Niche models and translocation experiments: do they predict different responses to climate change?

A metapopulation model had three stages: seeds, rosettes, and juveniles. The model included vital rates of Carlina vulgaris individuals when grown in their home territory. To incorporate responses of life history traits to climate change, these rates were altered to match those of C. vulgaris when translocated

by Rebecca Swab

Translocation experiments are often used to determine how plants respond to climate change. Individuals from various parts of a species’ range are locally adapted. Thus, even when experiencing climates within their home range, individuals can exhibit differences in factors such as growth rates or seed production. Species distribution models are also used to predict responses of plants to climate change.  However, in this case the entire range of the species is used to predict changes in habitat suitability. Each of these methods focuses on different aspects of species responses to climate change: translocation experiments evaluate changes in life history traits whereas species distribution models focus on environmental suitability.  Given that these are both important aspects of species’ responses to climate change, can the two methods be used together to improve predictions?

To explore this, we generated a metapopulation model incorporating the vital rates of Carlina vulgaris individuals grown in their home territory. Changing habitat suitability, as predicted by a species distribution model, affected the carrying capacity of populations within the model. 

Predicted habitat suitability for Carlina vulgaris with (a) current climate (b) predicted climate in 2050 under scenario A1B (c) predicted climate in 2080 under scenario A1B. Greener colors indicate increasing suitability of habitat. Plus symbols indicate translocation sites.

Then, we varied the demographic rates based on vital rates of C. vulgaris individuals when grown away from home. Thus, we were able to compare predictions of the species response to altered habitat suitability with potential changes in life history traits. We also looked at how the two aspects of species responses to climate change might interact.

Did changes in vital rates reverse the impact of changing habitat suitability? In some cases, yes. Some populations with projected declines in carrying capacity actually experienced increases in expected minimum abundances due to increased fecundity, and vice versa.

Percentage of scenarios with increases (+) or decreases (-) in EMA for Carlina vulgaris metapopulation model results given increases (+) or decreases (-) in fecundity and habitat suitability (HS). Increases or decreases in EMA are as compared with the EMA for a similar scenario, but with stable habitat and home fecundity values. 

There were even instances where both habitat suitability and fecundity increased, but minimum abundances still declined. This is an example of how the complexities of species responses to climate change makes reactions difficult to predict.  For one, at particular locations, populations could experience increases as individuals respond to local climate change even if the species as a whole is declining.  Alternatively, and of a bit more concern for conservation purposes, species with projected increases in habitat suitability under climate change could experience declines in abundances and even extirpations across the range as individuals experience changes in vital rates.    

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