we identify scales at which animal diversity responds by partitioning regional diversity in a rural African agro-ecosystem between one temporal and four spatial scales. Human land use practices are the main driver of diversity in all seven animal assemblages considered, with medium sized mammals and birds most affected. Even the least affected taxa, bats and non-volant small mammals (rodents), responded with increased abundance in settlements and agricultural sites respectively. Regional turnover was important to invertebrate taxa and their response to human land use was intermediate between that of the vertebrate extremes. Local scale (< 300 m) heterogeneity was the next most important level for all taxa, highlighting the importance of fine scale processes for the maintenance of biodiversity. Identifying the triggers of these changes within the context of functional landscapes would provide the context for the long-term sustainability of these rapidly changing landscapes.

Landuse Change in Savannas Disproportionately Reduces Functional Diversity of Invertebrate Predators at the Highest Trophic Levels: Spiders as an Example

Abstract Predators play a disproportionately positive role in ensuring integrity of food webs, influencing ecological processes and services upon which humans rely. Predators tend to be amongst the first species to be affected by anthropogenic disturbance, however. Spiders impact invertebrate population dynamics and stabilise food webs in natural and agricultural systems (potentially mitigating against crop pests and reduced yields). Africa’s savannas are undergoing continent-wide conversion from low-density rangelands to villages and croplands, as human populations burgeon. Despite limited research, and evidence of deleterious impacts to biodiversity, African savannas are earmarked by prominent international organisations for conversion to cropland. Given the key role of spiders in food webs, they can have beneficial impacts in agroecosystems. Furthermore, functional diversity (FD) reflects ecosystem pattern and processes better than species diversity, so we evaluated impacts of large-scale landuse change on both species richness and FD. We surveyed spiders using pitfall traps at 42 sites (14 replicates each in rangeland, cropland, and villages) in South African savannas, investigating effects of landuse, season, and habitat variables on spider species diversity and FD. Species richness was lowest in villages. FD was lowest in cropland, however, with reduced representation of traits associated with hunting of larger invertebrates. Furthermore, there were fewer specialists in croplands. These findings suggest that even when cropland does not impact species diversity, loss of FD can still occur. As savanna systems transform, impacts on invertebrate population dynamics may increase the possibility of a breakdown in pest control in natural and agricultural systems, given changes in FD of invertebrate predators.

Laboratory studies on the biology and host range of Dichrorampha odorata (Lepidoptera: Tortricidae), a biological control agent for Chromolaena odorata (Asteraceae)

ABSTRACT Dichrorampha odorata (Lepidoptera: Tortricidae) is a moth from Jamaica whose larvae bore into, and kill, the shoot tips of the invasive alien plant, Chromolaena odorata (L.) King and Robinson (Asteraceae). This study reports aspects of the biology of D. odorata, and also determined the host specificity (larval and adult no-choice trials) of the moth. Adults were short lived (ranging from 2 to 7 days), with females laying a mean of 15.4 eggs. Eggs took 9 days to hatch, larvae 20–23 days to develop and the pupal stage lasted 11–12 days, giving an overall lifecycle period of 41–45 days. Larval no-choice tests using 34 asteraceous test species indicated that only C. odorata could sustain complete development of D. odorata to adulthood, although there was slight initial boring 14 test species (plus chromolaena). Results from the adult nochoice trials, in which seven test-plant species were exposed to D. odorata, were consistent with those from larval trials, with larval damage, pupae and adults of D. odorata recorded from only C. odorata. This confirmed that only C. odorata is a suitable host for D. odorata in South Africa. Permission has subsequently been granted for the release of D. odorata in South Africa, thus making it the first shoot-tip attacking agent to be released against C. odorata. It is hoped that in the field, high levels of damage by the moth will reduce the height and therefore competitiveness of C. odorata, thereby contributing to the success of biological control of this plant.