Demographic variation between populations of Caladenia orientalis - a fire-managed threatened orchid

Abstract

Caladenia orientalis (G.W.Carr) Hopper & A.P.Br. is a critically endangered orchid. The largest known populations are confined to fire-managed coastal heathland in southern Victoria. Trends in population dynamics at two closely occurring sites were evaluated against time since fire and rainfall, between 2000 and 2008, to provide ecological and biological information relevant to population management. At both sites, decreased plant size was inversely correlated with time since fire and the number of non-reproductive plants was positively correlated with time since fire. Rates of flowering were inversely correlated with time since fire at only one site (Population 2). The vegetation at this site rapidly accumulated after fire, whereas recovery was relatively slow at the other site. Rainfall was not correlated with rates of flowering or leaf width at either of the study sites, although there was a weak inverse relationship between rainfall and the number of non-reproductive plants at one site (Population 1). Rates of pollen transport and fruit set were within reported ranges for deceptive species. Fruiting plants were significantly smaller in the following year, whereas non-reproductive plants remained the same size. The results suggest that there may be costs associated with reproductive effort, and that hand-pollinating plants to boost seed production may lead to decreased plant size in the following year. Annual variation in rates of flowering may be influenced by previous reproductive effort. However, long-term population trends are better explained by competition from dominant shrubs, which become increasingly abundant with a lack of fire. Future management prescriptions should include site-specific fire regimes to maintain an open heathland.

Effects of fire on pollinators and pollination

“…Interspecific differences in the onset and cessation of flowering can correspond approximately to growth form. Trees take longer than shrubs, which take longer than herbs, to reach reproductive maturity following fire (Burrows, Wardell‐Johnson & Ward ), and taller‐stature plants can inhibit flowering of lower‐stature plants through competition for light and other resources as their canopies recover from fire (Coates & Duncan ; Keeley et al . ).…”

“…Interspecific differences in the onset and cessation of flowering can correspond approximately to growth form. Trees take longer than shrubs, which take longer than herbs, to reach reproductive maturity following fire (Burrows, Wardell-Johnson & Ward 2008), and taller-stature plants can inhibit flowering of lower-stature plants through competition for light and other resources as their canopies recover from fire (Coates & Duncan 2009;Keeley et al 2011). For taller-stature plants, flowering capacity may cease with adult senescence, bud bank attrition or due to a lack of environmental cues associated with fire (Enright et al 2011;Lamont & Downes 2011).…”

Population viability analysis of Critically Endangered white-rumped vultures Gyps bengalensis

“…Crouse et al 1987, Tremblay 1997, Beissinger & Westphal 1998. Because of its useful functions, there have been numerous case studies using PVA to address various aspects of rare and endangered species management, including estimating extinction probability (Dennis et al 1991, Morris & Doak 2002, Masatomi et al 2007, testing the efficacy of recovery and reintroduction (Dennis et al 1991, Kohlmann et al 2005, Zeoli et al 2008, Schaub et al 2009), assessing habitat requirements (Perkins et al 2008, Coates & Duncan 2009, and analyzing the costeffectiveness of conservation programs (Marshall et al 2000, Bode & Brennan 2011.…”

Ecological interactions of the sexually deceptive orchid Orchis galilaea

“…In each orchid population, 10 plants per patch were randomly selected and marked with wooden tags (Coates and Duncan 2009). When there were fewer than ten flowering individuals in a patch, all individuals were marked (Jacquemyn et al 2002b).…”

“…A patch was defined as a continuous aggregation of at least two individuals separated by at least two meters from neighboring patches (Dauber et al 2010;Tscheulin and Petanidou 2010). Based on the 200 m dispersal range of L. marginatum (S. Roberts, personal communication, 2010), selected populations of O. galilaea were at least 500 m apart (Coates and Duncan 2009;Dauber et al 2010). Within each population, a maximum of four distinct patches of O. galilaea plants were selected for measuring reproductive success (Tscheulin and Petanidou 2010).…”