Chapter 17: Species Interactions and Community Structure PDF

Chapter 17 Species Interactions and Community Structure © 2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education. ...

Chapter 17 Species Interactions and Community Structure © 2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  Outline Concept 17.1 A food web summarizes the feeding relations in a community. Concept 17.2 Indirect interactions between species are fundamental to communities. Concept 17.3 The feeding activities of a few keystone species may control the structure of communities. Concept 17.4 Mutualists can act as keystone species. © 2019 McGraw-Hill Education.  Introduction Feeding relationships are easily documented interactions in communities. Early approach to study of communities was to describe who eat whom. These feeding relationships are called food webs. © 2019 McGraw-Hill Education. © 2019 McGraw-Hill Education.  17.1 Community Webs Earliest work on food webs concentrated on simplified communities. Even in “impoverished faunas” feeding relations are complex. More manageable to study than food webs of diverse communities. © 2019 McGraw-Hill Education.  Detailed Food Webs Reveal Great Complexity Winemiller described feeding relations among tropical freshwater fish at 2 sites. Represented food webs in various ways. Webs that only included common species. Webs that excluded weakest trophic links. Both produced complex food webs. Most comprehensible focused on the strongest trophic links. © 2019 McGraw-Hill Education. © 2019 McGraw-Hill Education.  Strong Interactions and Food Web Structure Paine suggested feeding activities of a few species may have a dominant influence on community structure - strong interactions. Criterion for strong interaction is degree of influence on community structure. Recognizing interaction strength can affect depiction of food web. © 2019 McGraw-Hill Education.  Phragmites Food Web Tscharntke studied food webs associated with wetland reeds (Phragmites australis). Reeds attacked by fly, Giraudiella inclusa. Fly attacked by 14 parasitoid wasp species. Predator specializes on eating fly larvae and consequently on parasitoid wasps. Distinguished between weak and strong interactions in food web. Allows determination of species with most significant influences. © 2019 McGraw-Hill Education.  Click to edit Master title style © 2019 McGraw-Hill Education.  17.2 Indirect Interactions Direct interactions (competition, predation, etc.) between two species do not involve intermediary species. Indirect interactions are the effects of one species on another through a third species. Trophic cascades, indirect commensalism, apparent competition. © 2019 McGraw-Hill Education.  Indirect Commensalism One species indirectly benefits another species (through a third species) while it is neither helped or harmed. Beavers fell cottonwood trees which then produce stump sprouts. Herbivorous beetles (Chrysomela confluens) prefer consuming high nutrition sprout leaves. Beetles grow larger, faster and utilize defensive compounds found in leaves. Beavers have positive effect on beetles through cottonwood trees. © 2019 McGraw-Hill Education.  Beavers, Beetles, and Cottonwood Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide © 2019 McGraw-Hill Education.  Apparent Competition Negative effects between two competitors who share a predator or herbivore, or. One species may facilitate populations of predator of a second species. Orrock et al. studied apparent competition between Brassica nigra (exotic) and Nassella pulchra (native). Brassica shelters mammals which feed on surrounding vegetation. Increased herbivory on Nassella. © 2019 McGraw-Hill Education.  Brassica and Nassella Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide © 2019 McGraw-Hill Education.  17.3 Keystone Species Feeding activities of a few species, keystone species, have inordinate influences on community structure. If keystone species reduce likelihood of competitive exclusion, their activities increase number of species that can coexist in communities. Some predators can increase species diversity. © 2019 McGraw-Hill Education.  Food Web Structure and Species Diversity Paine found as number of species in intertidal food webs increased, proportion of the web represented by predators also increased. Higher proportion of predators produces higher predation pressure on prey populations, in turn promoting higher diversity. © 2019 McGraw-Hill Education.  Experimental Removal of Sea Stars Paine removed top predator, Pisaster, from intertidal food web. Over 2 years of monitoring. Diversity of control plot remained at 15. Diversity of removal plot dropped to 8. After Pisaster removal, plot was dominated by mussels and gooseneck barnacles. Pisaster is keystone species; without it the community collapsed. © 2019 McGraw-Hill Education.  Removing Sea Stars from Food Webs Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide © 2019 McGraw-Hill Education.  Snail Effects on Algal Diversity To study influence of intertidal snails on diversity of intertidal algae need to know. Herbivore food preference. Competitive relationships between plant species in the local community. Variance in feeding preferences and competitive relationships across environments. © 2019 McGraw-Hill Education.  Study of Littorina littorea Lubchenco studied (Littorina littorea). Snails preferred small, ephemeral, tender algae (Enteromorpha spp.), not tough perennial species (such as Chondrus). Tidepools with high densities of Enteromorpha had low snail density; pools with high densities of Chondrus had high snail density. Without Littorina, Chondrus is competitively displaced. © 2019 McGraw-Hill Education.  Effects of Littorina on Algal Communities Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide © 2019 McGraw-Hill Education.  Snails and Crabs When snails are present in high densities, Littorina grazes down Enteromorpha, releasing Chondrus from competition. Green crabs (Carcinus maenus) prey on young snails, preventing juveniles from colonizing tide pools. Populations of Carcinus are controlled by seagulls. © 2019 McGraw-Hill Education.  Variations in Snail Density Low snail density - Enteromorpha dominates tide pool. Medium snail density - competitive exclusion eliminated, and algal diversity increased. High snail density – feeding requirements are high enough that snails eat preferred algae and less-preferred algae. Algal diversity decreased. © 2019 McGraw-Hill Education.  Fish as River Keystone Species Power investigated whether California roach and steelhead trout significantly influence food web structure. Found that predatory fish decrease algal densities. Low predator density increased midge production. Increased midge feeding pressure on algal populations. Thus, fish act as keystone species. © 2019 McGraw-Hill Education.  Eel River Food Web Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide © 2019 McGraw-Hill Education.  17.4 Mutualistic Keystones Mutualists can act as keystone species. Keystone species have high impact on community structure, despite low biomass. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide © 2019 McGraw-Hill Education.  A Cleaner Fish as a Keystone Species Many fish species on coral reefs clean ectoparasites from other fish (mutualism). Cleaner wrasse can remove and eat 1,200 parasites per day. When wrasses disappear (or are removed) 24% median reduction in fish species diversity. When wrasses appear (or are added), 24% median increase in fish species diversity. Cleaner wrasse is keystone species on Red Sea coral reefs. © 2019 McGraw-Hill Education.  Seed Dispersal Mutualists as Keystone Species Christian observed native ants disperse 30% of shrubland seeds in fynbos of South Africa. Seed-dispersing ants bury seeds in sites safe from predators and fire. Argentine ants have displaced many native ant species that disperse large seeds. Substantial reductions in seedling recruitment by plants producing large seeds. © 2019 McGraw-Hill Education.  Argentine Ants and Seedlings Copyright © McGraw-Hill Education. Permission required for reproduction or display. Access the long description slide © 2019 McGraw-Hill Education.  Review Introduction. Community Webs. Indirect Interactions. Keystone Species. Mutualistic Keystones. © 2019 McGraw-Hill Education.