Historical distribution and regional dynamics of twoBrassicaspecies

Abstract

Plants often show a patchy distribution. This can be related to the discontinuous distribution of environmental variables that define suitable habitat. Metapopulation theory suggests that additional patchiness may be caused by the dynamics of local extinctions and recolonisations. However, the contribution of these two mechanisms to explaining the observed patterns, and thus the applicability of metapopulation theory to plants remains controversial partly because population turnover may occur at long time-scales not usually covered by ecological studies. We analyzed the role of environmental variation and population turnover in determining the distribution of two Brassica species, an annual and a perennial, along 44 km of coastline in Dorset, UK. Mapped occurrence and abundance of both species in recent years was compared with distributions from a 70 yr-old dataset and a survey of present-day environmental parameters. Abiotic and vegetation parameters were correlated with the occurrence of both species in binary logistic regression models and explained spatial auto-correlation in the Brassica distributions. These regression models suggest that neither species is occupying all potential habitat in the region studied. The relationship between historical and present distributions differed between the species. While an historical signal was very weak in the annual B. nigra, it had a large influence in predicting the present distribution of the perennial B. oleracea. This suggests local extinction and colonisation events for B. nigra over the 70 yr period, but not for B. oleracea which showed little evidence of population turnover. Our results demonstrate that the consideration of large time-scales can reveal patterns of regional dynamics. We conclude that metapopulation dynamics might be possible for our annual but can be ruled out for our perennial study species over the past 70 yr. We argue that beyond this time-scale possible metapopulation dynamics may be overridden by faster processes of environmental change.

Smelling the Wood from the Trees: Non-Linear Parasitoid Responses to Volatile Attractants Produced by Wild and Cultivated Cabbage

“…These wild cabbage populations generally are regarded as the native wild form of cultivated cabbage (Wichmann et al 2008). The three wild populations were located at sites known as ‘Old Harry’ (‘OH’, 50°38′N, 1°55′E), ‘Kimmeridge’ (‘KIM’, 50°35′N, 2°03′E), and ‘Winspit’ (‘WIN’, 50°36′N, 2°07′E).…”

Bottom‐up effects of glucosinolate variation on aphid colony dynamics in wild cabbage populations

“…In addition, recent studies have shown that the upregulation of genes in the aliphatic biosynthetic pathway causes a reciprocal repression in the indole pathway, and vice versa (Reviewed in Gigolashvili et al, 2009). Natural populations of B. oleracea tend to be very long-lived (Wichmann et al, 2008) and show inter-and intra-population variation in aliphatic glucosinolates (Mithen et al, 1995b;Moyes et al, 2000), providing sufficient variation in this aspect of antiherbivore chemistry to allow powerful experiments and surveys. Furthermore, Newton et al (2009) found that variation in herbivore attack on B. oleracea plants and populations were linked strongly to presence/absence patterns of aliphatic glucosinolates.…”

Differentiation and adaptation in Brassica nigra populations: interactions with related herbivores

“…Brassica nigra (L.) W.D.J Koch is an annual, predominantly outcrossing species that occurs in disturbed coastal and river valley habitats, such as coastal wetlands, cliffs and marshes, river banks, arable fields and ditch edges (Klotz et al 2002;Watson-Jones et al 2006, Wichmann et al 2008. It has been introduced to central and western Europe as a crop plant for oil and mustard production, but information on its origin and date of introduction varies widely in the literature; some floras even consider the species to be native (Klotz et al 2002;Preston et al 2002).…”