Conservation Biology - Topic 16 PDF

Topic 16 Conservation biology Learning Outcomes Predict the fate of a population based on changes in population size, genetic diversity, and inbreeding depression. Suggest conservation strategies to overcome challenges faced by declining populations. Calculate the effective population size...

Topic 16 Conservation biology Learning Outcomes Predict the fate of a population based on changes in population size, genetic diversity, and inbreeding depression. Suggest conservation strategies to overcome challenges faced by declining populations. Calculate the effective population size of a population based on the number of active breeders and make recommendations to natural park managers. Justify the “no intervention” policy in national parks using arguments based on ecological principles Classify conservation strategies depending on the level of diversity they primarily target. Justify the importance of protecting biodiversity Identify taxon that are at risk based on population ecology criteria Describe how human activity can impact ecosystem communities Explain how species may not be able to cope with climate change 2  Topic 16 Conservation biology 16.1 – Extinction vortex and effective population size Extinction vortex Small populations (such as those going through a bottleneck) are prone to extinction because they are vulnerable to inbreeding and genetic drift. In addition to the lower fitness due to inbreeding (inbreeding depression), the reduction of genetic variability prevents the population from adapting to its changing environment. This reduces the population size even further in an extinction vortex (positive feedback loop). 4 Extinction vortex Small populations (such as those going through a bottleneck) are prone to extinction because they are vulnerable to inbreeding and genetic drift. In addition to the lower fitness due to inbreeding (inbreeding depression), the reduction of genetic variability prevents the population from adapting to its changing environment. This reduces the population size even further in an extinction vortex (positive feedback loop). Greater Prairie Chicken (Tympanuchus cupido) In 1993, to counter the decline in population size due to a decrease in fertility, researchers have introduced 271 individuals from larger populations and increased genetic variation. The population rebounded quickly out of the extinction vortex. 5 Effective population size Effective population size of a population (Ne): size of an idealised randomly mating population that shows the same level of heterozygosity as the population of interest. Heterozygosity: fraction of individuals in a population that are heterozygous for a particular locus. 6 Effective population size Effective population size of a population (Ne): size of an idealised randomly mating population that shows the same level of heterozygosity as the population of interest. Heterozygosity: fraction of individuals in a population that are heterozygous for a particular locus. Effective population size (Ne) = actual population size (N) if… The population has a balanced (1:1) sex ratio All individuals contribute equally to the next generation (same number of mating and offspring) Simultaneous birth of each new generation The population size remains constant over time 7 Effective population size Effective population size of a population (Ne): size of an idealised randomly mating population that shows the same level of heterozygosity as the population of interest. Heterozygosity: fraction of individuals in a population that are heterozygous for a particular locus. Effective population size (Ne) = actual population size (N) if… The population has a balanced (1:1) sex ratio All individuals contribute equally to the next generation (same number of mating and offspring) Simultaneous birth of each new generation The population size remains constant over time … but often… not all individuals contribute equally to the next generation  The effective population size (Ne) will then be less than the actual population size (N), heterozygosity and genetic diversity will be decreased  The population behaves (in terms of drift and inbreeding) as if it was much smaller than the census size! 8 Effective population size Effective population size of a population (Ne): size of an idealised randomly mating population that shows the same level of heterozygosity as the population of interest. Heterozygosity: fraction of individuals in a population that are heterozygous for a particular locus. Effective population size 4 × 𝑁𝑓 × 𝑁𝑚 Effective population size (Ne) = actual population size (N) if… 𝑁𝑒= The population has a balanced (1:1) sex ratio 𝑁𝑓 +𝑁𝑚 Number of Number of All individuals contribute equally to the next generation breeding females breeding males (same number of mating and offspring) Simultaneous birth of each new generation The population size remains constant over time … but often… not all individuals contribute equally to the next generation  The effective population size (Ne) will then be less than the actual population size (N), heterozygosity and genetic diversity will be decreased  The population behaves (in terms of drift and inbreeding) as if it was much smaller than the census size! 9 Effective population size Conservation programs often focus on maintaining the Minimum Viable Population size (MVP = smallest size at which a population is able to sustain its number and survive). MVP takes into account Ne, individual range, mortality rate, reproductive age… E.g. Grizzly bears in the Yellowstone Park (2020). Not all males breed as some males are dominant during the breeding season (male-male competition, unbalanced sex-ratio). N = 700 and Ne = 175 bears = 25% of N! … but 100 bears only would mean a 95% chance that the population survives 200 years. The introduction of 2 unrelated individuals per decade would be enough to reduce the loss of genetic diversity by half. 10 Effective population size E.g. Polar bears (Ursus maritimus) in the southern Beaufort Sea, Alaska (2006) Population size: N = 1526 Female-biased sex ratio: 54% (824) females… so 46% (702) males. Only 18.3% of females are active breeding females and 18.2% of the males are active breeding males Calculate Ne! Cronin et al 2009 11  Topic 16 Conservation biology 16.2 – Human impact on biodiversity Threats to biodiversity Habitat loss: changes in habitat (fragmentation, conversion to agricultural land or urbanisation) can affect species unable to disperse or adapt. Invasive species: species introduced accidentally can affect communities and native species distributions, increase competition for resources, predation or parasitism. Overharvesting: extensive exploitation (hunting, fishing, harvesting) can prevent the population’s ability to rebound. Pollution: accidental or excessive release of nitrogen and phosphate in aquatic habitats can trigger explosive algal blooms that consume the oxygen dissolved in water. 13 Threats to biodiversity Acid precipitation: oxides of sulphur released in the atmosphere (from fossil fuels) react with water to form sulphuric acid. Acid rain decrease the pH of many lakes, affecting fish populations. Biomagnification: the increase across trophic levels in the concentration of a toxic substance inside tissues of organisms. Biomagnification in a specific trophic level is caused by the very large biomass ingested from the lower trophic level below. Ex: PCBs (polychlorinated biphenyls) Ex: Pharmaceuticals and steroids 14 Threats to biodiversity Global warming: the emission of CO2 and other greenhouse gases causes the solar radiation to reflect back onto the Earth’s surface and increase the average global temperature. Species unable to disperse, adapt or with low genetic variation are at higher risk. 15  Topic 16 Conservation biology 16.3 – Biodiversity and conservation status 3 levels of biodiversity Genetic diversity: diversity within and between populations. A decrease in genetic diversity (extinction of a population) can prevent microevolution and limit the adaptive potential of a species. Species diversity: variety of species within an ecosystem or across the biosphere. The loss of a species can be local (= extirpation) or global (in all ecosystems = extinction). Ecosystem diversity: variety of ecosystems. The altering of ecosystems can cause species loss, loss of ecological functions, decline in distribution, disruption of biotic processes and species interactions. 3 status categories: collapsed, critically endangered and endangered. Human activities are altering trophic structures, energy flow, chemical cycling, natural disturbance and ecosystems processes. Threats to biodiversity include habitat loss, climate change, invasive species, overharvesting, pollution… 17 Why protect biodiversity? The human population relies on biodiversity and natural resources. Wild species are used for food, fuel, and fiber, medicines, building materials, spices, and decorative items. The natural functioning of biological communities provides valuable services to humans (water purification, pollution breakdown, formation, maintenance of soils and flood control, pollination of crops, climate regulation, recovery from natural disasters). These ecosystem functions depend on the integrity of natural communities and ecosystems. Strong emotional, cultural and spiritual connections with nature. Biodiversity can be seen as a rich genetic heritage from a complex evolutionary history (moral obligation). Species entitled to life. 18 Biodiversity hot spots Biodiversity hot spots: are relatively small areas containing many endemic species (found nowhere else in the world) and a large number of endangered species. 33% of plants, amphibians, reptiles, birds and mammals species are found in 1.5% of the Earth’s land area. 30% of bird species are found in 2% of the Earth’s land area. 17% of plant species are found in 0.5% of the Earth’s land area. Protecting these hot spots is the priority of many conservation strategies. However, those hotspots are often specific to certain taxonomic groups and ignore many invertebrates and microorganisms species. 19 Conservation biology Conservation biology: The integrated study of ecology, evolutionary biology, physiology, molecular biology, and genetics to sustain biological diversity of all levels. Despite extinction have occurred for billions of years, the current loss in biodiversity is due to a high rate of extinction of all known extant species. Not all species are assessed. WWF report (2018): diversity in mammals, birds, fish, reptiles, and amphibians have decreased: 68% of 32,000 populations were lost between 1970 and 2020! ~50% of species are predicted to go extinct before 2100! www.iucnredlist.org 20 Some conservation initiatives Captive-breeding program to breed endangered species in zoos in order to build a healthy and genetically diverse population before reintroducing them back into the wild. International Potato Center (CIP). Research-development organization with a focus on potato, sweetpotato, Andean roots and tubers to enhance access to affordable nutritious food in developing countries.  Leverages diversity (4,000 native potato varieties) and combines genomics, breeding programs, selection for climate resilient varieties, education and training for a sustainable agriculture. 21 Some conservation initiatives 39 Canadian National parks covering 3.3% of land area Aims at protecting the Canada’s ecological integrity: - presence of species that are expected in the region - maintenance of ecological processes that are expected in the region. 22 Habitat conservation We now see a shift in conservation strategies from the protection of species to the protection of entire ecosystem communities Fragmentation of forests has a greater impact on species diversity, with many species adapted to forest interior declining when patches are the smallest. Corridors that connect patches can help protect some of the biodiversity by allowing large mammals to cross human-made obstacles and promoting dispersal. The establishment of large protected Nature Reserves are key to the maintenance of ecosystem communities and their biodiversity. 23 Habitat conservation Ex: Costa Rica. Establishment of zoned reserves: with protected areas (undisturbed by human activities) surrounded by areas with limited and regulated human activities. 24 “No intervention” policy in national parks Disturbances such as floods or fires are often considered to be natural and are allowed to play out on their own. Management policies. Many species do depend on periodic fires to germinate or thrive (ecological successions). 25 “No intervention” policy in national parks Ex: 1988 fires in the Yellowstone Park were not supressed and 36% of the park area was burned. Recovery from many species was immediate and biodiversity increased since. - Cones of lodgepole pines open at extreme temperatures. - Aspen seedlings germinate faster on bare mineral soil. - Rodents repopulated quickly the burned areas. - New feeding opportunities for many grazers and birds Lodgepole pines (Pinus contorta ) 26 Conservation status The IUCN (International Union for Conservation of Nature) assesses the global conservation status of species and maintains a Red List of Threatened Species. A large fraction of species in all most taxa (>150 species) are threatened (vulnerable + endangered + critically endangered) % of threatened species 1.5% 6% 7.5% 14% 26% 28% 33% 34% 34% 37% 38.5% 41% 63% 27 Conservation status COSEWIC (Committee on the Status of Endangered Wildlife in Canada) Extirpated Special Not at Extinct (Canada) Endangered Threatened Concern risk Assesses the conservation status of species found in Canada and makes recommendations to the federal government on which species needs a protected status. Criteria include declining abundance, limited distribution, small population size (quantitative) and information on threats, life history traits (qualitative). Conservation agencies need to coordinate research and management efforts for species whose distribution overlaps national borders. 28 Conservation status Ex: Whooping crane (Grus americana). Migrate north from wintering grounds (USA) to breed in boreal wetlands (Canada) Hunting, egg collection and habitat degradation caused the decline in population size (10,000  22 birds). Their migration corridor is From the Minister of Public undergoing continuous industrial development. Works and Government Services Canada in cooperation with the U.S. Department of the Interior, Fish and Wildlife Service Late 1940s, government agencies in Canada and the United States began actively sharing data and expertise to prevent the extinction of the whooping crane (breeding programs, reintroduction, aerial survey and monitoring…) 29 Conservation status Conservation status assessment are performed every year by COSEWIC. Extirpated Special Not at Changes in status since 1977 vary depending on the initial status: Extinct (Canada) Endangered Threatened Concern risk Species initially classified as “Not at risk”, “Endangered”, or “Extirpated” tend to remain at their initial status. Species initially classified as “Special concern” or “Threatened” saw their status deteriorate Red bars indicate apparent recoveries due to increased sampling efforts. Favaro et al 2014 30