Steppe Marmot: An ecosystem engineer rodent in arid steppes

Our new paper about the habitat transformation activity of a steppic ecosystem engineer rodent species has recently been published in the Journal of Arid Environments.

The citation of the paper is

Valkó, O., Tölgyesi, C., Kelemen, A., Bátori, Z., Gallé, R., Rádai, Z., Bragina, T.M., Bragin, Y. A., Deák, B. (2020): Steppe Marmot (Marmota bobak) as ecosystem engineer in arid steppes. Journal of Arid Environments doi: 10.1016/j.jaridenv.2020.104244 [IF2019: 1.830]

The paper is open access and can be downloaded from the journal homepage.

The Steppe Marmot (Marmota bobak) is the largest member of the Marmotinae family. The species occurs in Ukraine, Russia and Kazakhstan, most typically in the steppe zone. Originally, this marmot is a characteristic steppe species, which lives in colonies and like many other steppe-inhabitant rodents, they also build a complex burrow system. The burrow is a central place in the life of marmots: it provides shelter from extreme hot and cold temperatures and also from predators. The underground part of the burrow can be as deep as 3 metres, while the aboveground part is usually a 0.5 - 0.8 m high mound. These marmot burrows are characteristic landscape elements in the steppes often giving the impression of an undulating surface.

Marmot burrows are characteristic elements of the steppe landscape.

Steppe Marmot (Marmota bobak).

The aim of our study was to test whether there are differences between the vegetation growing on the burrows and the intact steppe. Our study sites were situated in the Naurzum Nature Reserve, North Kazakhstan, in Stipa lessingiana dominated feathergrass steppes. The road from Hungary to Kazakhstan and the moments of our expedition were so exciting that we will give some impressions about them in a another blog post soon.

Stipa lessingiana  steppe in the Naurzum Nature Reserve.

On the following pictures you can see the two types of marmot burrows which we studied: on the lower-elevated steppes, which are sometimes inundated in springtime, the marmots build burrows with an approximately 60cm high aboveground mound; while on the higher elevated, seldom inundated sites, there are flat burrows. We compared the vegetation of the marmot burrows to that of the intact steppes. To complement our field survey, we performed a mini-review about the ecology of the Steppe Marmot, to establish links between the building and using of the burrows and the structure and species composition of the burrow vegetation.

Mounded burrow.

Flat burrow.

 

Both studied burrow types were actively used and inhabited by the marmots. The trampled surface around the entrance and the lot of flees were good indicators of the presence of the marmots.

We found that the burrows were characterised by distinct vegetation composition which was markedly different from the intact steppes. The mounded burrows were the driest habitats, we detected the lowest values of soil moisture content on them. Due to the dry habitat conditions and the regular trampling and manuring, the mounded burrows were characterised by the xerophyte steppe grass Agropyron cristatum and several ruderal species. It is very interesting, that these plants, growing on the mounded burrows were all identified as preferred forage items by Ronkin et al. (2009) who investigated the forage preferences of the marmots using a large number of potential forage species. The marmots spend most of their times on or in the very close vicinity of the burrows, this way they can quickly escape from predators (especially the Steppe Eagle) by hiding in the burrow.  Our results suggest, that by trampling, grazing and manuring the rodents maintain exactly that type of vegetation, which contain their preferred food items. These activities have analogues in human gardening activities: soil disturbance (an analogue of ploughing and harrowing), mediation of seed dispersal processes by bringing up buried seeds and endo- and epizoochorous seed dispersal (analogues of seed sowing), nutrient input (an analogue of manuring or fertilisation) and grazing (an analogue of pruning). Nevertheless, further studies are needed to reveal more details of these interesting mechanisms. Thanks to the constant disturbance, trampling, grazing and manuring, these 'marmot gardens' can be considered as green oases in the steppe, which can provide fresh and green forage for the animals, especially in the critical late summer fattening period. In late summer, marmots need to be prepared for the hibernation, despite the steppe vegetation is usually dried out in that period. That is why the fresh and green forage provided by the ruderal plants on burrows can be especially relevant in that period. These marmot gardens can also contribute to the maintenance of the populations and metapopulations of the preferred forage plants on the landscape scale by acting as stepping stones for them.

Weedy patch - which is a green oasis for the marmots. They can feed on the fresh and green biomass in late summer, in the fattening period before hibernation.

Steppe Eagle (Aquila nipalensis) are one of the reasons why the marmots build the burrows.:) The best strategy to escape from predators in these open landscapes is hiding in the burrows.

The flat burrows had markedly different vegetation from both the mounded burrows and the intact steppes. The dominant species on flat burrows were halophytes, such as Anabasis salsa, Kochia prostrata and Petrosimonia species. These species were not present in the intact feathergrass steppes and they were confined to the flat burrows that provided the open establishment microsites for them. The closest populations of these halophyte species were several tens of kilometres from our study sites. It is plausible that the marmots brought the halophyte seeds up from deeper soil layers - as the tunnel system can be as deep as 3 metres, seeds from former vegetation types can be activated by the rodents. Halophyte species are adapted to harsh and unpredictable environmental conditions where the favourable conditions for establishment are rare and unpredictable; thus, they often have a long-term persistent seed bank which is a favourable strategy under these conditions. In other marmot species, it was observed that the marmots often lick salt from the soil surface or mud. It is possible that the Steppe Marmots consume salt-accumulating halophyte plants in order to increase their salt uptake above their physiological minimum limit. However, this theory needs to be verified in the future.

Marked difference between the vegetation of the flat burrow vegetation with halophytes and the steppe with the dominance of grasses.

Halophyte plants on the flat burrows.

Our results suggest that Steppe Marmots are important ecosystem engineers in the Eurasian steppes. Their burrows can be considered as distinct habitat islands with a vegetation composition that developed and exists thanks to the activities of the marmots. Besides it is interesting how one organism can modify the local micro-environment, our results have further interesting implications on larger spatial and temporal scale. To illustrate the spatial relevance of the findings, let's take a look at the number of marmot burrows: according to the most up to date survey (Koshkina et al. 2019) there are approximately 1,200,000 actively used marmot burrows in Kazakhstan. Part of these burrows are situated on arable fields, as the land use changes of the past decades had considerable effect on the habitat use of the marmots. However, there are still several hundreds of thousands actively used steppic burrows! Besides the actively used burrows, there are also millions of abandoned burrows of a different age. These numbers illustrate well the magnitude and effect of burrow systems in steppe landscapes. From the descriptions of travelers from the 19th century, we can learn that in some steppe landscapes, marmot burrows covered more than 10% of the area, and gave the impression of undulating surface. Given the large numbers of burrows, it is plausible that they acted as stepping stones for the dispersal of plant species in the past and supported the colonization of new sites or even regions during climatic shifts.

Interesting outlook: kurgans (ancient burial mounds built by nomadic steppic tribes) are similar structures to marmot burrows. In these regions, the distribution, shape and size of kurgans are very similar to the burrows. On the picture, there is a kurgan - the similarity to the burrows is very striking. You can read our paper about kurgans in Kazakhstan by clicking here (Deák et al. 2017 Plant Ecology and Diversity).

Abstract

Burrow-dwelling rodents are often considered ecosystem engineer species in arid environments. They create distinct habitat patches by building burrows: they move large amounts of soil, mix soil layers and change soil properties locally. Our aim was to explore the role of Steppe Marmot as an ecosystem engineer in shaping the plant species composition and diversity of steppes. First, we made a literature search to gather information on the ecosystem engineering effect of the species. Second, in a case study, we compared the vegetation of marmot burrows with the surrounding intact steppes in North-Kazakhstan to identify differences in species composition and plant functional groups. Vegetation of the burrows was structurally and compositionally different from the intact steppe vegetation. Burrows were characterised by lower total vegetation cover, higher cover of annuals and lower cover of perennial grasses compared to the intact steppe. We found an increased cover of ruderal species on the burrows, but also several specialist species, such as Agropyron cristatum, Anabasis salsa, Kochia prostrata and Petrosimonia spp. were confined to the burrow vegetation. Our results suggest that marmot burrows increase the landscape-scale heterogeneity of the steppe vegetation and could act as stepping stones for the dispersal of several steppe-specialist species.

Finally, a group photo of our team :)

From the left to the right: Csaba Tölgyesi, András Kelemen, Balázs Deák, Orsolya Valkó, Róbert Gallé and Zoltán Bátori.

Observation of the marmots.