Follow the Lemur: Size of a habitat fragment may have greater impact on lemur populations than its isolation

Follow the Lemur: Size of a habitat fragment may have greater impact on lemur populations than its isolation

Sometimes cute animals may not appear to be endangered and lemurs are no exception. Nearly all lemur species are at risk of extinction, primarily due to habitat loss and fragmentation – division of their habitat into smaller parcels, usually because of human activity – in Madagascar, where they live exclusively.

To better understand how forest loss and fragmentation affect lemurs, ecologists Travis Steffens and Shawn Lehman observed six lemur species living within 42 fragments of the dry deciduous forest in Ankarafantsika National Park, Madagascar, between June and November 2011. The researchers then used mathematical models to examine whether the lemurs formed metapopulations, spatially separated populations within a species, in a fragmented landscape and under different forest fragmentation conditions.

In their simulations, the researchers found that three of the lemur species did form metapopulations in forest fragments. The number of individual lemurs within each metapopulation was affected by both forest fragment size and isolation. However, fragment size appeared to have a bigger effect than isolation, with larger forest patches being associated with increased lemur occurrence.

I spoke with Travis Steffens about the implications of these findings and how they might affect lemur conservation in future, as Madagascan forests are becoming increasingly fragmented.

What drew you to studying lemurs?

TS: I have always wanted to understand how primates respond to habitat change, and Madagascar has a high degree of habitat transformation typically caused by humans. It is one of the best places to understand how habitat loss and fragmentation impact primates.

Why are lemurs at risk for extinction?

TS: Mainly due to habitat loss and habitat fragmentation. Arguably, half of lemur habitat has been lost since the 1950s. However, lemurs are also at risk of extinction from hunting and capture for the pet trade.

Was there anything surprising about your results?

TS: There were a few things that surprised me. One was that lemur species of the Microcebus genus had higher occurrence probabilities in more- versus less-isolated fragments. The other was that we found Microcebus species in some of the smallest fragments recorded, including fragments as small as 0.23 hectares.

Do the lemur metapopulations you studied function differently from an un-fragmented lemur population? If so, how?

TS: In a continuous forest lemurs would more readily interact with intergroup conspecifics [i.e., members of the same species in different groups]. However, the lemurs forming metapopulations in our study are likely more limited in their ability to move and disperse between fragments because of the hostility of the matrix. However, we still need more study to fully understand how primates move through landscapes with fragmented habitats surrounded by apparently hostile, such as grassland, matrix.

What were the limitations of your study?
TS: Studying metapopulation dynamics in fragmented habitat in primates is difficult. You need a place where there is a sufficient number of fragments, that are surrounded by clear non-habitat, in a landscape that was fragmented long enough ago that a dynamic equilibrium has begun to form, and with a sufficient number of species for comparative purposes. Fortunately our site is ideal for investigating metapopulation dynamics in lemurs because it meets each of these criteria. One specific limitation of our study was that we used visual surveys to identify the two cryptic Microcebus species. We found it hard to identify them in nearly half of our observations. To accommodate this limitation we removed ambiguous observations for our analysis of each species and ran a separate genius level analysis.

What impact might your study have on lemur conservation?

TS: We think that our study highlights the importance of habitat fragment area over isolation in maintaining stable metapopulations over time. We suggest that conservation efforts should be placed on maintaining or increasing habitat amount. However, for some species such as common brown lemurs (Eulemur fulvus) the impact of fragment isolation should be considered. Fortunately, increasing habitat amount has the secondary effect of reducing isolation in fragmented landscapes.

Reference: Steffens TS, Lehman SM (2018) Lemur species-specific metapopulation responses to habitat loss and fragmentation. PLoS ONE 13(5): e0195791. https://doi.org/10.1371/journal.pone.0195791

Image Credit: Travis S. Steffens

Author

Tessa is the Journal Media Manager at PLOS. She graduated from the University of California, Berkeley with degrees in Rhetoric and Music. She can be reached by email at tgregory@plos.org and on Twitter at @tessagregs.

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