Browsing by Author "Simaika, John P."

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    A comparative analysis reveals weak relationships between ecological factors and beta diversity of stream insect metacommunities at two spatial levels
    (John Wiley & Sons Ltd., 2015-02-23) Heino, Jani; Melo, Adriano S.; Bini, Luis Mauricio; Altermatt, Florian; Al-Shami, Salman A.; Angeler, David G.; Bonada, Nuria; Brand, Cecilia; Callisto, Marcos; Cottenie, Karl; Dangles, Olivier; Dudgeon, David; Encalada, Andrea; Gothe, Emma; Gronroos, Mira; Hamada, Neusa; Jacobsen, Dean; Landeiro, Victor L.; Ligeiro, Rapael; Martins, Renato T.; Miserendino, Maria Laura; Rawi, Che Salmah Md; Rodrigues, Marciel E.; Roque, Fabio de Oliveira; Sandin, Leonard; Schmera, Denes; Sgarbi, Luciano F.; Simaika, John P.; Siqueira, Tadeu; Thompson, Ross M.; Townsend, Colin R.
    The hypotheses that beta diversity should increase with decreasing latitude and increase with spatial extent of a region have rarely been tested based on a comparative analysis of multiple datasets, and no such study has focused on stream insects. We first assessed how well variability in beta diversity of stream insect metacommunities is predicted by insect group, latitude, spatial extent, altitudinal range, and dataset properties across multiple drainage basins throughout the world. Second, we assessed the relative roles of environmental and spatial factors in driving variation in assemblage composition within each drainage basin. Our analyses were based on a dataset of 95 stream insect metacommunities from 31 drainage basins distributed around the world. We used dissimilarity-based indices to quantify beta diversity for each metacommunity and, subsequently, regressed beta diversity on insect group, latitude, spatial extent, altitudinal range, and dataset properties (e.g., number of sites and percentage of presences). Within each metacommunity, we used a combination of spatial eigenfunction analyses and partial redundancy analysis to partition variation in assemblage structure into environmental, shared, spatial, and unexplained fractions. We found that dataset properties were more important predictors of beta diversity than ecological and geographical factors across multiple drainage basins. In the within-basin analyses, environmental and spatial variables were generally poor predictors of variation in assemblage composition. Our results revealed deviation from general biodiversity patterns because beta diversity did not show the expected decreasing trend with latitude. Our results also call for reconsideration of just how predictable stream assemblages are along ecological gradients, with implications for environmental assessment and conservation decisions. Our findings may also be applicable to other dynamic systems where predictability is low.
  • Thumbnail Image
    Item
    Conservation biogeography of South African dragonflies (Odonata)
    (Stellenbosch : Stellenbosch University, 2008-12) Simaika, John P.; Samways, Michael J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    The great pressures on freshwaters require their conservationists and managers to develop methods to rapidly and accurately assess their condition. Dragonflies are excellent indicators of habitat integrity and are effective organisms for this purpose. However, assessment must be done at the correct spatial scale. My aim here is to optimize the spatial resolution at which species are mapped, using three different concepts and methods in freshwater invertebrate distribution mapping, with special emphasis on IUCN Red Listing. The first is the extent of occurrence (EOO) concept, using the minimum convex polygon, and the second, the area of occupancy (AOO) concept, using IUCN and quaternary catchments. The third approach uses a river layer to compare the suitability of grids as opposed to catchments in mapping. In this study I found that area estimation based on minimum convex polygons should not be encouraged for aquatic organisms. This study also suggests that the IUCN concept of area of occupancy (AOO) should be redefined simply as occurrence, referring to known point-locality presences only and, if future data allow, to known absences. The IUCN extent of occurrence (EOO), for aquatic species, should be defined as ‘the sum of the smallest hydrological units identified of presently known, inferred or projected occurrences of a taxon, excluding cases of vagrancy, that are used to estimate the threat to a taxon’. A single hydrological unit is also the conservation or management unit. Currently, that unit is the quaternary catchment. Dragonflies have excellent potential as indicators of habitat integrity. For this purpose, my aim was to develop the Dragonfly Biotic Index (DBI) for South Africa and compare the DBI to another index, the Average Taxonomic Distinctness Index (AvTD), which was believed to have potential in assessments. The DBI and AvTD are correlated, which suggests that they could be used on a complementary basis to prioritize sites. The DBI is a low-cost, easy-to-use method and is already used for measuring habitat recovery. It has great potential for environmental assessment and monitoring freshwater biodiversity, especially as a complement to freshwater quality assessments that use macroinvertebrate scores. I thus recommend its integration into freshwater management and conservation schemes.
  • Thumbnail Image
    Item
    An easy-to-use index of ecological integrity for prioritizing freshwater sites and for assessing habitat quality
    (Springer Verlag, 2009-05) Simaika, John P.; Samways, Michael J.
    Prioritizing and assessing the condition of sites for conservation action requires robust and ergonomic methodological tools. We focus here on prioritizing freshwater sites using two promising biodiversity indices, the Dragonfly Biotic Index (DBI) and Average Taxonomic Distinctness (AvTD). The AvTD had no significant association with either species richness or endemism. In contrast, the DBI was highly significantly associated with species richness and endemism, although the strengths of the associations were weak. These associations are related to how the sub-indices in the DBI are weighted, and how species are distributed geographically. Additionally, the DBI was found to be very useful for site selection based on its ability to measure ecological integrity, combined with level of threat, at multiple spatial scales. The AvTD was found to be useful principally for regional use. As the DBI is a low-cost, easy-to-use method, it has the additional use as a method for assessing habitat quality and recovery in restoration programs. The DBI operates at the species level, and is therefore highly sensitive to habitat condition and has great potential for environmental assessment and monitoring freshwater biodiversity and quality. Practical, worked examples of river restoration are given here. In view of the ease and versatility by which the DBI can be employed, we recommend its testing and possible integration into freshwater management and conservation schemes elsewhere in the world. © 2008 Springer Science+Business Media B.V.
  • Thumbnail Image
    Item
    Predicted range shifts of dragonflies over a wide elevation gradient in the southern hemisphere
    (University of Chicago Press, 2015) Simaika, John P.; Samways, Michael J.
    Human-induced climate change is among the greatest threats to biodiversity, especially when coupled with habitat destruction. For an already water-stressed country like South Africa, changes in temperature and precipitation regimes, coupled with increasing water demands, are likely to lead to losses in biodiversity. Dragonflies are a well-studied surrogate taxon for aspects of freshwater biodiversity. We created species distribution models for 14 dragonfly species, and predicted the changes in species richness, extent of occurrence, and habitat suitability for the years 2050 and 2080 in South Africa, a poorly studied area for range-change predictions for insects. Model predictions for 2 different emissions scenarios suggest that at least 2 species will be lost from the area by 2050, and 3 by 2080. All are widespread Afrotropical species, but with narrow elevation ranges in South Africa. Only 1 species is predicted to benefit greatly from climate change. The remaining species are predicted to persist with reduced extents of occurrences at higher elevations. Most species we studied (12 of 14) thrive in artificial environments. Therefore, to a certain extent, loss in connectivity is unlikely to play a role for these species. However, the 2 stream specialists that occur in the area are particularly vulnerable because of loss of habitat. Species that currently occur farther north in southern Africa and South Africa also are likely to move southward in the future. Thus, species richness may not necessarily decrease, but replacement of species within communities will be significant.
  • Thumbnail Image
    Item
    Species turnover in plants does not predict turnover in flower-visiting insects
    (PeerJ, 2018) Simaika, John P.; Samways, Michael J.; Vrdoljak, Sven M.
    Congruence between plant and insect diversity is considered possibly useful in conservation planning, as the better known plants could be surrogates for the lesser known insects. There has been little quantification of congruence across space, especially in biodiversity rich areas. We compare here species richness, and turnover relationships between plants and flower-visiting insects across space (0.5–80 km) in natural areas of a biodiversity hotspot, the Greater Cape Floristic Region, South Africa. A total of 22,352 anthophile individuals in 198 species and 348 plant species were sampled. A comparison between the plants and anthophiles suggest significant concordance between the two assemblages. However, turnover was weaker in plants than in anthophiles. Plant turnover decreased with greater geographical distance between plot pairs. In contrast, insect turnover remained high with increasing geographical distance between plot pairs. These findings suggest that while patterns of plant diversity and distribution shape flower-visiting insect assemblages, they are not reliable surrogates. The conservation significance of these results is that specialist mutualisms are at greatest risk, and that set-asides on farms would help improve the functional connectivity leading to the maintenance of the full range of mutualisms.