Caswell Munyai

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

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,

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.

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 biannual
(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.
Introduction

Mountains are biodiversity hotspots and provide
spatially compressed versions of regional and continental
variation. They might be the most cost effective way
to measure the environmental associations of regional
biotic communities and their response to global climate
change. We investigated spatial variation in epigeal ant
diversity along a north–south elevational transect over the
Soutpansberg Mountain in South Africa, to see to what
extent these patterns can be related to spatial (regional) and
environmental (local) variables and how restricted taxa are
to altitudinal zones and vegetation types. A total of 40,294
ants, comprising 78 species were caught. Ant richness
peaked at the lowest elevation of the southern aspect but
had a hump-shaped pattern along the northern slope. Species
richness, abundance and assemblage structure were
associated with temperature and the proportion of bare
ground. Local environment and spatially structured environmental
variables comprised more than two-thirds of the
variation explained in species richness, abundance and
assemblage structure, while space alone (regional processes)
was responsible for\10%. Species on the northern
aspect were more specific to particular vegetation types,
whereas the southern aspect’s species were more generalist.
Lower elevation species’ distributions were more
restricted. The significance of temperature as an explanatory
variable of ant diversity across the mountain could
provide a predictive surrogate for future changes. The
effect of CO2-induced bush encroachment on the southern
aspect could have indirect impacts complicating prediction,
but ant species on the northern aspect should move uphill at
a rate proportional to their thermal tolerance and the
regional increases in temperature. Two species are identified
that might be at risk of local extinction.