Maitland Seaman

Species sorting in space and time—the impact of disturbance regime on community assembly in a temporary pool metacommunity

Abstract Ecosystems generally are not stable over long periods of time and are subject to disturbances of different frequencies and intensities. As a result, natural communities usually are not in equilibrium, and temporal snapshots can show different stages of community assembly. Nonequilibrium is especially common in temporary aquatic systems where desiccation continuously resets the development of communities and hydroperiod is an important determinant of species richness and community structure. We investigated effects of disturbance regime on community assembly of aquatic invertebrates in a cluster of 36 temporary rock pools in central South Africa. Pools were assigned to 4 categories based on their long-term disturbance regime and were sampled 4 times during 1 inundation. Disturbance modulated the relative importance of deterministic and stochastic processes driving community assembly and reduced both α and β diversity. Premature desiccation truncated community development. Initial communities were dominated by resident large branchiopods (fairy shrimp and clam shrimp). Arrival of flying colonists, including many predators, caused a drastic change in community composition and initiated a new successional phase dominated by cladocerans. For residents, the link between local environment and community structure was strongest early during inundation and decreased during community assembly. For flying colonists, variation in arrival time and habitat selection led to a better match between communities and environment later during inundation. We conclude that the combination of colonization–extinction dynamics and niche partitioning in space and time determines metacommunity structure in this extreme type of aquatic habitat.

Hatching phenology, life history and egg bank size of fairy shrimp Branchipodopsis spp. (Branchiopoda, Crustacea) in relation to the ephemerality of their rock pool habitat

In temporary aquatic habitats, permanence and the severe disturbance associated with desiccation are strong selective agents expected to lead to differentiation in life history strategies in populations experiencing different disturbance regimes. Besides optimal timing of hatching of dormant life stages, maturation and reproduction, pool inhabitants also benefit from the acquisition of reliable cues for the quality of the ambient environment. We investigated whether hatching patterns, life history characteristics and egg bank size of Branchipodopsis fairy shrimp (Branchiopoda, Anostraca) inhabiting a cluster of temporary rock pools in South Africa reflect variation in habitat stability and hatching cues. Long-term hydrological variation was used to select pools along a gradient of habitat stability. Initial conductivity was a good indicator for the length of inundations. No hatching occurred under elevated conductivities, which may present a mechanism to avoid abortive hatching. Egg bank size was unaffected by habitat size or habitat stability but instead was related to cover by a protective sheet of dry aquatic vegetation, which presumably counteracts egg bank erosion by wind when pools are dry. Life history but not hatching phenology reflected some aspects of habitat stability. Fairy shrimp populations in ephemeral pools started reproduction earlier than populations in more stable habitats. Additional common garden or transplant experiments, however, will be required to assess the relative importance of environmental and genetic components in explaining the observed variation and acquire more insight into the trade-offs that lie at the base of the evolution of life history strategies along the pond permanence gradient.

Branchipodopsis species — specialists of ephemeral rock pools

The anostracan Branchipodopsis genus is widespread throughout southern Africa and is the second most speciose anostracan taxon in this sub-continent. Branchipodopsis species are particularly dominant in small short-lived and clear rock pools, to the vagaries of which they are extremely well adapted. Such rock pools were studied in the Drakensberg region, in the eastern Free State and in south-eastern Botswana. Common features of Branchipodopsis-inhabited rock pools are the transparency of the water and the very low conductivity values (generally below 50μScm−1, often less than 10μScm−1). These shallow (usually less than 50cm) water bodies with limited buffering capacity show major fluctuations in pH values (often between about pH 4 and 11), depending on the time of the day and the stage in the hydrocycle. Rock pools also closely follow ambient air temperatures with resulting fluctuations of values between 10 and 40°C. Depending on local climatic conditions, small rock pools are usually short-lived and have several wet/dry cycles during one rainy season. Branchipodopsis species are the record-holders in this race against time with maturation usually being reached within the first week after inundation. Broods of resting eggs are generally small (less than 80 eggs) but are produced almost daily. Often (in 30% of cases in south-eastern Botswana), erratic rainfall does not allow sufficient time for successful maturation and reproduction. As a safe-guarding mechanism in B. wolfi in south-eastern Botswana, only some of the eggs hatch on each occasion, depending on environmental conditions, thus extending the chances for successful recruitment. While short-range dispersal of floating eggs by overflows is common, long-range dispersal (e.g. by wind) seems to be rare and to be restricted to shallow pools with little vegetation. Limited effective dispersal may explain the high number of endemic species (e.g. four in the Drakensberg region) and the large morphological variation in some widespread species such as B. wolfi.

Long Distance Dispersal of Zooplankton Endemic to Isolated Mountaintops - an Example of an Ecological Process Operating on an Evolutionary Time Scale

Recent findings suggest a convergence of time scales between ecological and evolutionary processes which is usually explained in terms of rapid micro evolution resulting in evolution on ecological time scales. A similar convergence, however, can also emerge when slow ecological processes take place on evolutionary time scales. A good example of such a slow ecological process is the colonization of remote aquatic habitats by passively dispersed zooplankton. Using variation at the protein coding mitochondrial COI gene, we investigated the balance between mutation and migration as drivers of genetic diversity in two Branchipodopsis fairy shrimp species (Crustacea, Anostraca) endemic to remote temporary rock pool clusters at the summit of isolated mountaintops in central South Africa. We showed that both species colonized the region almost simultaneously c. 0.8 My ago, but exhibit contrasting patterns of regional genetic diversity and demographic history. The haplotype network of the common B. cf. wolfi showed clear evidence of 11 long distance dispersal events (up to 140 km) with five haplotypes that are shared among distant inselbergs, as well as some more spatially isolated derivates. Similar patterns were not observed for B. drakensbergensis presumably since this rarer species experienced a genetic bottleneck. We conclude that the observed genetic patterns reflect rare historic colonization events rather than frequent ongoing gene flow. Moreover, the high regional haplotype diversity combined with a high degree of haplotype endemicity indicates that evolutionary- (mutation) and ecological (migration) processes in this system operate on similar time scales.

Functional Feeding Groups as a Taxonomic Surrogate for a Grassland Arthropod Assemblage

ABSTRACT Considering the precarious conservation status of the grassland biome in South Africa, effective assessment and monitoring is imperative. The potential use of terrestrial arthropods in ecological assessment has received much attention, but little headway has been made in formulating standardised bioassessment protocols. A suggested reason for this lack of progress is the high diversity of terrestrial arthropods and the high taxonomic expertise required. Sampling was carried out across 12 months in the Bloemfontein Dry Grassland vegetation type and the potential of using functional feeding groups (FFG) as taxonomic surrogates for family level arthropods was investigated. An F-test associated with an analysis of covariance (ANCOVA) found a significant correlation between FFG and families for measures of richness, Shannon and Simpson diversity. Accumulation curves indicated that a higher proportion of FFG than families could be assessed with the same sampling intensity. Both families and FFG best fitted the stochastic normal and geometric series relative abundance distribution models, implying that there is no distinction between the taxonomic units with regard to abundance distributions. The reality remains that information does become lost when using surrogacy, so there will continue to be a need for specialist ecological proficiency for the highest risk assessments. It was concluded that for rapid monitoring and snap-shot assessments, FFG could be used as a valuable and reliable taxonomic surrogate.

Occurrence and abundance of waterbirds at an ephemeral pan in the Northern Cape Province, South Africa

Bi-monthly counts of waterbirds were made between March and September 2003 at an ephemeral pan in the Northern Cape Province following the first substantial inundation since 1988. Bi-annual counts between 1991 and 2003 indicated that the pan infrequently supported waterbirds, with waterfowl and small waders generally being the dominant species. During the bimonthly counts, a total of 50 waterbird species was recorded, with the most dominant species, both in terms of numbers and duration of presence, being Black-winged Stilt Himantopus himantopus (max. 378), Cape Shoveller Anas smithii (max. 260) and South African Shelduck Tadorna cana (max. 200). Most other waterfowl and wader species were regular but in lower numbers. Species groups that occurred in limited numbers or for short periods include primarily herons, grebes, flamingos, ibises and storks. Species abundance and richness reached a peak one month after the pan was inundated, followed by a gradual decline over the ensuing two months.

Evidence of Island Effects in South African Enterprise Ecosystems

Living organisms and business enterprises (hereafter the term enterprise will be used to refer to a business enterprise) exhibit certain similarities. Beinhocker (2006) stated that: “Economic wealth and biological wealth are thermodynamically the same sort of phenomena, and not just metaphorically. Both are systems of locally low entropy, patterns of order which evolved over time under the constraint of fitness functions. Both are forms of fit order.” He added that organisms and business enterprises are both subjected to Darwinian-type competition. Based on the foregoing reasoning we proposed that there should be similarities between natural ecosystems and enterprise ecosystems as described by Toerien & Seaman (2010).

A PARTICIPATORY SUSTAINABILITY ASSESSMENT PROCESS FOR BIODIVERSITY CONSERVATION IN LESOTHO

Sustainability assessment processes are increasingly being applied towards integration of the sustainability agenda within diverse decision-making jurisdictions. This paper seeks to contribute insights from a process undertaken within rural areas in Lesotho. A learning-by-doing and people-centred approach was explored within a qualitative multiple case study to integrate biodiversity considerations within the broader livelihoods sustainability context. Stakeholders collectively determined interpretations, aspirations and priorities for action planning and pathways that sustain biodiversity. This process yielded a functional context-specific sustainability assessment framework to guide stakeholders when embarking on biodiversity interventions that enhance supply of ecosystem services in and outside protected areas. However, the effectiveness of the process requires that it should be nested within an enabling environment characterised by relevant international and national biodiversity policy and strategic frameworks, decision- making structures, funding, tools and expertise, sensitisation and capacity-building.

Invertebrates or Iron: Does Large-Scale Opencast Mining Impact Invertebrate Diversity In Ephemeral Wetlands?

Disturbance has been offered as an explanatory mechanism in structuring the variation of species across a landscape. In this study, we investigated the effect of the impact by Kolomela Iron Mine on the variation of species occurring in temporary pans. Using a novel null model approach to partitioning two sets of data (from before and after the establishment of the mine) into independent alpha (&agr;) and beta (&bgr;) components, we determined that the mining practices have had little to no impact on the invertebrate diversity. This suggests that these communities were more resilient than previously assumed. The results were, however, confounded by the fact that the resting eggs of pan inhabitants could remain dormant in the sediment for decades; suggesting that observed diversity patterns were possibly remnants of unknown past events. To ensure that the effects of present-day impacts are assessed, continuous monitoring is recommended. Similarly, the preservation of conservation areas and a landscape wide management system were proposed to ensure that large-scale ecological process are not jeopardized by the gradual fragmentation of the pan metacommunity.

Intra-annual variation of arthropod-plant interactions and arthropod trophic structure in an endangered grassland in the Free State province, South Africa

Arthropods are valuable biological indicators owing to strong relationships with primary producers. The supposition that arthropod-plant interactions are constant over seasons was tested using Mantel tests on correlations between these groups. A total of 78 plant species and 108 arthropod families were sampled monthly from the endangered Bloemfontein Dry Grassland at the Free State National Botanical Gardens between April 2009 and March 2010. Interaction strengths between plants and arthropods varied within a calendar year; being strongest in winter months (July and August), initiation of the growth season (November) and peak growth season (February and March). It was hypothesised that variation was caused by changing primary productivity. The trophic composition of the arthropod community supported this hypothesis as the ratio between primary consumers (herbivores) and secondary consumers (predators and parasitoids) showed patterns that coincided with periods of strong arthropod-plant interactions. Patterns were explained by multiple theories linking plant and arthropod diversity. It was concluded that arthropod assemblages are closely linked to primary producers, the abiotic environment and top-down trophic forces at different times of the year. Future arthropod-based studies should be performed with clear objectives and seasonal benchmark conditions to overcome these variations.