Figure 49.14 upper left 7.014 Lecture 33 May 9 Species Interactions – Competition 2007 Consumptive competition occurs when organisms compete for the same resources. These trees are competing for nitrogen and other nutrients. Figure 49.14 upper right Figure 49.14 middle left Preemptive competition occurs when individuals occupy space and prevent access Overgrowth competition occurs when an organism grows over another, blocking to resources by other individuals. The space preempted by these barnacles is access to resources. This large fern has overgrown other individuals and is unavailable to competitors. shading them. 1 Figure 49.14 middle right Figure 49.14 lower left Chemical competition occurs when one species produces toxins that negatively Territorial competition occurs when mobile organisms protect a feeding or affect another. Note how few plants are growing under these Salvia shrubs. breeding territory. These red-winged blackbirds are displaying to each other at a territorial boundary. Figure 49.14 lower left The Fundamental Ecological Niche: “An n-dimensional hyper-volume every point on which a species can survive and reproduce indefinitely in the absence of other species” (Hutchinson) y t i d i m u h e iz tem s pe d Encounter competition occurs when organisms interfere directly with each other’s ra oo tur F access to specific resources. Here, spotted hyenas and vultures fight over a kill. e 2 The Realized Ecological Niche: the niche actually occupied in the presence of other species niche overlap leads to competition y t i d i y t i m d u i h m u h e te iz e m s t iz per od em s atu o pe d re F rat oo ure F Figure 49.13a Figure 49.13b Partial niche overlap can lead to Partial niche overlap: One species eats seeds of one size range competition for seeds of Niche Partitioning and intermediate size Competitive Coexistence Species 2 d e m Species 1 u d s e n m o c u s r n e o b c m r u e N b m u N Seed size (one niche dimension Seed size 3 Figure 49.13c The Spread of Introduced Zebra Mussels in the Strong niche overlap can lead United States (1998 – 2001) Complete niche overlap to Competitive Exclusion Species 1: Strong competitor d e m u s Species 2: Weak competitor, n o driven to extinction c r e b Extensive m u N niche overlap can lead to competitive exclusion Seed size Figure 49.15a Observed Distributions: Is this due to competition? Connell’s Barnacles Pelagic larvae Or differential tolerance of desiccation? are sessile as Do an Experiment! adults Chthamalus A classic ecological experiment in upper intertidal zone demonstrating niche partitioning Mean tidal level Balanus in lower intertidal zone 4 Figure 49.15b COMPETITION EXPERIMENT Chthamalus survives better without competition. 1. Transplant rocks Upper containing young 100 intertidal Chthamalus to lower intertidal. Competitor present Lower intertidal 80 y t i l a Competitor present 2. Let Balanus t colonize the rocks. r 60 o m t Competitor Chthamalus n absent e Balanus c 40 r e P Competitor 3. Remove Balanus absent from one-half of 20 each rock. Monitor survival of Chthamalus on both sides. 0 Young Chthamalus Older Chthamalus On which side of the rocks do Chthamalus survive better? Figure 49.15c 54.17 Barnacles Purves Larval Pelagic larvae Larval Adult subject to Connell’s Barnacles Settlement desiccation are sessile as Settlement Distribution Zone Zone adults Spring high tide Adult Fundamental Realized Distribution Niche Niche Chthamalus Neap high tide Could not become adults due to competition Mean tidal level Chthamalus is resistant to Balanus Balanus outcompetes Chthamalus desiccation but is outcompeted but is more vulnerable to desiccation by Balanus Neap low tide Spring low tide Distribution of Two Barnacle Species – Balanus and Chthamalus 5 Stabilizing Selection Directional Selection Medium-sized individuals favored Larger individuals favored Number of Reduces Number of Individuals Variation Individuals with with phenotype phenotype 0 10 20 30 40 50 0 10 20 30 40 50 Peak gets higher and narrower Peak shifts in one direction Selection Selection Mean Shifts Mean stays the same 0 10 20 30 40 50 0 10 20 30 40 50 Directional Selection African Seedcracker Large and small individuals favored (Pyrenestes ostrinus) Number of Individuals with phenotype Birds with smaller bills Birds with large can consume soft bills can crack 100 0 10 20 30 40 50 seeds more efficiently hard seeds s d r Two Peaks i B f Birds with o 50 Selection Two populations r intermediate beak e size survive forming b m poorly Competition can u N lead to character 0 displacement 30 40 50 10 15 20 Width of lower bill (mm) 6 Niche Partitioning can lead to ANCESTOR FINCH Adaptive Blue-back grassquit Radiation Sharp-billed ground finch Vegetarian finch Hawaiian Mangrove Small tree Large Honeycreepers finch finch cactus Large finch Large tree finch Cactus finch ground Medium tree finch finch Woodpecker finch Warbler finch Medium ground finch Adaptive Radiation to Exploit a Variety of Food Insect Eaters Bud Eaters Seed Eaters Sources Results in Speciation and a variety of Galapagos Finches Beak Shapes 7.