Where in the landscape are the refugia?

Locating areas where species will likely persist in future climate changes has recently become a conservation priority. How do we find these areas? A good first step is to look for places that species persisted through past climate changes (often termed ‘refugia’).

Clearly, the assumption that past refugia predict where future refugia will be depends on the nature of climate change. It is more likely if future climate change mimics past climate change, but may also be the case if past and future climates are different. Why? One reason is that local climates in refugia tend to be unique to their surroundings–buffering climate extremes for example. Or maybe they are mesic habitats in an arid landscape.

Populations of E. baxteri and closely related species on rocky, western slopes (‘West’ and ‘Endemics’) less diverse than eastern populations

In either case, we can better judge whether a past refugia will be a future one if we understand how local climates and landscape features are related to species persistence. We have a new paper out in the Journal of Biogeography that is an attempt at doing this. We looked within a regional refugium to find local conditions that match patterns of genetic diversity across the landscape.

We found populations of eucalypts on side slopes and valleys with deep, moist soils and protection from strong westerly winds were more genetically diverse than populations on exposed rocky slopes.

The Serra Range in the Grampians National Park in Victoria, Australia. The Grampians ranges are a cuesta formation with western dip slopes (left side of photo) and steep eastern slopes. Species may have persisted in the mesic east-facing slopes and disappeared from rocky west-facing slopes when climates were colder and drier

It seems fairly obvious that species would persist in nicer habitats, but this story was only revealed with genetics (not obvious from morphology or species composition). These findings help strengthen the case that mesic local climates in semi-arid Australia may serve as refugia.

The second part of this paper is about gene flow between species.. A complicated story for another day..

Linking functional traits and species distributions

We have a new paper out in Ecography. The aim was to link functional traits to environmental gradients. There are existing methods that do this, but they generally involve multiple steps. We created a hierarchical model that effectively joins a species distribution model with species trait values in one step. We were quite happy with the model because it worked well-better than we anticipated for rare species-and, importantly, produced sensible and interpretable results. Here is one example.

Specific leaf area (SLA) represents a tissue allocation strategy of either growing quickly or growing slowly with more tissue devoted to protection or conserving resources. SLA modifies species responses to rock cover. So, species with low SLA (thick, tough leaves) tend to increase in occurrence on increasingly rocky areas. Species with higher SLA (flimsy leaves) tend to be found on deeper, less rocky soil (see Figure).

The y-axis label looks complicated, but it’s simply the expected change in probability of species occurrence for a given change in surface rock cover. (technically, this is a partial response)..

Some key aspects of the model are:

1- species trait values actually modify species responses to environmental gradients. This may be useful for improving species distribution models when trait values are known.

2- rare species borrowed strength from common species. Species that are uncommon or have restricted distributions are usually quite difficult or impossible to model. I think this type of multi-species modelling shows real promise in this area.

Welcome

I’ve finally been coerced into the online world beyond email. This is my attempt at sharing some of my research and hopefully connecting with other people with similar interests. And, if the time I spent picking out the theme for my blog is any indication, this will also be a great procrastination tool.