For the past several years, given involvement in the University of Georgia Citizen Science Monarch Health Project, Monarch decline has been observed. Numbers of Monarchs are measured in ‘hectares’ of Mexican forest they inhabit while overwintering. The decline in Monarch hectares from 1996 (18.9 hectares) to 2020 (2.83 hectares) is 85%.
How many migrating butterflies are estimated to remain? To estimate the loss, well-known Biologist and Monarch specialist Dr. Lincoln Brower counted dead butterflies resulting from a 2002 winter storm in which most overwintering monarchs were killed (Journey North, n.d.). Counting those deceased and approximating those still on the trees in a representative area, Dr. Brower identified that approximately 50 million overwintering Monarchs filled one hectare of Mexican forest. Using the Journey North data and Dr. Brower’s calculations, the current estimate of migrating monarchs left for us to care for is 141 million, a rather significant reduction from the 945 million in 1996. Reviewing the book, The sixth extinction: An unnatural history (Kolbert, 2014), I wonder if there is a “Sixth Mass Extinction “process and if this decreasing butterfly population is part of it?
Categorization of what a mass extinction is depends upon the magnitude of biodiversity loss based on geological record; currently identified as a loss of more than three-quarters of species in a short geological time frame, identified in millions of years ago (Mya). (Barnosky et al., 2011). Though criteria categories leading to extinction risk and how that is determined may differ between organizations (example: IUCN Red List Categories (International Union for Conservation of Nature and Natural Resources [IUCN], n.d.) and Texas (Texas Parks and Wildlife [TPWD], n.d.) and researchers, (Cowie et al., 2017), (Briggs, 2017)Briggs, Wake & Vrendenberg (2008) and others, consensus about actions needed are the same. Action that promotes continuance of small or rare populations of species should be taken.
The “IUCN Red List”, or the International Union for Conservation of Nature, is used by multiple organizations as a list of species on which data has been gathered for determination of species risk. Currently the species on which data has been collected is a small percentage of the species that have been identified and named (Barnosky et al., 2011). The Red List partnership includes multiple national and international organizations and universities including Texas A&M University (IUCN, n.d.)
“Why is there mention of a ‘Sixth Extinction’? In the history of the world, five ‘Mass Extinctions’ of species have been identified through geologic records.”
Rosemary Plank
Why is there mention of a ‘Sixth Extinction’? In the history of the world, five ‘Mass Extinctions’ of species have been identified through geologic records. Wake and Vredenburg (2008), state that the magnitude of first two extinctions, called the Ordovician-Silurian extinction and the Late Devonian extinction (444 million and 383-359 million years ago respectively) were not as significant as the three following, and might be identified as a depletion of magnitude (Barnosky et al., 2011). The cause of extinctions during this time were nature driven, primarily sea level fluctuations and global warming.
The three extinctions that followed were the Permian-Triassic (251 Million years ago or Mya), End Triassic (199-214 Mya), and Crustaceous-Tertiary (65 Mya). The Permian-Triassic had the greatest rate of extinction, with 95% of all species (including plants) being lost. All of these extinctions were due to ‘natural’ changes such as volcanic activity and sea oxygen loss (Wake & Vredenberg, 2008).
The current “Sixth Extinction”, the one which potentially began 11,000 years ago (Wake & Vredenberg, 2008); Briggs (2017), is thought primarily due to human presence. Briggs (2017), questions the verification of the assessment of human action being the cause of the sixth mass extinction by noting that there is currently no way to differentiate between natural and human causation because reported extinction research has been primarily measured on isolated island species and biodiversity gains during the period studied has not been calculated.
Verner believes the ‘Sixth’ may be “one of the fastest (growing) extinction rates of all time.”(Verner, 2015, p. 214). Briggs (2017, p. 122) states that we must collect “evidence that the global biodiversity is decreasing due to a rise of extinctions above the rate of speciation”. Scientists attempt to create graphs using current and past data, both hypothetical and actual, and project it into the future to identify species loss percentages. Due to extinction rate identification over lengthy time periods, extinction percentages hypothesized for the future vary widely (Barnosky et al., 2011)(Briggs, 2017).
Species that have not become extinct but have been reduced to ‘remnant’ populations and influence the overall state of biodiversity, such as butterflies, tiger beetles, dragonflies, damselflies, should be of greatest concern to today’s conservationist. Given their remaining numbers, IUCN data, general consistency of findings, primary roles in determination of ecosystem health and past and current focus of public and conservationists attention influence the effort and potential desire of public to interact with the remnant species. Can we Master Naturalists affect possible extinction of species populations currently identified as remnant, at risk, threatened, or endangered? Tallamy (Darke & Tallamy, 2014)(Tallamy, 2019)(Tallamy, 2009), Briggs, (Briggs, 2017), Verner (Verner, 2015)(Barnosky et al., 2011) and multiple others believe we can and we should.
Extinction Mitigation
Tallamy identifies an issue with attempting to control extinctions through park systems, preserves, wilderness areas and governmental controls; they are necessary, but not sufficient. Tallamy states “.. we will not succeed if we continue all of our conservation efforts to patches of protected areas. Parks and preserves are central to any large-scale conservation effort, but they will never be enough because they are not large enough and they are not connected to one another.(Tallamy, 2019, p. 35)” Some large groups are attempting to build ‘corridors’ for connectivity. Habitat fragmentation occurs when a large piece of land is divided into smaller sections which no longer represents the original. Think of your yard, it used to be part of a larger land section that was divided up in small sections for homes. The plants and habitats for small insects and animals were scraped away and each yard became a disconnected singular space that no longer supports the natural and healthy eco-region it was once a part of.
Habitat connectivity through creating corridors is vital whether between small or large spaces. When constructing a 56-mile highway in Montana, 39 wildlife crossings were included to reduce automobile/animal accidents and to facilitate animal movement within their original habitat area (Andis et al., 2017). Images of crossings are seen at https://www.google.com/search?rlz=1C1CHBF_enUS724US724&source=univ&tbm=isch&q=images+of+animal+crossings+along+56+mile+highway+in+Montana,&sa=X&ved=2ahUKEwioj924noTqAhUPTKwKHUI1DkIQsAR6BAgKEAE&biw=1920&bih=920).
Habitat corridors can be built between small sections of land such as urban yards or lots. These lots should include native plants in support of insects, vertebrates, etc., that are historically native to the region (Tallamy, 2019). Native plants that support multiple native insect species such as butterflies, dragonflies, some beetles, and damselflies (Tallamy, 2019)(Briggs, 2017), called keystone plants (Tallamy, 2009, p. 139), are primary due to their being a cornerstone to a healthy local ecosystem and its’ food web
Where to Start?
Reviewing the list of species that are on Texas Parks and Wildlife and the IUCN web sites as remnant populations help us to identify native plants that support the species. The plant identified may supportive of itself i.e. be a plant that feeds the larva of the desired at-risk insect, or supportive given its’ place in the food web i.e. grows the larva that feeds the remnant bird population desired in the landscape. Which native plants are used depends upon the objective or purpose of the individuals owning the land. If the purpose is to increase the butterfly and dragonfly populations, the landscape configured will have a water space for dragonflies and puddling space for Monarchs (that a neighbor wants to raise). Landscapes generally have the food for dragonflies that includes gnats, mosquitoes, black flies and house flies. A native goldenrod (genus Solidago), which serves generalist insects for the purpose of nectaring and laying eggs, supports 181 species of caterpillars and is much appreciated by migrating birds.
Before contact is made with others in a community, neighbors, nursery’s, landscape companies, home owner associations, to discuss and promote plant and insect corridors, native plant species for the area served are identified along with the major insect populations they support. From there, documentation of plants in the Master Naturalist yards occur and questions asked, answered, and shared
- what is the objective or goal as it relates to at-risk species in our area;
- what plants are present, are they native or non-native;
- what insects do the plants support; are they for insects that larva on only one type of plant such as our monarchs or do they support many insect species;
- what are the keystone plants;
- what eco-system conditions are appropriate for the objective and purpose;
- what actions are taken to promote or reduce spread of plants that we have;
- what plants that are NOT native are kept and for what purpose;
- what purpose does the plant serve in the yard,
- how are not-wanted insects managed
A chart is used and shared for the documentation of the plants present and changes based on the objective and goals planned for what should change to support a healthy eco-system.
Once this is done, neighbors and organizations in the community are provided with education and assistance for planning change according to their desired objectives for yards belonging to them. The pond in the garden for dragonflies has a puddling area for a neighbors Monarchs and a nectaring plant that they love. His yard has specialist native plants for milkweed specific butterflies and Texas grasses – thus a corridor is created for the remnant species to live and reproduce.
Rosemary Plank, Texas Master Naturalist
References
Andis, A. Z., Huijser, M. P., & Broberg, L. (2017). Performance of arch-style road crossings structures from relative movement rates of large mammals. Frontiers in Ecological Evolution, 1– 13. https://doi.org/10.3389/fevo.2017.00122
Barnosky, A. D., Matzke, N., Tomiya, S., Wogan, G., Swartz, B., Quental, T. B., Marshall, C., McGuire, J. L., Lindsey, E., Mcguire, K. C., Mersey, B., & Ferrer, E. A. (2011). Has the earth’s sixth mass extinction already arrived?. Nature, 471, 1–19. https://doi.org/10.1038/nature09678
Briggs, J. C. (2017). Emergence of a sixth mass extinction?. Biological Journal of the Linnean Society, 122, 243–248.
Cowie, R. H., Regnier, C., Fontaine, B., & Bouchet, P. (2017). Measuring the sixth extinction: What do mollusks tell us?. The Nautilus, 131(1), 3–41. Retrieved May 10, 2020, from
Darke, R., & Tallamy, D. (2014). The living landscape. Timber Press. https://doi.org/ISBN 978-1-60469-408-6
International Union for Conservation of Nature and Natural Resources. (n.d.). The IUCN red list of threatened species. The IUCN red list of threatened species. Retrieved May 30, 2020, from https://www.iucnredlist.org/
Journey North. (n.d.). Estimating the number of butterflies in a colony [ND]. Journey North: Monarch Butterflies. Retrieved May 12, 2020, from https://journeynorth.org/tm/monarch/PopulationMexicoPerHectare.html
Kolbert, E. (2014). The sixth extinction: An Unnatural history. Henry Holt. https://doi.org/13: 978-0805092998
Tallamy, D. W. (2009). Bringing nature home: How you can sustain wildlife with native plants (2nd ed.). Timber Press. https://doi.org/ISBN: 0881929921
Tallamy, D. W. (2019). Natures best hope:A new approach to conservation that starts in your yard. Timber Press. https://doi.org/ISBN 978-1-60469-900-5
Texas Parks and Wildlife. (n.d.). Federal and state listed species in Texas. Federal and State Listed Species in Texas. https://tpwd.texas.gov/huntwild/wild/wildlife_diversity/nongame/listed-species/
Verner, L. (2015). Ecological concepts. In (pp. 183–217). Texas A&M University Press . https://doi.org/ISBN 9781623493400
Wake, D. B., & Vredenberg, V. T. (2008). Are we in the midst of the sixth mass extinction? A view from the world of amphibians. Proceedings of the National Academy of Sciences of the United States of America, 105(suppl. 1), 11473 –11473. Retrieved April 2, 2020, from https://doi.org/10.1073/pnas.080 1921105