Not all connectivity is created equal. Identifying areas with high functional connectivity – in other words, how organisms respond to the structural elements in the landscape – is essential for prioritizing conservation strategies that maintain connectivity benefits and allow metapopulations to persist. The ongoing pressure of urbanization, habitat loss due to land-use change, and the effects of climate change can increase the distance between habitat patches, impeding species movement. Habitat patches that are small and isolated make it more likely for populations within them to decline, leading to a loss in biodiversity.
Hordley, L.A., Powney, G.D., Brereton, T., Gillings, S., Petchey, O.L., Roy, D.B., Tobias, J.A., Williams, J. and Oliver, T.H. 2022. Developing a national indicator of functional connectivity. Ecological Indicators 136: 108610.
The movement of species is not only dependent on land-cover but other factors, such as species interaction and dispersal ability. Metapopulations with habitat patches in close proximity may experience similar conditions, which could result in a corresponding increase or decrease in population size. The measure of similarity in population dynamics between different sites over time is known as population synchrony. The more isolated and fragmented the habitat, the less likely metapopulations will experience similar population fluctuations, and vice versa.
Synchronized population dynamics may also be the response of environmental factors, such as climate. This is important since species population synchrony could be impacted by climate change. However, once climate is accounted for, it’s possible to determine population synchrony that is influenced by density-dependent factors. Doing so could allow researchers to better quantify the degree of functional connectivity in a given habitat over time.
A new study utilizes decades-long survey data of 58 bird and butterfly species from the UK Butterfly Monitoring Scheme, the Common Birds Census and the Breeding Bird Survey to determine if the trends in population synchrony could be used as an indicator of the degree of functional connectivity. To account for population synchrony due to climate, researchers measured the average temperature and rainfall for each season over each monitoring site. To estimate changes in species abundance, population trends were averaged over ten year time differences along with population changes at varying distances.
The analysis revealed how population synchrony of birds and butterflies are influenced by climatic changes, specifically temperature and rainfall. As expected, sites closer in proximity and of similar habitat types showed a higher degree of population synchrony. Synchrony in butterflies declined over time by 71% between 1985 and 2000 but increased by 64% in more recent years, while 74% of bird species showed no significant change in synchrony.
These findings demonstrate that population synchrony can be a useful indicator of tracking functional connectivity. Utilizing long-term datasets conservation managers can identify temporal population trends that could help progress towards biodiversity goals and improve reserve design.
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