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This document provides an overview of alien species and evolutionary ecology. It defines key terms and outlines the history of the field. It discusses the large number and impacts of alien species introductions in North America, particularly their ecological and economic costs. It explores how the introduction of alien species can lead to rapid evolution in both alien and native species through processes like dispersal adaptation, establishment in new environments, and interactions with climate change. The document also notes conservation challenges around defining alien species in a changing climate.
Robinshin
- 1. Alien Species and Evolutionary Ecology
- 2. Outline • Introduction • Ecological and Economic Impact of Alien Species • Alien Species and Contemporary Evolution • Alien Species and Rapid Evolution - Dispersal - New Environments - Time lags - Climate Change - Conservation
- 3. Key Terms • Introduced: species that come from one location and brought to another • Exotic- same as introduced • Alien- same as introduced • Non-native: same as introduced • Invasive- species that becomes abundant and influences community process of native species • Pest- any species that is not wanted by humans
- 4. Brief History of the Field • 1958- Charles Elton- Pioneer of Invasion Biology, first to characterize introductions of plants and animals. However, did not promote wide spread research following his publications • 1970’s- Growing concerns of introduced species as threats to native biota, these studies focused especially on islands and long isolated biotas • 1980’s- Research expands greatly focusing on all biotas • 1990’s – new genetic analyses allow for the study for population genetics and evolutionary change • 2016- now a well-established field of ecology, subject of many international meetings, state and federal agencies seek funding to deal with alien species, Journal of Biological Invasions.
- 5. Some statistics on alien species • Most species introductions have occurred in North America • ~ 6,600 species of alien terrestrial, freshwater, and marine organisms – This is a conservative estimate, did not account for cryptic species, many organisms in Canada • In the U.S, alien sp. have caused or contributed to decline in ~ 49% of all species on the threatened or endangered species list. (wilcove et al. 1998) • The distribution of alien species across North America is not uniform - Discuss why this might be, and where you would expect to find the most alien species. - Hawaii- 4,600 alien species established - Florida and Gulf Coast- over 2,000 species established - West Coast- 674 species established - Tourism, International trade, suitable/ favorable habitats
- 6. Ecological and Economic Impact of Alien Sp. • Invasive alien species are recognized throughout the world as one of the most serious ecological and economic threat of this millennium ( Pimentel 2002) • Economic cost- $137.2 billion dollars annually (Pimentel 2000) • Discuss potential economic consequences of Alien species. • Alien species reduce productivity of agricultural crops, pastures, and rangelands • Disrupt natural waterways and alter function of freshwater and marine ecosystems • Ex- water hyacinth • N- South America
- 7. Ecological and Economic Impact of Alien Sp. • Ecological Impacts- Broadly speaking, alien species alter biotic structure of ecosystems and are pushing many native species to extinction • Additionally, Increased introduced diseases and their vectors are posing new threats to humans • Invasions likely to increase due to increased connectivity of human societies
- 8. Alien Species and Contemporary Evolution • The introduction of alien species is leading to rapid evolutionary change in both native and alien sp. • Contemporary in the sense that we are talking about scales of 10-100 generations rather than millions of years of evolutionary processes. • Why is this occurring? - primarily due to the profound human influence on the natural world ( Stockwell et al. 2003) • Alien Species introductions interact with habitat destruction and fragmentation, over-exploitation of resources, and global climate change • These interactions involve all groups of organisms and types of interactions: Plant- Herbivore, Prey-Predator, and Host-Pathogen
- 9. Adaptation of Alien Sp. For Dispersal • Dispersal ( process) – movement of individuals away from each other, or from home range ( Parent- Offspring, High density Low Density ) vs. • Dispersion ( Pattern)- spacing of individuals as a result of dispersal
- 10. Adaptation of Alien Sp. For Dispersal • Dispersal is a basic life history process for all organisms • Types of propagule dispersal: - Hydrochory- via water, invertebrate larvae and seeds - zoochory- via other animals, seeds - Anemochory- via wind, ballooning in spiders - Anthropochory- via humans • Propagule- seeds, spores, larvae – Ex. Ferns, dandelions, cottonwoods, milkweeds produce enormous quantities of spores carried long distances by wind • Alternative life-strategies to dispersal- Aestivation, Torpor, Hibernation, Desiccant Resistant eggs.
- 11. Adaptation of Alien Sp. For Dispersal • Dispersal is of central importance to alien species • In general, the best alien sp. have naturally good dispersal abilities, with combined effects of human assisted dispersal. • Overall, natural dispersal mechanisms play a small role in dispersal of alien species across large geographic barriers, however local invasions possible ( Mack and Lonsdale 2001)
- 12. Inadvertent Human Assisted Dispersal • Humans assume major role as unknowing agents of dispersal of plants, animals and microbes • On a local scale propagules may spread via- boats, cars, railroad trains, shoes of hikers, etc) • On a global scale, human assisted dispersal is responsible for the vast majority of intercontinental invasions, spread via cargo ships and airplanes • Seed contamination is also a inadvertent form of dispersal – Results from inefficient cleaning of seeds where non-natives get mixed with crop seeds – Agroecotypes- croplike weeds which show similar patterns of growth and reproduction that mimics crop plants ( Barret, 1983) – Are confined to stands of cultivated crops, and are often simply the weedy form of the crop plant itself
- 13. Inadvertent Human Dispersal • Agroecotype Example – Oryza sativa and Echinoloa crus-gallis- E. crus gallis species mimics the phenology, appearance, and seed morphology of the cultivated rice O.sativa
- 14. Dispersal by Deliberate Introduction • Characteristics that make plants and animals valuable and attractive to humans can also be seen as a “ preadaptation” of alien species for dispersal. • Crop, Forestry, and horticultural plants, domestic animals, exotic wildlife, and aquacultural fish have all gained access to new geographical areas due to their high human value. • Religious reasons, biological control, ignorance, ornamentals, sport • Hawaii- 57 % of all established species were deliberately introduced ( Wester 1992) • East Coast- 61% of established tree species before 1900 were deliberately introduced
- 15. Dispersal by Deliberate Introduction • Ex- Tamarix ( salt cedar)- deliberate introduction on east coast for aesthetic purposes • used to help stabilize streams and as windbreaks in south western states • Escaped cultivation and now vastly abundant and invasive • Use large amounts of water per day ( ~100-200 gallons) and outcompetes native riparian vegetation.
- 16. Few Examples of Rapid Evolution of Enhanced Dispersal • Cody and Overton (1996) – censused vascular plants on Barkley islands and Vancouver, BC • Noticed many cases of colonization and extinction on the islands • Colonization resulted from seeds that were wind dispersed from main land • Asked whether established plant seeds were same or different than ones on mainland, and whether seed structure changed over time for plants.
- 17. • Found that 2 of 3 plant species examined showed population age related differences on Barkley Islands • Discuss: What you think these age related differences may be. • For both plant species ( Hypochoeris and Lactuca), newly established populations showed smaller seeds than those of mainland plants • However, seed sized increased significantly with population age • Pappus volume also showed a tendency to decrease over time • Shows that intense selection pressure for heavier seeds with a smaller pappus once established on island.
- 18. Another Example • Two species of conehead bush crickets expanding range in England northward from southern coast ( Thomas et al. 2001) • Both species are dimorphic- Long-winged and Shortwinged • Found that regions colonized within the past 20 years show higher frequencies of the long-winged type than regions occupied for over 20 years. • Break
- 19. Adaptation of Alien Sp. To New Environments • Many pathways of adaptation once in a new environment • Differences in genetic variability influence the potential for evolutionary change. • Many techniques allow us to asses genetic variability between source and founder populations - Allozyme Analysis- oldest, least expensive, use of enzyme electrophoresis to detect genetic variation - DNA Fragment Length Polymorphism- use of restriction enzymes to cut DNA fragments - Restriction Fragment Length Polymorphism- best for examining variation within a species, determine if allelic variation exists for a particular gene - Microsatellite Analysis- non-coding repeated sequences of DNA, look at mutation rates of non-coding regions as well as number of microsatellites in a particular region - Mitochondrial DNA- circular DNA, also has non-coding region that is highly variable and has high rate of change.
- 20. Adaptation of Alien Sp. To New Environments • Back to genetic variability… • Genetic variability varies greatly among alien species. • Founder Effect- occurs when few founder individuals from a limited part of their native range contain only a fraction of genetic variability compared to the whole source population – Over time, coupled with the effects of genetic drift, this effect could lead to the complete loss of variation in the population ( Allendorf 1996) • Thus the size of the founding population and its’ growth rate are very important determinants of genetic variability in alien populations
- 21. Adaptation of Alien Sp. To New Environments • Ex- European starling ( Sturmus vulgaris) • This bird species provides a good example of the founder effect, but also how low variability does not necessary limit the success of all alien species. • One hundred individuals introduced in NYC in 1890. (Cabe 1998) • Using allozyme analysis- showed that N. American populations lack ~42% of alleles which show variability in Europe. • Additionally, starlings within N. America show little to no variation, yet these species are highly abundant across the U.S
- 22. Time Lags and Alien Species • Many alien species show a substantial time lag ( years to decades) between initial establishment and appearance of ecological impacts on communities ( Crooks and Soule 1999) • Ecological Reasons- simply, a species may need time to disperse into favorable habitat patches, and to build up population numbers • Allee Effect- when low initial population density restricts or hinders population fitness due to the lack of social interactions ( mating systems) • Ex- this effect is believed to explain the time lag between initial establishment of house finches in NYC in 1940, to eventual abrupt population increase in 1960. Highly social birds, require interactions for mating ( Veit and Lewis 1996)
- 23. Time Lags and Alien Species • On the other hand, initial populations may lack evolutionary adaptations which limit their population growth. After some time period and after undergoing selection, evolutionary breakthrough may be possible • Ex- Ragwort ( Senecio inaquidens) , a switch to earlier flowering apparently enabled the species to become highly invasive in Europe ( Kowarik 1995) • Additionally, hybridization between species or b/t populations of different species may also result in a time lag before rapid population growth
- 24. Evolution by Alien sp. and Climate Change • Alien invasions are being compounded by global climate change(Mooney and Hobbs 2000) • Many aspects of climate change- warming, atmospheric co2 increases, ultraviolet radiation intensity, deforestation, desertification, ocean acidification. • These changes strain adaptation of native species to conditions they have long been adapted for. • Generally, these conditions make it easier for alien invasions • The “stress” of climate change puts ecological communities in disequilibrium, these conditions favor species with short life spans, high dispersal abilities, rapid population growth and opportunistic behaviors ( Barret, 2000) • Fragmented habitats are more likely to favor species with high dispersal and colonization capabilities ) ( Barrett 2000)
- 25. EPA.gov
- 26. Evolution by Alien sp and Climate Change • However, alien species can also influence climatic change ( Mack et al. 2000) • Ex. The deliberate introduction of African tropical pasture grasses into the Amazon basin has the potential to change regional climate by altering fire frequency intervals • Discuss: The potential mechanism behind this change. ( Think of successional processes) • African pasture grasses are high fuel plants • Produce high heat and fast burning fires. • Flammable grasses are capable of converting forest areas into grasslands and savannas
- 27. Woody vegetation Land Clearing + Introduction of grassesFIRE Selection for grasses grassland/savanna positive feedback due to rapid regrowth, flammability, and microclimate feedback
- 28. Alien Sp and Conservation Concerns • Major issue is trying to define what is and what is not an alien species. • Climate change has and will continue to shift the ranges of many species into habitats that were previously unsuitable. • What do we regard as an alien species? • Should species be considered alien if they occupy new ranges due to climate change that make these new areas suitable? • Also, considering that responses to changing environmental conditions have always occurred at some process, and is in some sense natural. • What should our conservation goals be ? • should it be to confine species to their native ranges at some time period, despite a changing climate ? • Is it time to change the way we view ecological communities? - are ecosystems really as intricate, highly evolved, and in natural balance as we think they are? - or should we view them as more as snap shots in time which show us a set of general relationships and patterns at a particular point of time. Organisms in a community are there simply because they thrive ( Ecological fitting rather than lock and key), ecological change is the norm, not the exception
- 29. Next time… • Maybe: source populations, cryptic species, invasion resistance, native extinction/extirpation/endangerment, hybridization and transgenic organisms, • Or Plant-herbivore interactions • Homework Assignment- find a alien species currently in North America – Briefly describe its life history and ecology – What is its’ native range ? – What is its’ current range? – Potential ecological and economic threats ?