Importance of Flight for Habitat Occupancy a Pilot Study on American Ground Beetles
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Importance of Flight for habitat occupancy A pilot study on American Ground Beetles Alexander Irwe Degree project for Bachelor of Science in Biology BIO602 Biology: Degree project 15 hec Spring 2015 Department of Biological and Environmental Sciences University of Gothenburg Examiner: Christer Erséus Department of Biological and Environmental Sciences University of Gothenburg Supervisor: Urban Olsson Department of Biological and Environmental Sciences University of Gothenburg Frontpage photo by: Jeffrey S. Pippen Macon Co. NC12 May 2006 Table of content Abstract…………………………………………………………………1 Introduction……………………………………………………………..2 Material and Methods…………………………………………………3 Results………………………………………………………………….5 Discussion………………………………………………………………5 Table 1 and 2…………………………………………………………..6 Acknowledgements……………………………………………………8 References……………………………………………………………..9 Abstract Insects are one of the oldest groups of terrestrial animals still living today and were the first to evolve wings. Since then insects have evolved into many different shapes and sizes and occupy a wide range of niches. One group of insects, the Carabidae or ground beetles are interesting as they contain both species with good flight capacity and species with reduced wings that have lost the capacity to fly. The genus Cicindela is a group of ground beetles that have a larger than average flight capacity of most beetles. Carabus on the other hand is a genus were most of the species have reduced wings and lack the ability to fly. There is both cost and benefit in having flight capabilities and one benefit would be quicker and better movement. The assumption that flying species would better disperse themselves could be tested by comparing fundamental niche usage between two groups that differ in flight capabilities. To test this occurrence data of species from the Carabus and Cicindela genera were retrieved to calculate their realized niche, and Ecological niche modelling (ENM) was done to project their fundamental niche. The difference in realized and fundamental niche area was calculated for both genera and statistical tests were performed. The results indicate that Cicindela occupies a larger proportion of their fundamental niche than Carabus but the results from the statistical tests were not conclusive. A significant difference between the two genera was only seen when looking at the proportional difference but not when looking at the difference in real values. More species and further refinement of the ENM could help to increase confidence of the test. Abstrakt Insekter är en av de äldsta landlevande djur som fortfarande lever idag och var de första som utvecklade vingar. Insekter har sedan dess utvecklats till många olika former och storlekar och ockuperar en mängd olika nischer. En grupp av insekter, Carabidae eller jordlöpare är en intressant grupp då de innehåller både arter med god flygförmåga och arter med reducerade vingar som har förlorat sin förmåga att flyga. Släktet Cicindela är en grupp jordlöpare som har en flygförmåga över det vanliga för de flesta skalbaggar. Carabus är istället ett släkte där de flesta arter har reducerade vingar och saknar flygförmåga. Det finns både för och nackdelar av att kunna flyga och en fördel är att kunna förflytta sig snabbare och lättare. Antagandet att flygande arter skulle ha lättare att sprida sig kan testas genom att jämföra fundamental nischanvändning mellan två grupper med olika flygförmåga. För att testa detta hämtades data på förekomst av arter från släkterna Carabus och Cicindela för att sedan räkna ut deras realiserade nisch. ”Ecological niche modelling” (ENM) användes för att projicera arternas fundamentala nisch. Skillnaden mellan realiserad och fundamental nisch area räknades ut och stat istiska tester utfördes. Resultaten visar på att Cicindela ockuperade en större andel av sin fundamentala nisch än Carabus men resultaten från de statistiska testen var inte fullt övertygande. En signifikant skillnad mellan de två släkterna sågs endast för den proportionella skillnaden men inte för den faktiska skillnaden. Fler arter och mer finputsning av ENM kunde hjälpa till att öka säkerheten av undersökningen. 1 Introduction in almost all types of environments and can be found all around the globe. Most of them are carnivores (Lövei et al, Insects were one of the first animals to 1996) but some species seem to be invade land some 400 million years ago omnivores or even frugivores (Hill et al, which created many new opportunities 1992). A lot of species have lost their for insects to adapt to new niches ability to fly or have reduced wings (Grimaldi et al, 2005). Since then insects (Lövei et al, 1996) but many species of have adapted to a number of different the genus Cicindela or common tiger environments and evolved many types beetle which is part of the Carabidae of features. The ability to fly was first family can still fly (Carter, 1989). Another evolved by insects sometime in the large group of ground beetles is the Carboniferous time period and has since genus Carabus in which most species then evolved in many different species lack functional wings (Lindroth, 1986). and groups of animals (Knecht et al, Most ground beetle species seem to 2011). Flight allowed for rapid movement have similar habitat and food preference to catch pray, avoid being caught or to (Lövei et al, 1996), so the major reach new otherwise inaccessible difference between the Carabus and habitats. Flying is costly since it requires Cicindela genera are the flight a lot of energy to remain airborne, so for capabilities. it to evolve the benefit has to outweigh the cost of maintaining the ability to fly One can then assume that species from (Roff, 1986). When studying newly the Cicindela group would be much formed habitats such as islands made more proficient in finding new areas with from volcanic activity, species with flying suitable habitats. Since most of the capabilities and plants with air-travelling Cicindela species still have functional seeds and pollen are usually the first wings it would be assumable that they ones to settle in the newly formed have an easier way to disperse habitat. Interestingly enough, islands themselves. One possible way of testing and other isolated habitats have a this would be to calculate the area of the proportionally larger number of species realized niche for the species in each without flight capabilities than inland group and then calculate the area of the habitats. This suggests that selection fundamental niche for each species. pressure for flight may decrease in Realized niche in this case refers to a isolated islands (Gillespie, 2007). The species current niche where it actually term brachypterous is used to describe resides and fundamental niche refers to the loss of or reduced wings in animals a species potential niche were it could and can be seen throughout the Insecta live (Sadava et al, 2011). A species lineage. Some species have both realized niche is usually smaller than its winged and brachypterous morphs in a fundamental niche as it might be population and are thought to be an restricted from a number of factors such adaptation depending on the stability of as competition from other species or the environment or a trade-off from other migration hinders. If Cicindela species features (Roff, 1986). One obvious are better at dispersing they would use drawback from wing reduction is the loss their potential habitats to a higher extent in mobility and perhaps the potential than species from the Carabus genus. In ability to disperse. this study I gathered information on the current distribution and compared it to One interesting group of insects are the the potential distribution estimated by ground beetles Carabidae which today Ecological niche modeling. The test is to have more than 40,000 species see if flight capability has a positive described (Erwin, 1985). They are found 2 effect on the ability to disperse. The null points together with environmental data hypothesis is that no difference in to model the species fundamental niche relative utilization of available habitat over a geographical area (Kearney, exists between two groups of different 2006). Before the initial ENM was done flight capabilities. A difference would a trial and error phase was conducted to violate the assumptions of the null see which environmental layers were to hypothesis and indicate that flight is be used in the final model. This was important for the ability to colonize all done using a custom made workflow areas of suitable habitat. based on jackknife resampling that test which of the chosen layers affected the Material and Methods model the most (Leidenberger et al). The layers that had the biggest effect were Occurrence data retrieval and considered most important for the Ecological niche modelling accuracy of the model. Correlation tests using ENMtools For this study 10 species of each ground (http://enmtools.blogspot.se/) were also beetle genus Carabus and Cicindela conducted to make sure none of the were used, giving a total of 20 species. layers correlated with each other. If any More species would have been selected layers correlated the one that had the but there was a limited number of lowest effect from the jackknife tests was Carabus species with occurrence data removed. The environmental layers available. North America was selected selected by the jackknife and correlation as an area of interest since it has a lot of tests were: annual mean temperature, well documented records of species and precipitation of driest month, is a relatively large area with no large temperature annual range, bulk density, expanses of water interfering with salinity, gravel content, ph and altitude in species migration. The selected species meters. Studies on ground beetles were chosen by looking at which of them suggested that humidity would be a had the most available data from the limiting factor for habitat preference Global Biodiversity Information Facility (Lövei et al 1996) which coincides with (GBIF) (http://www.gbif.org/). The the precipitation of driest month layer in occurrence data for each individual the model.