Community ecology Ecosystems Ch 54 55 Lecture Objectives
Community ecology + Ecosystems Ch. 54 & 55 Lecture Objectives 1. Concept of a Niche 2. Interspecific Species Interactions 3. Ecosystem Ecology (Trophic structures, energy pyramids, keystone species)
Communities in Motion A biological community is an assemblage of populations of various species living close enough for potential interaction
Ecological Niches and Natural Selection The sum of a species’ use of biotic and abiotic resources is called the species’ ecological niche Ecologically similar species can coexist in a community if there are one or more significant differences in their niches
A species’ fundamental niche is the niche potentially occupied by that species A species’ realized niche is the niche actually occupied by that species As a result of competition, a species’ fundamental niche may differ from its realized niche For example, the presence of one barnacle species limits the realized niche of another species
Figure 54. 3 Experiment Chthamalus Balanus High tide Chthamalus realized niche Balanus realized niche Ocean Results Low tide High tide Chthamalus fundamental niche Ocean © 2014 Pearson Education, Inc. Low tide
Community interactions: (+, 0) or (+, +) or (+, -) Relationships between species in a community interspecific interactions Competition, predation, herbivory, symbiosis (parasitism, mutualism, and commensalism), and facilitation Can affect the survival and reproduction of each species: ( ), (0)
Competition Interspecific competition ( / interaction) occurs when species compete for a resource in short supply Strong competition can lead to competitive exclusion, local elimination of a competing species Competitive Exclusion Principle Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community
Figure 54. 2 A. distichus perches on fence posts and other sunny surfaces. A. insolitus usually perches on shady branches. A. ricordi A. aliniger A. distichus A. insolitus A. christophei A. cybotes A. etheridgei © 2014 Pearson Education, Inc.
Figure 54. UN 02 The golden spiny mouse (Acomys russatus) © 2014 Pearson Education, Inc.
Predation (+/-) One species, the predator, kills and eats the other, the prey Some feeding adaptations of predators are claws, fangs, and poison Prey display various defensive adaptations - hide, flee, form herds/schools, self-defense, & alarm calls - morphological, physiological defense - mechanical & chemical defenses
Figure 54. 5 (a) Mechanical defense (b) Chemical defense ▶ Porcupine ▶ Skunk (c) Aposematic coloration: warning coloration (d) Cryptic coloration: camouflage ◀ Poison dart frog (e) Batesian mimicry: A harmless species mimics a harmful one. (f) Müllerian mimicry: Two unpalatable species mimic each other. ▲ Venomous green parrot snake © 2014 Pearson Education, Inc. ▶ Canyon tree frog ◀ Nonvenomous hawkmoth larva ◀ Yellow jacket ◀ Cuckoo bee
Mimicry can also be used by predators to approach prey For example, the mimic octopus can take on the appearance and movement of more than a dozen marine animals
Figure 54. 6 (a) Mimicking a sea snake (b) Mimicking a flounder (c) Mimicking a stingray © 2014 Pearson Education, Inc.
Herbivory (+/-) Herbivore eats parts of a plant or alga It has led to evolution of plant mechanical and chemical defenses and adaptations by herbivores
Figure 54. 7 © 2014 Pearson Education, Inc.
Symbiosis is a relationship where two or more species live in direct and intimate contact with one another
Parasitism (+/-) The parasite, derives nourishment from another organism, its host, which is harmed in the process Parasites that live within the body of their host are called endoparasites Parasites that live on the external surface of a host are ectoparasites Social Parasites & Parasitoids
Mutualism (+/+) Interspecific interaction that benefits both species A mutualism can be Obligate, where one species cannot survive without the other Facultative, where both species can survive alone
Figure 54. 8 (a) Hollow thorns that house stinging ants of the genus Pseudomyrmex © 2014 Pearson Education, Inc. (b) Area cleared by ants around an acacia tree
Commensalism (+/0) One species benefits and the other is neither harmed nor helped Commensal interactions are hard to document in nature because any close association likely affects both species
Figure 54. 9 © 2014 Pearson Education, Inc.
Facilitation ( / or 0/ ) 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
Number of plant species Figure 54. 10 8 6 4 2 0 (a) Salt marsh with Juncus (foreground) © 2014 Pearson Education, Inc. (b) With Juncus Without Juncus
Species Diversity 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 54. 11 A B C D Community 1 A: 25% B: 25% C: 25% D: 25% © 2014 Pearson Education, Inc. Community 2 A: 80% B: 5% C: 5% D: 10%
Communities with higher diversity are More productive; they produce more biomass (the total mass of all organisms) More stable in their productivity Better able to withstand recover from environmental stresses More resistant to invasive species, organisms that become established outside their native range
Figure 54. UN 07 Interspecific Interaction Description Interspecific competition (−/−) Two or more species compete for a resource that is in short supply. Predation (+/−) One species, the predator, kills and eats the other, the prey. Predation has led to diverse adaptations, including mimicry. Herbivory (+/−) An herbivore eats part of a plant or alga. Symbiosis Individuals of two or more species live in close contact with one another. Symbiosis includes parasitism, mutualism and commensalism. Parasitism (+/−) The parasite derives its nourishment from a second organism, its host, which is harmed. Mutualism (+/+) Both species benefit from the interaction. Commensalism (+/0) One species benefits from the interaction, while the other is unaffected by it. Facilitation (+/+ or 0/+) © 2014 Pearson Education, Inc. Species have positive effects on the survival and reproduction of other species without the intimate contact of a symbiosis.
ECOSYSTEM ECOLOGY �An ecosystem includes �the community of species in a given area and �all the abiotic factors, such as � Energy � Biogeochemical © 2013 Pearson Education, Inc. Cycles
emical c ycl ing h C Energy flow Light energy Chemical energy Bacteria, protists, and fungi Chemical elements Heat energy
Trophic Structure Trophic structure is the feeding relationships between organisms in a community It is a key factor in community dynamics Food chains link trophic levels from producers to top carnivores
Figure 54. 14 Carnivore Quaternary consumers Carnivore Tertiary consumers Carnivore Secondary consumers Carnivore Herbivore Primary consumers Zooplankton Plant Primary producers Phytoplankton A terrestrial food chain © 2014 Pearson Education, Inc. A marine food chain
Food Webs A food web is a branching food chain with complex trophic interactions Species may play a role at more than one trophic level Food webs can be simplified by Grouping species with similar trophic relationships into broad functional groups Isolating a portion of a community that interacts very little with the rest of the community
Quaternary, tertiary, and secondary consumers Tertiary and secondary consumers Secondary and primary consumers Producers (plants)
Figure 54. 15 Humans Smaller toothed whales Baleen whales Crabeater seals Birds Leopard seals Fishes Sperm whales Elephant seals Squids Carnivorous plankton Copepods Krill Phytoplankton © 2014 Pearson Education, Inc.
The energetic hypothesis suggests that length is limited by inefficient energy transfer Only about 10% of the energy stored in organic matter at each trophic level is converted to organic matter at the next trophic level For example, a producer level consisting of 100 kg of plant material can support about 10 kg of herbivore biomass and 1 kg of carnivore biomass
Tertiary consumers 10 kcal Secondary consumers 100 kcal Primary consumers Producers 1, 000 kcal 10, 000 kcal 1, 000 kcal of sunlight
Species with a Large Impact Certain species have a very large impact on community & ecosystem structure Such species are highly abundant or play a pivotal role in community dynamics
Dominant species most abundant or have the highest biomass One hypothesis suggests that dominant species are most competitive in exploiting resources Another hypothesis is that they are most successful at avoiding predators Invasive species, typically introduced to a new environment by humans, may become dominant because they lack predators or disease
Keystone species exert strong control on a community by their ecological roles, or niches In contrast to dominant species, they are not necessarily abundant in a community Field studies of sea stars illustrate their role as a keystone species in intertidal communities
Figure 54. 18 Experiment Number of species present Results © 2014 Pearson Education, Inc. 20 15 10 5 0 With Pisaster (control) Without Pisaster (experimental) 1963 ′ 64 ′ 65 ′ 66 ′ 67 ′ 68 ′ 69 ′ 70 ′ 71 ′ 72 ′ 73 Year
The General Scheme of Chemical Cycling �Biogeochemical cycles involve �biotic components and �abiotic components from an abiotic reservoir where a chemical accumulates or is stockpiled outside of living organisms. © 2013 Pearson Education, Inc.
Consumers 3 2 Producers 1 Decomposers Nutrients available to producers Abiotic reservoir Geologic processes 4
5 Burning CO 2 in atmosphere 3 Cellular respiration Photosynthesis 1 Higher-level consumers Plants, algae, cyanobacteria Primary consumers Wood and fossil fuels 2 Decomposition Wastes; death Decomposers (soil microbes) 4 Detritus Plant litter; death
6 Uplifting of rock 3 Weathering of rock Phosphates in rock Runoff Animals Plants 1 Phosphates in solution 5 Rock Solid phosphates Assimilation 2 Phosphates in soil (inorganic) 4 Detritus Decomposers in soil Decomposition
N 2 in atmosphere 8 Plant Denitrifying bacteria 4 Nitrifying bacteria 1 Death; wastes 5 NO 3− in soil 6 Animal Detritus Nitrogen-fixing bacteria in root nodules 7 Decomposers Free-living nitrogen-fixing bacteria 3 NH 4 in soil 2
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