Spider responses to alien plant invasion: the effect of short‐ and long‐term Chromolaena odorata invasion and management

Abstract

1.Invasions by alien plants into unspoiled ecosystems are a cause for concern because the pristine systems are important stores of biodiversity. Indeed, the introduction of non-indigenous species into protected areas is a direct threat to conservation. Consequently, it is fundamental to document the impact that alien invasive plants have on native communities and to determine if, and at what rate, native communities re-establish following the removal of invasives. Chromolaena odorata is one of the most important invader species in the savanna biome in SouthAfrica. It reduces vegetation heterogeneity in grasslands, savannas and forests. 3. Spiders, as ecological indicators for change, were used to investigate the impact of (i) C. odorata invasions, (ii) C. odorata invasion durations, and (iii) the impact of clearing C. odorata on abundance, assemblage patterns, diversity and estimated species richness of spiders. 4. The progressive invasion of C. odorata with increasing invasion duration brings with it changes in native spider abundance, assemblage patterns, diversity and estimated species richness. Native spider assemblages do re-establish after clearing C. odorata without further management intervention. Small lingering differences are observed between the native and the cleared sites, suggesting that other features of the habitat may have been affected by the invasion and clearing. 5. Synthesis and applications . Alien clearance is an essential and invaluable management tool. There are a substantial number of programmes that aim to control alien invasive plants but very little is known about the way in which biodiversity recovers after alien plant removal. Our data show that the removal of alien invasive plants benefits biodiversity with immediate effects, highlighting that management should be carried out to control this invasive, even if the area has been invaded for a long period of time. These data are important for policy-forming and informing policy-makers that alien invasion and removal are critical for biodiversity conservation management.

South African National Survey of Arachnida (SANSA): review of current knowledge, constraints and future needs for documenting spider diversity (Arachnida: Araneae)

“…A total of 38 PAs have been sampled, with 24 represented by >50 samples (Table 2). Species lists and diversity data of several reserves have been published: Ndumo Game Reserve Wesołowska & Haddad, 2009), Tembe Elephant Park , the Mkhuze Game Reserve and Phinda Private Game Reserve (Lovell et al, 2007), Hluhluwe/iMfolozi Park (Mgobozi et al, 2008;Ngome State Forest (Van der Merwe, 1994;Van der Merwe et al, 1996;Dippenaar-Schoeman et al, 2006b), and the iSimangaliso Wetland Park (Combrink, 2007;Combrink & Kyle, 2006).…”

“…are near endemic (Foord et al, 2011b). The Savanna Biome has been the most intensively studied in the Limpopo Province (Whitmore et al, 2001(Whitmore et al, , 2002aFoord et al, 2002Foord et al, , 2008Foord et al, , 2013Foord & Dippenaar-Schoeman, 2003;Dippenaar-Schoeman & Leroy, 2003;Modiba et al, 2005;Dippenaar et al, 2008;Muelelwa et al, 2010), but several studies have been published from KwaZulu-Natal (Lawrence et al, 1980;Haddad et al, , 2010Mgobozi et al, 2008), Mpumalanga (DippenaarSchoeman & Leroy, 2003;Robertson et al, 2011) and parts of Gauteng (Dippenaar-Schoeman et al, 1989). The potential of spiders to serve as diversity surrogates was investigated by Foord et al (2013), and spiders have also been included in several ecological studies on arthropods in the biome (Nicolai, 1989;Rivers-Moore & Samways, 1996;Blaum et al, 2009;Lovell et al, 2009Lovell et al, , 2010Jonnson et al, 2010).…”

“…Also in KwaZulu-Natal, Mgobozi et al (2008) sampled spiders with pitfall traps and vegetation beating in the Hluhluwe-iMfolozi Park and found significant impacts of an invasive shrub (Chromolaena odorata) on spider assemblages, richness and diversity in a South African savanna. Chromolaena odorata is a non-indigenous perennial shrub that radically alters native vegetation structure and diversity.…”

Community level impacts of Microstegium vimineum on arthropod community structure and foodweb dynamics in a temperate deciduous forest.

“…For example, Heleno et al (2008) found a negative relationship between percent invasive plants and total species richness of both plants and insects on Sao Miguel island, part of the Azores archipelago. A number of other studies have also demonstrated a decrease in insect total abundance, species richness and diversity, and trophic and guild structure, particularly for herbivorous insects, in relationship to invasion by non-native plants (Mgobozi et al, 2008;Wu et al, 2009;Yoshioka et al, 2010;Simao et al, 2010).…”

“…The integration of both abiotic and biotic changes in the system via behavioral adaptations to vegetative structure and predation on lower trophic levels makes spiders useful as ecological indicators , DeVore 2011, Foelix 2011. Indeed, changes in spider communities often indicate greater changes in the ecosystem that supports these predators (Mgobozi et al 2008), so understanding the cascading effects of invasive plants on this trophic group becomes very important for ecologists and conservation biologists.…”