Presentation on theme: "1 Chapter 3: Species Populations, Interactions and Communities Principles of Environmental Science - Inquiry and Application by William and Mary Ann Cunningham."— Presentation transcript:
3 Chapter 3 - Topics Who Lives Where, and Why? Species Interactions Population Dynamics Community Properties Communities in Transition
11 Part 1: Who Lives Where, and Why? Generalists vs. Specialists
12 Tolerance Limits Each environmental factor (temperature, nutrient supply, etc.) has both minimum and maximum levels beyond which a species cannot survive or is unable to reproduce.
13 Abundance and Distribution of Species Liebig - proposed that the single environmental factor in shortest supply relative to demand is the critical determinant in species distribution Shelford - added to Liebig's work by proposing that the single environmental factor closest to tolerance limits determines where a particular organism can live
14 Today we know that for many species the interaction of several factors, rather than a single limiting factor, determines biogeographical distribution. Sometimes, the requirements and tolerances of species are useful indicators of specific environmental characteristics.
15 Adaptation and Natural Selection Two types of adaptation: Acclimation - changes in an individual organism due to non-permanent physiological modifications Evolution - gradual changes in a species due to changes in genetic material and competition Theory of evolution - developed by Charles Darwin and Alfred Wallace.
16 Natural selection - genetic combinations best adapted for present environmental conditions tend to become abundant Spontaneous, random mutations Selective pressure - physiological stress, predation, competition, luck
18 Types of speciation Allopatric: due to geographic isolation Sympatric: due to genetic make up differences. Isolation could result in the change of physical, behavioral and genetic characteristics of individuals. Based on how it affects populations, environmental pressures could be directional, stabilizing or disruptive.
19 The Taxonomic Naming System ADD TABLE 3.1
20 Habitat - the place or set of environmental conditions in which a particular organism lives Ecological niche - the role played by a species in a biological community The Ecological Niche
21 Resource Partitioning Over time, niches can evolve as species develop new strategies to exploit resources. Law of Competitive Exclusion: No two species will occupy the same niche and compete for the same resources in the same habitat for very long.
23 Part 2: Species Interactions Most obvious are Predation and Competition - antagonistic relationships
24 How does competition shape population Intraspecific: Among organisms of the same spp. Dispersal, Territoriality and Generational resource partitioning. Interspecific: different spp. Resource partitioning NB. When two species compete, the one in the center of its tolerance limit has the advantage.
25 How does predation affect spp populations in communities Adjustments in behavior and body characteristics of predators and prey
26 Defensive Mechanisms
28 Batesian Mimicry
29 Keystone species - species that play essential community roles (examples: mycorrhizae, giant kelp)
30 Three Types of Symbiosis: Commensalism - one member benefits, while the other is neither benefited nor harmed Mutualism - both members of the partnership benefit; Parasitism - a form of predation where one species benefits and the other is harmed ADD FIG A-C
31 Part 3: Population Dynamics Exponential growth - the unrestricted increase in a population (also called the biotic potential of a population) Carrying capacity - the maximum number of individuals of any species that can be supported by a particular ecosystem on a sustainable basis
32 Two types of populations r-selected: grow exponentially, expend energy in giving birth to progeny. k-selected: grow logistically, expend energy raising progeny
33 Overshoots and Diebacks ADD FIG. 3.20
34 Growth to a Stable Population ADD FIG. 3.22
35 Environmental Resistance Environmental resistance - factors that tend to reduce population growth rates: Density-dependent - linked to population size - disease, lack of food Density-independent - often environmental - droughts, floods, habitat destruction Intrinsic - attributes of a species - slow reproduction Extrinsic - external to a species - predators, competitors, environmental risks
36 Reproductive Strategies r-Selected spp Short life Rapid growth Early maturity Many, small offspring Little parental care and protection Little investment in individual offspring Adapted to unstable environment Colonizers Niche generalists Prey Regulated mainly by intrinsic factors Low trophic level k-Selected spp Long life Slower growth Late maturity Few, large offspring High parental care and protection High investment in individual offspring Adapted to stable environment Later stage of succession Niche specialists Predators Regulated mainly by extrinsic factors High trophic level
37 Part 4: Community Properties Primary productivity - a community's rate of biomass production, or the conversion of solar energy into chemical energy stored in living (or once-living organisms) Net primary productivity - primary productivity minus the energy lost in respiration Productivity depends on light levels, temperature, moisture, and nutrient availability.
38 Relative biomass accumulation of major world ecosystems. ADD FIG. 3.29
39 Abundance and Diversity Abundance - the number of individuals of a species in an area Diversity - the number of different species in an area A useful measure of the variety of ecological niches or genetic variation in a community Decreases as we go from the equator towards the poles Abundance and diversity depend on total resource availability in an ecosystem.
40 Antarctic Marine Food Web Complexity - the number of species at each trophic level and the number of trophic levels in a community
41 Stability and Resilience Stability - a dynamic equilibrium among the physical and biological factors in an ecosystem or a community Resiliency - the ability to recover from disturbance Three kinds of stability or resiliency in ecosystems: Constancy - lack of fluctuations in composition or functions Inertia - resistance to perturbations Renewal - ability to repair damage after disturbance
42 Community structure Distribution of members of a population in a given space can be: Random - individuals live wherever resources are available Ordered - often the result of biological competition Clustered - individuals of a species cluster together for protection, mutual assistance, reproduction, or to gain access to a particular environmental resource ADD FIG A-C
43 Edges and Boundaries Ecotones- the boundaries between adjacent habitats Often rich in species diversity Example: the boundary between a forest and a meadow
44 Edge effects - the environmental and biotic conditions at the edge of a habitat Temperature, moisture levels, predator species, etc. Edge effects associated with habitat fragmentation are generally detrimental to species diversity. Core habitat - the interior area of a habitat Habitat not impacted by edge effects Some species avoid edges and ecotones and prefer interior environments. Edge vs. Core
45 Part 5: Communities in Transition Ecological succession - the process by which organisms occupy a site and gradually change environmental conditions by creating soil, shelter, shade, or increasing humidity Primary succession - occurs when a community begins to develop on a site previously unoccupied by living organisms Secondary succession - occurs when an existing community is disrupted and a new one subsequently develops at the site
46 Primary Succession on Land
47 Exotic Species Sometimes communities can be completely altered by the introduction of exotic species. Exotic species are often introduced by humans. Successful exotics tend to be prolific, opportunistic species, such as goats, cats, and pigs. Many ecologists consider exotic species invasions the most pressing hazard for biological communities in the coming century.