CAMPBELL BIOLOGY IN FOCUS Overview: Communities in Motion Urry Cain Wasserman Minorsky Jackson Reece Pearson Education, Inc.

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1 CAMPBELL BIOLOGY IN FOCUS Overview: Communities in Motion Urry Cain Wasserman Minorsky Jackson Reece 41 A biological community = ex: carrier crab : Species Interactions Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge Concept 41.1: Interactions within a community may help, harm, or have no effect on the species involved interspecific interactions Ex: competition (-,-) predation (+,-) herbivory (+,-) symbiosis parasitism (+,-) mutualism (+,+0 commensalism (+,0) facilitation Competition Interspecific competition = competitive exclusion =

2 Ecological Niches and Natural Selection Figure 41.2 A. distichus perches on fence posts and other sunny surfaces. A. insolitus usually perches on shady branches. Evolution is evident in the concept of the ecological niche (def = ) Ecologically similar species can coexist if: A. ricordii A. insolitus A. aliniger A. distichus A. christophei A. cybotes A. etheridgei Experiment Chthamalus High tide Fundamental vs Realized Niche Ocean Balanus Balanus realized niche Chthamalus realized niche Low tide A species fundamental niche = A species realized niche = As a result of competition, a species fundamental niche may differ from its realized niche Results High tide Chthamalus fundamental niche Ocean Low tide

3 Figure 41.4 Percentages of individuals in each size class G. fuliginosa Los Hermanos Daphne G. fortis Santa María, San Cristóbal Beak depth G. fuliginosa, allopatric G. fortis, allopatric Sympatric populations Beak depth (mm) Facilitation Facilitation (+/+ or 0/+) is an interaction in which one species has positive effects on another species without direct and intimate contact For example, the black rush makes the soil more hospitable for other plant species Figure 41.9 Concept 41.2: Diversity and trophic structure characterize biological communities Number of plant species Two fundamental features of community structure are species diversity and feeding relationships Sometimes a few species in a community exert strong control on that community s structure (a) Salt marsh with Juncus (foreground) (b) 0 With Juncus Without Juncus

4 Species Diversity Species diversity of a community is the variety of organisms that make up the community It has two components: species richness and relative abundance Species richness is the number of different species in the community Relative abundance is the proportion each species represents of all individuals in the community Figure Two communities can have the same species richness but a different relative abundance A B C Community 1 A: 25% B: 25% C: 25% D: 25% D Community 2 A: 80% B: 5% C: 5% D: 10% Figure Communities with higher diversity are More productive and more stable in their productivity Able to produce biomass (the total mass of all individuals in a population) more consistently than single species plots Better able to withstand and recover from environmental stresses More resistant to invasive species, organisms that become established outside their native range Quaternary consumers: carnivores Tertiary consumers: carnivores Secondary consumers: carnivores Primary consumers: herbivores and zooplankton Primary producers: plants and phytoplankton

5 Trophic Structure Trophic structure is the feeding relationships between organisms in a community Food chains link trophic levels from producers to top carnivores A food web is a branching food chain with complex trophic interactions Species may play a role at more than one trophic level Baleen whales Crabeater seals Humans Smaller toothed whales Leopard seals Sperm whales Elephant seals Birds Fishes Squids Carnivorous plankton Krill Copepods Phytoplankton Species with a Large Impact Species with a Large Impact Certain species have a very large impact on community structure Such species are highly abundant or play a pivotal role in community dynamics Dominant species are those that are most abundant or have the highest biomass Why? Keystone species exert strong control on a community by their ecological roles, or niches ex: sea stars

6 Figure Experiment Number of species present Results With Pisaster (control) Without Pisaster (experimental) scientists-find-out-whats-killing-westcoast-starf/ Year Species with a Large Impact Ecosystem engineers (or foundation species ) = For example, beaver dams Concept 41.3: Disturbance influences species diversity and composition Characterizing Disturbance Fire is a significant disturbance in most terrestrial ecosystems, esp. PNW A high level of disturbance is the result of a high intensity and high frequency of disturbance Low disturbance levels result from either low intensity or low frequency of disturbance

7 The intermediate disturbance hypothesis suggests that moderate levels of disturbance can foster the greater diversity Number of taxa Ecological Succession Ecological succession is the sequence of community and ecosystem changes after a disturbance Primary succession occurs where no soil exists when succession begins Secondary succession begins in an area where soil remains after a disturbance Index of disturbance intensity (log scale) Ecological Succession Figure Retreating glaciers provide a valuable field research opportunity for observing succession Succession on the moraines in Glacier Bay, Alaska, follows a predictable pattern of change in vegetation and soil characteristics 1. The exposed moraine is colonized by pioneering plants, including liverworts, mosses, fireweed, Dryas, and willows Alaska Glacier Bay Kilometers

8 Figure Figure Pioneer stage 1 Pioneer stage 2 Dryas stage Glacier Bay Glacier Bay Alaska Alaska Kilometers Kilometers Figure Figure Pioneer stage 1860 Glacier Bay Dryas stage 1 Pioneer stage Alaska 1860 Glacier Bay 2 Dryas stage Alaska Kilometers 3 Alder stage 4 Spruce stage Kilometers 3 Alder stage

9 Ecological Succession Human Disturbance Succession is the result of changes induced by the vegetation itself vegetation increases soil nitrogen content (name this interspecific interaction?) Humans have the greatest impact on biological communities worldwide Human disturbance to communities usually reduces species diversity Trawling is a major human disturbance in marine ecosystems Figure Human Disturbance: trawling The area disturbed by bottom trawling commercial fishing fleets exceeds the combined physical footprint of other major human activities considered.

10 Figure 41.UN03 Two-species interactions are classified by the impact each species has on the other. Thus, a competitive interaction is one where the populations of each species are hurt by the presence of the other species, usually because each species uses the same resources. Niche partitioning enables species to coexist by A. avoiding direct competition. B. encouraging mutualistic interactions. C. enabling prey to hide from predators. D. creating new resources. E. allowing abiotic factors, such as climate or nutrient availability, to influence the community. What is one difference between the fundamental niche and the realized niche? This graph shows the effect of soil ph on microbial diversity. One conclusion you should draw from this figure is A. The realized niche is larger. B. The fundamental niche is determined by competitors C. The realized niche is determined by abiotic resources. D. Individuals will be found only in the realized niche. E. The difference is called the occupied niche. A. the higher the soil ph, the higher the microbial diversity. B. the lower the soil ph, the higher the microbial diversity. C. microbes eat ph. D. the scientists couldn t find any acidic or basic soils. E. there appears to be an optimal ph value for maximizing microbial diversity.

11 Look at the following figure, which shows a partial Chesapeake Bay food web. If sea nettles disappeared, A. there would be fewer fish eggs. B. there would be more striped bass. C. there would be fewer zooplankton. D. striped bass would have less food to eat. E. sea nettles would reinvade from the ocean.