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Shrubs and invasive grass predict lizard occurrence in an arid shrubland
- 1. The realized niche of the endangered blunt-nosed leopard lizard (Gambelia sila) is determined by interactions between native shrubs and invasive annual grass. Alessandro Filazzola, Westphal M., Powers M., Liczner, A.R., Johnson, B. & Lortie, C.J.
- 2. Filazzola & Lortie 2014
- 3. Lortie et al. 2015
- 4. Bruno et al. 2003
- 5. Lortie et al. 2015
- 6. Direct Thermoregulation Territory landmark Shelter Intermediary species Indirect Increase food availability Protection from predators Burrows
- 8. Distributional records for blunt-nosed leopard lizard USFWS 1998 Ciervo-Panoche Natural Area Carrizo Plain National Monument
- 9. Hypothesis: Plant-interactions either positive from shrubs or negative from invasive grasses can scale to other trophic levels such as lizards.
- 10. P1: Lizard presence relatively higher in shrubs than open microsites especially shrubs with high canopy cover P2: Burrows & trails are more frequent in shrubs and strongly predict lizard occurrence. P3: Lizards occurrence will be more frequent in areas of high shrub density and low annual cover (RDM)
- 12. Methods
- 13. Methods Shrubs Dimensions Volume Canopy cover Burrows Trails Scat Annual cover Residual dry matter weight
- 14. Methods
- 15. Data analyses Ordinary kriging -> for interpretation of intermediary points Statistical tests -> Logistic regression Auto-correlation -> Getis-Ord cluster analysis
- 16. Microscale results = 1.87; max = 7 p < 0.001
- 18. Microscale results N.S. Length Height Volume Trails Burrows P < 0.001 Canopy RDM
- 20. P1: Lizard presence relatively higher in shrubs than open microsites especially shrubs with high canopy cover P2: Burrows & trails are more frequent in shrubs and strongly predict lizard occurrence. P3: Lizards occurrence will be more frequent in areas of high shrub density and low annual cover (RDM)
- 21. + - + ?
- 22. Conservation & management 50% of shrubs from 2013 also had scat in 2014 Lizard families from the previous year The “Perfect” shrub
- 23. Conservation & management Lizards have short home ranges, 2-4 hectares (Warrick et al. 1998)
- 24. Implications for ecology Shrubs may be integral in structuring animal communities
- 27. Implications for ecology Shrubs may be integral in structuring animal communities Shrubs extend the realized niche for animals
- 29. Implications for ecology Shrubs may be integral in structuring animal communities Shrubs extend the realized niche for animals “Facilitation renaissance”
- 31. Thank you!! The Ecoblender lab BLM Hollister Field Office Deborah Woollett The Working Dogs’ crew Tia, Orby, Seamus
Editor's Notes
- Introduction:
- The focal species here is the endangered blunt-nosed leopard lizard (Gambelia sila). Because its habitat is in decline, there has been a large push to better understand the habitats they currently populate. The leopard lizard is carnivous eating mostly insects, and so does not rely on plants for nutrition, yet vegetative composition strongly may still strongly relate to their abundance.
- The currently distribution of the BNLL is to these areas within the San Joaquin Valley. The question then becomes, what makes these habitats ideal for the leopard lizard.
- The purpose of this project then was to resolve the effect of the shrubs on the leopard lizards. The shrubs are native and thus co-evolved with the BNLL, thus it is unlikely the shrubs are responsible for their population decline. Moreover, there has been preliminary evidence of lizards being frequently seen and captured under shrubs.
- P1: Lizard scat will be more frequently observed in shrub microsites, particularly those with high canopy. P2: Animal burrows and trails will be greater under shrub microsites and will strongly predict lizard scat occurrence. P3: Areas of high shrub density and low annual cover (RDM) will have the highest frequency of lizard scat.
- P1: Lizard scat will be more frequently observed in shrub microsites, particularly those with high canopy. P2: Animal burrows and trails will be greater under shrub microsites and will strongly predict lizard scat occurrence. P3: Areas of high shrub density and low annual cover (RDM) will have the highest frequency of lizard scat.
- What we have currently then is this interplay between the dominant shrubs in the system, the invasive grasses and our BNLL. What we know for certain is that the shrub positively increases the invasive grasses and that these grasses have a detrimental impact on lizard. What we don’t know is the role the shrubs play on the leopard lizard. Is there an indirect effect of the shrubs increasing the grasses which hinders the leopard lizard, or is there more of a direct effect by the shrub on the leopard lizard. Is the effect positive or is it negative? It is determining these missing link in this interaction web that will significantly assist conservationists in managing the BNLL.
- Half of shrubs from 2013 also had scat in 2014. I believe this could have two possible explanations. The first being that they are the returning lizard family from the previous year. These lizards species live for two or more years so it may be expected that they treat one as a consistent home for themselves. However, this assumes that the lizards associate with only one shrub, so this may not entirely be true. What I think to be more likely what is going on is the “perfect shrub” concept. These are shrubs that consistently have certain traits that we most likely see re-occurring scat even decades into the future.
- Lizards have short home ranges and our study area was around 120 hectares in size. This means that the lizards found within the defined groups here are unlikely to be moving around beyond these areas easily. If we were to clear the entire plateau of grass, it may take a while for the lizard population to expand beyond their current areas.
- Shrubs may be integral in structuring animal communities, by providing shelter to more than
- What was tested in the paper was this pathway, but the real picture is more complicated than that.
- Shrubs interacting with multiple animal and plant species functioning as the structure or keystone species for a desert community.
- This may be the beginnings of a renaissance for the study of positive interactions. What originally started in the late 90s as counting plants on and off dominant plants like cushions or shrubs, has now evolved into a explicit theory and large scale manipulations. This study is one of the first extending the work of plant-facilitation studies to see the impacts on animals and how shrubs may be positively maintaining lizard populations. The role of shrubs in affecting animal populations is obviously less clear because animal movement is more complex, however observing a higher frequency of scat in the shrubs does say that it plays some role in affecting lizard behaviour. Hopefully this will extend further research to better elucidate the mechanism of facilitation between shrubs and animals. If it is thermoregulation, this would be a critical finding given the blunt-nosed leopard lizard being an endangered species and the current climate shift that are occurring globally.
- Shrubs, as observed with plants, can extend the realized niche beyond that of the fundamental through habitat amelioration. This is particularly important for lizards because it increases the temperature heterogeneity of a desert area. Lizards may require these shrubs to assist in thermoregulation and may act as a buffer against climate change. However, with the predicted increase in climate for southern California, it may be expected that lizards are spending more time in shrubs to stay cooler. This change in behaviour may negatively affect the lizard by reducing foraging time and increasing predator susceptibility such as by snakes which hide in the shrubs.
- This may be the beginnings of a renaissance for the study of positive interactions. What originally started in the late 90s as counting plants on and off dominant plants like cushions or shrubs, has now evolved into a explicit theory and large scale manipulations. This study is one of the first extending the work of plant-facilitation studies to see the impacts on animals and how shrubs may be positively maintaining lizard populations. The role of shrubs in affecting animal populations is obviously less clear because animal movement is more complex, however observing a higher frequency of scat in the shrubs does say that it plays some role in affecting lizard behaviour.