Species Interactions PDF

Species interactions Health form due today No form = no trip! BYO handouts  Outline Community ecology Niche space Species interactions Energy flow and food webs Keystone species Using species interactions for biocontrol Community ecology Understanding the interactions betwee...

Species interactions Health form due today No form = no trip! BYO handouts  Outline Community ecology Niche space Species interactions Energy flow and food webs Keystone species Using species interactions for biocontrol Community ecology Understanding the interactions between and within populations and environment Predation, competition for resources, cooperation Structure of communities – food webs Human impacts on communities and their interactions Trophic ‘Pyramid’ Animal Ecology, Charles Elton, 1927 introduces the ‘Pyramid of numbers’ – number, weight or energy of individuals in each trophic level Trophic level – position of an organism in a food web Also introduces the idea of ecological niche in terms of functional roles and what organisms eat The beginning of a movement to © 2012 Nature Education understand how species interact Where a species lives is determined by its niche Niche – biotic and abiotic conditions required for a species to exist and the role a species plays in an ecosystem n-dimensional hypervolume Fundamental niche – possible env. a species could occupy Realized niche – actual env. a species lives in due to species interactions Trophic ‘Pyramid’ Lindemann, 1942 “The tropic-dynamic aspect of ecology” Incorporated energy transfer using the Cedar Bog Lake as a model system – both biotic and abiotic Described pathways of energy flow and nutrient cycling Related energy flow and ecosystem structure to ecosystem function Note ‘Rule of ten’ Types of ‘Pyramids’ Primary producers tend to have higher biomass, energy and abundance Depending on the study system and the type of pyramid, the size of each trophic level can be quite different. From Trophic ‘Pyramid’ to community food-web ’ Jacomina Heymans et al 2014 PLoS One From Trophic ‘Pyramid’ to community food-web ’ Producers Jacomina Heymans et al 2014 PLoS One From Trophic ‘Pyramid’ to community food-web 1° Consumers herbivores ’ Jacomina Heymans et al 2014 PLoS One From Trophic ‘Pyramid’ to community food-web 2° Consumers predators ’ Jacomina Heymans et al 2014 PLoS One Species interactions Can be negative, positive or neither (+/-) In some interactions both species are damaged or use energy (-/-) Predation and herbivory (+/-0) Broad definition: one species benefits, one is disadvantaged Predator usually kills prey Herbivory doesn’t necessarily result in killing the plant, but reduce its fitness (growth, fecundity) Predator or herbivore preferences – proportion of prey in the diet of a predator vs proportion in the environment (optimal foraging strategy) As you go further up the food web, species become more generalist, and eat other species from a wider range of habitats Baskerville et al 2011 PLoS Comput Biol Parasitism (+/-) Parasite consumes all or part of host Different to predation because the host doesn’t necessarily die E.g. malaria, parasitic wasps, lice, leeches, mistletoe Competition (-/-) (interspecific) Each species affected negatively When individuals of once species suffer a reduction in fitness from a second species due to their shared use of limiting resources Exploitation competition of shared resources or interference competition by restricting access Both biotic and abiotic resources  Competitive exclusion Niche – biotic and abiotic conditions required for a species to exist and the role a species plays in an ecosystem Some species will be better at exploiting resources than others – competitive exclusion Therefore, no two species will occupy the exact same niche in the same location – resource partitioning But! The paradox of the plankton…  Mutualism (+/+) Reciprocally positive interaction between species Many examples! Seed dispersal, pollination Even your own mitochondria?! Can you name some other ones? Facilitation - commensalism Any interaction in which at least one species benefits – generally in close proximity “An interaction in which the presence of one species alters the environment in a way that enhances growth, survival, or reproduction of a second, neighboring species” Bronstein 2009 e.g. nitrogen fixing plants that benefit surrounding plants (Zele et al 2018)  Commensalism (+/0) one species benefits One species benefits, one unaffected E.g. coral, trees, providing structural habitat for other species but no benefit Ecosystem engineers Termites - ecosystem engineers Up to 10 000 individuals per square meter Important for: Decomposition Retaining soil moisture (sheeting) Soil nutrient heterogeneity Think of some other ‘ecosystem engineers’ Why are food webs shaped the way they are? Depends on many interacting factors across time and space Biogeographic history Climate and microclimate Host plant range Environmental stability Population dynamics and survival processes From species interactions to food webs Essentially “Which species eat other species” A network indicating TROPHIC relationships among species within a community The sets of species which interact to maintain dynamic and sustainable ecosystems We often understand little of these interactions and how species loss can disrupt whole-ecosystem stability Keystone species First described by Robert Payne in 1966, who experimentally removed sea stars from a rocky shore Sea star at the top of the food chain Mussels became dominant as no sea stars were eating them Diversity of other groups declined Sea otters are also keystone species because they control urchin populations, allowing kelp to grow  Keystone Species Are species that plays an important role in an ecosystem Shape the function and diversity of the rest of the ecosystem E.g. Otters maintain kelp ecosystems by eating sea urchins Trophic cascades – when one part of the food web is suppressed, influencing other parts Biocontrol: applying species interactions to ecological problem Use of on species to reduce a pest species Agricultural and natural ecosystems Releasing large numbers into a habitat – often predators, pathogens, parasites Importing enemies of pest or invasive species Or increasing effectiveness of native enemies Biocontrol agent can either be short or long term Biocontrol methods Find a range of potential natural enemies and evaluate their potential effects Carry out small-scale experimental controlled releases Monitor through time Scale-up releases Introduced species can adapt, disperse, change host preference – need to monitor carefully (which often is not done)  Success stories Prickly pear was introduced to Australia in 1831 and became invasive Cactoblastis Moth (Cactoblastis cactorum) was introduced to parts of north-east Australia to reduce Prickly Pear (Opuntia stricta) The moth rapidly destroyed the infestations Things can go very wrong Cane toad in Australia Introduced to kill sugar cane pest beetles Ecological disaster Out-compete and predate on species that are native and not adapted to their presence Didn’t reduce beetles anyway! How do you control species interactions? Many more examples of ecological disasters and success stories References Simberloff, Daniel, and Peter Stiling. "How risky is biological control?." Ecology 77.7 (1996): 1965- 1974. Bronstein, J.L. (2009), The evolution of facilitation and mutualism. Journal of Ecology, 97: 116 Insect photos: www.alexwild.com