Human impacts on ecological connectivity

Posted on June 19, 2017

Ecological connectivity – the exchange of organisms between habitat patches or subpopulations – has an influence on many key processes, including population dynamics, nutrient flux, disease transmission, species invasions, food-web interactions, genetic isolation and the maintenance of biodiversity. A recent study reviewed ways in which graph theory has been used to investigate how human activities alter ecological connectivity in aquatic systems. Graph theory can help to describe a wide variety of systems, ranging from metapopulations to social interactions. A spatial graph consists of an arrangement of ‘nodes’ (such as habitat patches or subpopulations), connected through ‘links’ (such as dispersal or migration), and provides a compact picture of the system and its dynamics.  A literature search identified 42 relevant studies, published in 2000–2014, in which graph theory was applied to marine or freshwater ecology.  Many of the studies examined the effects of habitat alteration on aquatic (mainly riverine) connectivity – for example, by simulating the removal or re-establishment of habitat nodes in a network to help prioritise sites for conservation or restoration.  Other research investigated how habitat connections are altered by interruptions, such as dams and road crossings, that reduce or remove links between nodes.  Some studies considered how connectivity can be increased by the creation of new habitats in the form of fish farms and hatcheries, and work has  been carried out to explore the ways that activities such as boating and fishing and the release of aquarium species create new network links that allow invasions of alien species.  Climate change has also been the focus of study: rising temperatures are expected to affect nodes and links by altering habitats, river flows, the sizes of populations and the activities of migrating organisms. Graphical approaches have also been used to examine the network-level implications of the loss of particularly well-connected nodes, such as stepping stone habitats and keystone species.

Reference: Saunders, M.I. et al.   2016. Human impacts on connectivity in marine and freshwater ecosystems assessed using graph theory: a review. Marine and Freshwater Research 67, 277–290.