Functional space and the population dynamics of birds in agro-ecosystems

https://doi.org/10.1016/j.agee.2012.11.001Get rights and content

Abstract

Managing resource availability in landscapes is a key focus of biodiversity conservation action. Continued biodiversity losses suggest that current actions are inadequate, with better targeting required to ensure resource provision offsets resource deficits. This study uses the concept of functional cover types to establish links between land-use, resource availability and population dynamics. Using UK farmland birds as a model system, the links between local population dynamics and functional space (FS) composition, and the role of landscape context in modifying these relationships, are explored. The population trends of all 19 species considered were more positive or less negative in squares with greater areas of one or more FS components. Counter-intuitively, negative relationships between population trends and FS were also common. Conspecific abundance in the surrounding landscape was also identified as being an important driver of population dynamics, both directly and through its influence on the relationship with each FS component. Targeted conservation management is needed to address the very context-specific nature of local population change.

Highlights

► Functional space availability influences population dynamics of UK farmland birds. ► The strength and direction of these relationships change with landscape context. ► Conservation management must be better targeted to address context-specificity.

Introduction

Despite increases in the scale and intensity of policy and management responses designed to halt it, the rate of biodiversity loss is not slowing (Butchart et al., 2010). This suggests that the nature, structure and scale of these mitigation measures are insufficient to counteract existing drivers of decline and are, therefore, unlikely to offset the detrimental effects of either further increases in existing pressures or the emergence of novel drivers. The governing body of the Convention on Biological Diversity (CBD) met in Japan in October 2010 to adopt a revised and updated Strategic Plan (Gordon et al., 2010). Successfully meeting the post-2010 biodiversity targets set will require a more complete understanding of the mechanistic links between drivers of biodiversity decline and population dynamics so that mitigation measures can be targeted more effectively. A major challenge for the research community is to develop the approaches and tools to support these activities.

In Europe, agriculture of one form or another occupies approximately 50% of the land surface. As a consequence, European biodiversity conservation measures are founded on policy frameworks designed to deliver environmentally beneficial land management back into agricultural systems alongside production management. This integration of production and conservation management has been termed wildlife-friendly farming (Green et al., 2005) and is perhaps best evidenced by recent reforms to the Common Agricultural Policy (CAP). The CAP is widely accepted as the main driver of agricultural changes that have resulted in biodiversity losses across Europe but is now also the main policy tool for addressing these losses through the funding of agri-environment schemes (AES). However, as with global trends, biodiversity losses in Europe continue whilst pressures on biodiversity are increasing (Butchart et al., 2010, Butler et al., 2010, Gregory et al., 2009). At the Environment Council meeting in March 2010, Ministers agreed to develop a longer-term vision for biodiversity up to 2050, and stressed the need for integration with other EU policies and strategies. Nowhere is the need to develop post-2010 conservation strategies which reflect an acknowledgement of the current failure to appropriately target conservation management more pressing than in EU agricultural policy and practice; continued biodiversity losses across Europe provide further evidence that, despite significant investment from the public purse, many AES are not delivering on biodiversity objectives (Butler et al., 2007, Kleijn et al., 2011).

To date, studies linking land-use and population dynamics have tended to focus on structural cover types, exploring the relationship between species’ occurrence or abundance and particular land-uses or habitats (Rushton et al., 2004). However, such habitat association models (HAMs) are normally assumed to sacrifice generality for precision and reality and, by treating habitats independently, they can become context-specific and over-parameterised (Graf et al., 2006). Thus HAMs can be relatively successful at predicting species’ occurrence or population dynamics from habitat characteristics when applied within the region from which the data used to parameterise them were collected but are much less successful when used to make predictions outside the area or habitat conditions for which the model has been calibrated (Schaub et al., 2011, Whittingham et al., 2007). This limits their application because they cannot be used to predict population responses to land-use change if the resultant land-use does not appear in contemporary landscapes. Thus, at a time when factors such as climate change, agricultural policy reform and the introduction of genetically-modified and bio-energy crops are all predicted to have substantial impacts on land-use patterns at local, national and global scales (Rounsevell et al., 2006, Tilman et al., 2001), new approaches to link land-use to population dynamics are required.

Ultimately, species’ habitat associations are dictated by the quantity and quality of the resources they provide, rather than the habitat per se (Boyce and McDonald, 1999), although factors such as intra- and inter-specific competition or perceived and actual predation risks in specific habitats are also important (Brown and Kotler, 2004, Butler et al., 2005, Oliver et al., 2009). As a consequence, it has recently been proposed that, instead of using structural cover types, land use – population dynamics relationships might be better examined in the context of functional cover types, such as foraging or breeding habitat, identified on the basis of resource dependencies of species or species groups (Fahrig et al., 2011). The quantity, in terms of area, and quality, in terms of resource provision, of each functional cover type in a landscape effectively delimits the functional space (FS) available to a species. FS based models are likely to have three key advantages over structural cover based HAMs. Firstly, they provide a more mechanistic link between land use and population dynamics, whereby population change can be explained by changes in the availability of specific functional cover types. Secondly, by limiting the resolution of habitat re-categorisation to these principal functional cover types, the likelihood of over-parameterisation and context-specificity is greatly reduced (Graf et al., 2006). Thirdly, novel land uses can be readily incorporated into this framework, simply by quantifying their contribution to FS on the basis of resource provision.

Here the concept of FS is developed to examine whether it can be used to link land-use and population dynamics. Using UK farmland birds as a model system, structural land-covers (i.e. agricultural and semi-natural habitats) were re-classified into functional cover types according to the resource requirements of each species. A simple definition of a species’ requirements, characterised by its diet, foraging habitat and nest site was adopted because previous research has shown that changes in the quantity or quality of these key resources can be linked to national population dynamics (Butler et al., 2007, Butler et al., 2009, Butler et al., 2010). It was predicted that local population trends would be positively associated with FS availability because resource availability should affect local demography. In wide-ranging organisms such as birds, landscape-scale population processes may also influence local population trends and alter the relationships with FS through, for example, source–sink dynamics (Pulliam, 1988) so potential interactions between local and landscape-scale dynamics were also assessed.

Section snippets

Methods

Our analyses focus on the 19 species included in the UK Farmland Bird Index (FBI) (Table 1) and were based on data collected from 601 1 km squares covered by both the Breeding Bird Survey (BBS) and Winter Farmland Bird Survey (WFBS). BBS has been the national monitoring scheme for breeding bird populations in the UK since 1994 (Risely et al., 2008) whilst WFBS documented the abundance of farmland birds in the UK in the winters of 1999/2000, 2000/2001 and 2002/2003 (Gillings et al., 2008). During

FS availability

Of the 601 squares covered by both BBS and WFBS, only six did not contain any FS for a species which was recorded in it three or more times between 1994 and 2007 (Table 1). As expected, given their mutual exclusion, correlations between the available area of high and low quality space of each functional cover type for a given species were predominantly negative (one sample t-test of correlation coefficients: BHQ:BLQ t = −6.2, P < 0.001; SHQ:SLQ t = −4.8, P < 0.001; WHQ:WLQ t = −2.8, P < 0.02) whilst

Discussion

These analyses show that it is possible to describe local (1 km square) population trends for the 19 species included in the UK FBI in relation to the extent of relatively coarsely defined functional cover types and conspecific abundance in the surrounding landscape. All species showed improving population trends as the extent of one or more FS components increased but, counter-intuitively, negative impacts were also detected. Conspecific abundance in the surrounding landscape also had a strong

Acknowledgements

The authors thank J. Vickery, G. Siriwardena, S. Gillings and J. Gill for valuable discussions and D. Childs for advice on package MCMCglmm. The BBS is organized by the British Trust for Ornithology (BTO) and is jointly funded by the BTO, the Joint Nature Conservation Committee (JNCC, on behalf of the Countryside Council for Wales, English Nature, Scottish Natural Heritage and the Department of the Environment for Northern Ireland) and the Royal Society for the Protection for Birds. The WFBS

References (51)

  • K. Bartoń

    MuMIn: Multi-Model Inference Package, Version 1. 7. 7

    (2009)
  • J.S. Brown et al.

    Hazardous duty pay and the foraging cost of predation

    Ecol. Lett.

    (2004)
  • K.P. Burnham et al.

    Model Selection and Multimodel Inference: A Practical Information – Theoretic Approach

    (2002)
  • S.H.M. Butchart et al.

    Global biodiversity: indicators of recent declines

    Science

    (2010)
  • S.J. Butler et al.

    Stubble height affects the use of stubble fields by farmland birds

    J. Appl. Ecol.

    (2005)
  • S.J. Butler et al.

    A cross-taxonomic index for quantifying the health of farmland biodiversity

    J. Appl. Ecol.

    (2009)
  • S.J. Butler et al.

    Farmland biodiversity and the footprint of agriculture

    Science

    (2007)
  • D.E. Chamberlain et al.

    Changes in the abundance of farmland birds in relation to the timing of agricultural intensification in England and Wales

    J. Appl. Ecol.

    (2000)
  • C.M. Davey et al.

    Assessing the impact of entry level Stewardship on lowland farmland birds in England

    Ibis

    (2010)
  • J. Ekroos et al.

    Landscape context affects the relationship between local and landscape species richness of butterflies in semi-natural habitats

    Ecography

    (2011)
  • L. Fahrig et al.

    Functional landscape heterogeneity and animal biodiversity in agricultural landscapes

    Ecol. Lett.

    (2011)
  • R.H. Field et al.

    Habitat use by breeding tree sparrows Passer montanus

    Ibis

    (2004)
  • R. Freckleton

    Dealing with collinearity in behavioural and ecological data: model averaging and the problems of measurement error

    Behav. Ecol. Sociobiol.

    (2011)
  • S. Gillings et al.

    Winter availability of cereal stubbles attracts declining farmland birds and positively influences breeding population trends

    Proc. R. Soc. B: Biol. Sci.

    (2005)
  • S. Gillings et al.

    Distribution and abundance of birds and their habitats within the lowland farmland of Britain in winter

    Bird Study

    (2008)
  • Cited by (21)

    • The adequacy of alfalfa crops as an agri-environmental scheme: A review of agronomic benefits and effects on biodiversity

      2022, Journal for Nature Conservation
      Citation Excerpt :

      These differences may be related to the different resources sought by birds within alfalfas, and the mechanism by which they are influenced by those resources. The occupation of a particular habitat by a particular species does not usually depend on the habitat per se, but may be mainly related to the amount and quality of resources it harbours (Butler & Norris, 2013; Ponce et al., 2014). The combination of alfalfa with other agricultural habitats in the landscape may contribute to enhance resource availability for birds through their influence on plants or insects (Fig. 2).

    • Time, geography and weather provide insights into the ecological strategy of a migrant species

      2019, Science of the Total Environment
      Citation Excerpt :

      This phenomenon can be partially explained by the fact that male and female quail were generally ringed in April and May, respectively, so it is to be expected that more ringed males would be encountered in May than ringed females, and more ringed females in June than in May. Spatio-temporal sex segregation allows quail to disperse and aggregate, and to link localities (latitude and altitude) with breeding attempts (herbaceous ripening) (Butler and Norris 2013; Visser and Sanz 2009). This is probably a strategy to avoid predation (through dispersion) on the one hand and to facilitate successful breeding (through aggregation) on the other.

    View all citing articles on Scopus
    View full text