Increasing representation of localized dung beetles across a chronosequence of regenerating vegetation and natural dune forest in South Africa

Abstract

Aim Species assemblages with high proportions of localized taxa occur in regional islands with a history of strong eco‐climatic separation from adjacent systems. Current disturbance in such islands of relictualism or endemism disrupts the distinctive local character in favour of regionally distributed taxa with a wider range of tolerances. However, rehabilitation of the system should restore the localized biota. Thus, we used biogeographical composition to assess progress towards restoration of the dung beetle fauna associated with such an island of endemism following dredge‐mining. Location The study was conducted in natural coastal dune forest and a 23‐year chronosequence of regenerating dune vegetation in the Maputaland centre of endemism, KwaZulu‐Natal, South Africa. Methods Dung beetles were trapped in eight stands of regenerating vegetation of different ages (< 1 year to ~21 years) and in four stands of natural dune forest with differing ecological characteristics defined by measurements of vegetative physiognomy and microclimate. Species groups defined from multivariate analysis of biogeographical distribution patterns and vegetation associations were used to demonstrate quantitative compositional changes in the dung beetle assemblages across the chronosequence to natural forest. Results Three biogeographical groups were defined. One group comprised species widespread in southern Africa or both southern and east Africa. The other two groups were endemic, one to the east coast and the other to Maputaland. There was a general trend from dominance by regionally distributed dung beetle taxa to dominance by locally distributed taxa across the chronosequence of regenerating vegetation from grassland, to open Acacia karroo thicket, to dense A. karroo‐dominated woodland. However, this trend was linked closely to the relative physiognomic and microclimatic similarity between the regenerating vegetation and natural forest. Thus, proportions of locally distributed taxa were lower in older chronosequence woodland (~18–~21 years) with its low canopy cover and open understorey than in dense early chronosequence woodland (~9–~12 years), which is physiognomically and microclimatically closer to species‐diverse natural forest with its dense canopy and understorey. Overall, the present dung beetle community comprises five species groups. Single widespread (21 spp.) and endemic groups (14 spp.) showed similar patterns of association with early chronosequence grassland and open thicket stands. A single widespread (3 spp.) and two endemic shade‐associated groups (3 and 11 spp.) showed differing patterns of association centred, respectively, in late chronosequence woodland, natural forest, or all shaded stands. Main conclusions At 23 years, vegetative regeneration is still at an early stage, but abundant activity of most, although not all species recorded in natural forest, is recovered with the closure of the woodland canopy at ~9 years. Compositional differences with respect to natural forest vary closely with vegeta...

Is microclimate-driven turnover of dung beetle assemblage structure in regenerating coastal vegetation a precursor to re-establishment of a forest fauna?

“…This flightless Maputaland endemic was also absent from a relatively isolated, probably formerly disturbed, forest patch studied by Davis et al (2002;2003). Due to flightlessness, it may not be able to re-colonize rehabilitated sites if they are isolated from an undisturbed source forest by disturbed terrain.…”

“…In 2000, three study sites were selected in each of four forest patches (12 study sites) and in each of eight age windows across a 23 year chronosequence of rehabilitating vegetation (24 study sites) (Davis et al 2002;2003).…”

“…For purposes of comparison, the present survey followed a similar design to that used in 2000 (Davis et al 2002;2003). The 2010 survey sampled dung beetles from 36 study sites in the two forest patches and ten age windows of rehabilitating vegetation, three study sites per window.…”

“…Compared to the earlier survey (Davis et al 2002;2003), trap emplacement was the same at all study sites and age windows except in the early succession where, in 2010, traps were placed along pathways cut into the edge of the dense shrubland (Window 9) or woodland (Window 7) rather than primarily in spaces between patches of dense shrubland as in 2000 (Windows 6y, 6o). Despite recommendations for a minimum between-trap distance of 50 m (Larsen and Forsyth 2005), traps were emplaced 10 m apart to be consistent with the methods used in 2000.…”

“…The results were used to determine proportional bias of species abundance to shade or non-shaded conditions in each cluster. With modifications, the biogeographical classification of Davis et al (2002) was used to determine proportional bias within each cluster to three different biogeographical patterns. Modifications were necessary as, during the course of the 2010 study, several species formerly classified as Maputaland endemics (Davis et al 2002) The ordination of species abundance patterns (63 species, 50 606 individuals) classified the study sites into a maximum of four different clusters (Table 1, Fig.…”