Biotic homogenization and changes in species diversity across human-modified ecosystems

Abstract

Changing land use and the spread of 'winning' native or exotic plants are expected to lead to biotic homogenization (BH), in which previously distinct plant communities become progressively more similar. In parallel, many ecosystems have recently seen increases in local species (a-) diversity, yet g-diversity has continued to decline at larger scales. Using national ecological surveillance data for Great Britain, we quantify relationships between change in a-diversity and between-habitat homogenizations at two levels of organization: species composition and plant functional traits. Across Britain both increases and decreases in a-diversity were observed in small random sampling plots (10-200 m 2 ) located within a national random sample of 1 km square regions. As a-diversity declined (spatially in 1978 or temporally between 1978 and 1998), plant communities became functionally more similar, but species-compositional similarity declined. Thus, different communities converged on a narrower range of winning trait syndromes, but species identities remained historically contingent, differentiating a mosaic of residual species-poor habitat patches within each 1 km square. The reverse trends in b-diversity occurred where a-diversity increased. When impacted by the same type and intensity of environmental change, directions of change in a-diversity are likely to depend upon differences in starting productivity and disturbance. This is one reason why local diversity change and BH across habitats are not likely to be consistently coupled.

The impact of agricultural intensification and land-use change on the European arable flora

“…However, of potentially greater concern for arable plant biodiversity at the national and continental scale is the more general trend towards the intensification of agriculture with the consequent biotic homogenization of the landscape [39,40]. The results presented in this paper support the conclusions of previous studies that eutrophication, either through atmospheric nitrogen deposition or fertilizers, is one of the major drivers of decreasing habitat heterogeneity and species loss [41][42][43], and that declining species are spread disproportionately across plant families, potentially contributing to the phylogenetic shift in the European flora [44].…”

Distribution of crop wild relatives of conservation priority in the UK landscape

“…These twin pressures non-randomly filter species based on their traits. Thus 'winners' tend to be tall woody species or fast growing forbs and grasses while 'losers' are more likely to be shorter, slower-growing forbs (Smart et al, 2006b;Tamis et al, 2005;Walker et al, 2009). Where linear features are subject to intermittent or frequent removal of biomass and lack of direct fertilizer application, conditions mimic lower intensity agriculture.…”

Coralligenous habitat: patterns of vertical distribution of macroalgal assemblages

“…In fact, beta diversity, defined as the change of species composition and abundance along environmental gradients (between-habitat diversity), is an important aspect for ecological studies and contributes highly to the total diversity of marine systems (Legendre et al, 2005;Gray, 1997Gray, , 2000. It is known that changes in alphadiversity can be completely uncoupled from betweenhabitat homogenization (Olden and Poff, 2003); thus, the replacement of locally distinctive assemblages with widespread species caused by disturbance could lead to a decrease in beta-diversity while alpha-diversity could remain unchanged (Smart at al., 2006). This correlative study does not reveal any causeeffect relationships; however, patterns detected in the present study are in agreement with the results of manipulative studies (Balata et al, 2007a(Balata et al, , 2007b), suggesting that different environmental conditions, mostly related to different levels of sedimentation and pollution, can be the cause of the observed patterns.…”