It’s the city life for me… or maybe not.

Michael Fitch wrote this post as part of Dr. Stacy Krueger-Hadfield’s Evolution course at the University of Alabama at Birmingham. He completed a B.S. in Biology from the UAB and is currently considering entering the Master’s program.  Current interests… all over the place.

As urban sprawl expands and consumes the last wild places, do we pause to think about the consequences? 

Take apex predators, as an example. How does urbanization affect animals that likely range over large areas?

Tumbo et al. (2019) seek to uncover how the process of urbanization is affecting gene flow and genetic diversity in the puma (Puma concolor; Figure 1).  Using a combined analysis of terrain features and genetic diversity in the southern Rocky Mountains, they were able to provide some insight on these puma populations. 

Figure 1. Puma concolor

For these broad ranging, yet shy creatures, territories can easily be fragmented.  By collecting GIS data for the Front Range and the Western Slope of Colorado, Tumbo et al. (2019) used vegetation density, tree canopy, rivers, roads, and geographic distance between individual animals. They combined these data with ddRADseq genotyping by sequencing to paint a picture of how these animals are being affected by the terrain in more urban vs. rural environments (Table 1).

Table 1. Study areas (km2), number of individuals genotyped (Ngen), and population genomic parameter estimates from the Western Slope and Front Range of Colorado.
Note: Population genomic measures are observed heterozygosity (Hobs), expected heterozygosity (Hexp), nucleotide diversity (π), allelic richness (Ar), inbreeding coefficient (FIS), genetic differentiation
among populations (pairwise FST), mean genetic distance among individuals corrected for geographic distance (DPS and r per km) with standard errors (SE), and effective population size (Ne) with 95%
confidence intervals (CI) based on parametric bootstrapping.

Tree canopy was critical for dispersal in rural areas, while low shrub and grass cover was preferred in urban environments.  While dispersal with low shrub and grass cover was possible, it does not appear to be as effective as that provided in the rural areas.  

When comparing the Front Range to the Western Slope of the southern Rocky Mountains, there wasn’t much difference in terms of genetic diversity.  Table 1 shows the effects on population size and genetic distance in these populations. They are beginning to show some signatures at the urbanized Front Range. This appears to be caused by the inability of these cats to move as freely though these urban areas, thereby restricting their ability to find mates.  This could (and probably will) lead to inbreeding depression and a loss of genetic diversity in urban populations.  Habitat fragmentation such as that seen in urban areas has been linked to an increased risk of extinction, with range size being cited as the most important risk factor (Crookset al. 2017).

 Understanding how these populations are affected by urbanization is going to be a key element in preserving these majestic animals, and the ecosystems in which they (and we) live.  Providing safe passages for these animals to disperse in a more natural fashion could be a future goal in urban development.  Like the leopards that wander the streets of Mumbai, this could be extremely beneficial to the people of the city by helping to balance the local ecosystem and prevent the spread of disease (Braczkowski et al. 2018).  

References

Braczkowski AR, O’Bryan CJ, Stringer MJ, Watson JEM, Possingham HP, Beyer HL (2018)  Leopards provide public health benefits in Mumbai, India. Frontiers in the Ecology and Environment 16: 176-182.

Crooks KR, Burdett CL, Theobald DM, King SRB, Di Marco M, Rondinini C, Boitani L. (2017) Habitat fragmentation and extinction risk. Proceedings of the National Academy of Sciences 114 (29) 7635-7640

Trumbo, DR, Salerno, PE, Logan, KA, et al. (2019) Urbanization impacts apex predator gene flow but not genetic diversity across an urban‐rural divide. Molecular Ecology 28: 4926-4940

About Stacy Krueger-Hadfield

I am a marine evolutionary ecologist interested in the impacts of seascapes and complex life cycles on marine population dynamics. I use natural history, manipulative field experiments and population genetic and genomic approaches with algal and invertebrate models in temperate rocky shores,estuaries and the open ocean.
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