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Chapter 5 Biodiversity, Species Interactions and Population Control Species Interact in major ways Interspecific competition – 2 or more species interact to gain access to limited resources Predation – prey/predator parasitism - parasite/host Mutualism – benefits both species Commensalism – benefits one species , no effect on the other Cyclic changes – sharp increases in number followed by seemingly periodic crashes Wolves controlling deer and moose populations Sheep and rabbits controlling plant growth Role of predation Competition for resources the greater the overlap the more intense the competition Resource partitioning –specialized traits allow species to use shared resources at different times Competitive exclusion – intense copetition between 2 equal species, both suffer (one more than the other) by having reduced access to resources Population Dynamics characteristics of populations change in response to environmental conditions Size – number of individuals Density – number of individuals in a certain space Distribution – spatial pattern – clumping,uniform dispersion, random dispersion Age distribution structure - percentage of individuals in each age group uniform Clumping random What limits population growth? Birth, death, immigration, emigration Population change = (birth+ immigration) - (death + emigration) dependent on resource availability or other environmental changes Intrinsic rate of increase® rate at which a population could grow if it has unlimited resources always limits - light, water, space, nutrients “High r” – reproduce early in life, short generation ie. reproduce many times many offspring: house fly Carrying capacity - capacity for growth number of individuals of a given species that can be sustained indefinitely in a given area (K) determined by interaction between biotic potential and environmental resistance (factors that act jointly to limit a population) Population Dynamics and Carrying Capacity Basic Concept: Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths) – There is a dynamic balance between biotic potential and environmental resistance Carrying Capacity (K) Exponential curve is not realistic due to carrying capacity of area Carrying capacity is maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability) Biotic Potential Ability of populations of a given species to increase in size – Abiotic Contributing Factors: Favorable light Favorable Temperatures Favorable chemical environment - nutrients – Biotic Contributing Factors: Reproductive rate Generalized niche Ability to migrate or disperse Adequate defense mechanisms Ability to cope with adverse conditions Environmental Resistance Ability of populations of a given species to increase in size – Abiotic Contributing Factors: Unfavorable light Unfavorable Temperatures Unfavorable chemical environment - nutrients – Biotic Contributing Factors: Low reproductive rate Specialized niche Inability to migrate or disperse Inadequate defense mechanisms Inability to cope with adverse conditions Population Density Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area – Some species exist in high densities - Mice – Some species exist in low densities - Mountain lions Density depends upon – social/population structure – mating relationships – time of year Reproductive Strategies Goal of every species is to produce as many offspring as possible Each individual has a limited amount of energy to put towards life and reproduction This leads to a trade-off of long life or high reproductive rate Natural Selection has lead to two strategies for species: r - strategists and K - strategists r - Strategists Spend most of their time in exponential growth K Maximize reproductive life Minimum life R Strategists Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate – (r) Population size fluctuates wildly above and below carrying capacity – (K) Generalist niche Low ability to compete Early successional species K - Strategists Maintain population at carrying capacity (K) Maximize lifespan K K- Strategist Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species Survivorship Curves Late Loss: K-strategists that produce few young and care for them until they reach reproductive age thus reducing juvenile mortality Constant Loss: typically intermediate reproductive strategies with fairly constant mortality throughout all age classes Early Loss: r-strategists with many offspring, high infant mortality and high survivorship once a certain size and age Survivorship curves proportion of survivors of a particular species in a particular age group a)late loss – type I - elephant b) early loss – type II songbirds c) constant loss - intermediate reproductive strategies- starfish J-shaped exponential growth curve, growth starts slowly then speeds up S - shaped curvelogistic growth curve - slow start, rapid exponential growth, levels off when K is reached Population growth Population cycles in nature relatively stable - slight fluctuation above and below carrying capacity, tropical rain forest erupt - high peak, crash - raccoons cyclic - “boom” and “bust” Effect of population density on population growth? Density Independent – floods, drought, hurricane, habitat destruction, pesticide spraying Density dependent – competition for resources, predation, disease – infectious diseases – plague in Europe Communities and ecosystems respond to environmental change Primary succession- gradual establishment of biotic communities in life less areas where there is no soil in a terrestrial ecosystem or nobottom sediment in an aquatic ecosystem Secondary succession –series of comunities or ecosystems with different species develop in places containing soil or bottom sediment Primary succession bare rock subject to weathering crumbles into particles, releasing nutrients Pioneer or early successional species (lichens or mosses)attach to rock and start the process of rock formation by secreting mild acids Mid successional plants – grasses, herbs, small plants Late successional species trees that can tolerate shade Secondary succession ecosystem has been disturbed , removed or destroyed, some soil or bottom sediment remains abandoned farmland, burned or cut forests,heavily polluted streams, flooded lands Living systems are sustained through constant change complex system of positive and negative feedback loops that interact to provide stability Inertia or persistence – ability of a living system such as grassland or forest to survive moderate disturbances Resilence – ability of a living system to be restored through secondary succession after a moderate disturbance Conservation Biology Investigate human impacts on biodiversity Develop practical approaches to maintaining biodiversity endangered species management, wildlife reserves, ecological restoration, environmental ethics Prevent premature extinction how ? Status of natural populations, species in danger of extinction Status of the functioning of ecosystems Measures taken to maintain habitat quality which will support wild species population Understand status of natural populations Measure current population size Determine how size will change with time Determine whether populations are sustainable Anthropogenic impact Fragmenting or degrading habitat, simplifying natural ecosystems, strengthening genetic resistance to pesticides, eliminating predators, introduce alien species, over harvesting, interfering with nutrient cycles Working with Nature Learn six features of living systems – Interdependence – Diversity – Resilience – Adaptability – Unpredictability – Limits Basic Ecological Lessons 1. 2. 3. 4. Sunlight is primary source of energy Nutrients are replenished and wastes are disposed of by recycling materials Soil, water, air, plants and animals are renewed through natural processes Energy is always required to produce or maintain an energy flow or to recycle chemicals Basic Ecological Lessons 5. 6. 7. 8. Biodiversity takes many forms because it has evolved over billions of years under different conditions Complex networks of + and – feedback loops exist Population size and growth rate are controlled by interactions with other species and with abiotic Organisms generally only use what they need Four Principles for Sustainable 1. 2. 3. We are part of, not apart from, the earth’s dynamic web of life. Our lives, lifestyles, and economies are totally dependent on the sun and the earth. We can never do merely one thing (first law of human ecology – Garret Hardin). 4. Everything is connected to everything else; we are all in it together.