Habitat heterogeneity must play a significant role in determining the occurrence, amount and persistence of biodiversity. Well, at least this is what our gut feeling is telling us. Reality, however, seems to be that we now very little about the effects of heterogeneity in different environments and next to nothing generalizable over different environments and scales. Indeed, as Tews et al. (2004) pointed out in their highly sited review, there seems to be a positive correlation between habitat heterogeneity and animal species diversity, but it’s all very species and scale dependent. Furthermore, studies have tended to be very biased towards certain species groups and environments.

Agricultural landscapes are probably one of the more studied environments. In this week’s journal club we read through Fahrig et al. (2010): “Functional landscape heterogeneity and animal biodiversity in agricultural landscapes”. Many of us had hoped for a review-type paper pulling together information on empirical work that has been carried out in agricultural landscapes. Equally, after reading the paper many of us felt a little baffled by the scope of the paper as it turned out not to be a review, but rather a “Idea and Perspective” type of contribution. Authors’ describe their objectives threefold (shortened from the original):

1. to develop a conceptual framework for the study on landscape heterogeneity in the context of agricultural landscapes
2. identifying three important unanswered questions about the relationship between landscape heterogeneity and biodiversity in agricultural landscapes
3. to suggest a general methodological approach for studies to address aforementioned questions

Our greatest complaint about the paper was a general vagueness we felt it has. This may be partly unjustified as it is a perspective paper, but still we would have appreciated more literature (and especially empirical studies) sited, and clearer connection to policy making and implementation. Neither the conceptual framework nor the proposed study questions struck us particularly novel. Dividing heterogeneity into two main components – compositional and configurational – is useful, but we felt that this is generally the way heterogeneity has been treated previously as well. The division between structural and functional heterogeneity reminded us very much about the treatment of connectivity popular especially in the context of landscape ecology.

Far more interesting aspect of the paper is the discussion on what sort of effects does heterogeneity have in different kinds of landscapes and where should it be promoted from biodiversity conservation point of view. These questions are formulated as the three research questions the authors are proposing. Does increasing heterogeneity (or the different components of heterogeneity) increase biodiversity both in more-natural environments as well as in production environments? To put it differently, is increasing heterogeneity more beneficial in more-natural or production kinds of environments? Also, what levels of heterogeneity are desirable? The latter question the authors address by stating that often a times intermediate levels of heterogeneity seem to result in the most biodiverse environments. This observation is similar to that of classical Intermediate Disturbance Hypothesis in ecology.

On the policy side Fahrig et al. emphasize that

“agri-environment policy should aim to enhance biodiversity to the extent possible while still providing agricultural products for human consumption”

and that

“Policies aimed at increasing the heterogeneity […] thus reducing agricultural production, will frequently be considered unacceptable by farmers”

Authors are thus emphasizing the main function of agriculture: food production. Given the heavy subsidization of agriculture especially in the EU and the US, it seems the there would be more space for agri-environment schemes and economical instruments. Farmers pay check does not come only from selling revenues, but to a great extent from different subsidies. Therefore decreased production might be acceptable if the loss is compensated in some other manner.

In conlusion, the paper was an interesting read, but an unnecessary lengthy one and from a bit different perspective that at least some of us had hoped for. Obviously more research is needed before we can really say something generalizable on the effect of habitat heterogeneity on the amount in biodiversity, in agricultural landscapes or elsewhere.

Full reference: Fahrig L, Baudry J, Brotons L, et al. 2010: Functional landscape heterogeneity and animal biodiversity in agricultural landscapes. Ecology letters. Link to paper

Extra reference: Tews J, Brose U, Grimm V, et al 2004: Animal species diversity driven by habitat heterogeneity/diversity: the importance of keystone structures. Journal of Biogeography. 2004;31:79-92.