Plant Ecology - Chapter 10 Competition

Reduction in fitness due to shared use of a resource that is in limited supply Intraspecific Interspecific

Competition - / - both parties lose 0 / - or + / - asymmetric competition - largest individuals have disproportionate negative effects on their smaller neighbors

Competition Small head start may confer a large size advantage - competitive dominance over later- emerging plants Self-thinning - higher early mortality in smaller or weaker individuals in overly dense plantings

Competition Competing for light, water and mineral nutrients from the soil, space to grow and acquire resources, access to mates Competitive interactions experienced by a plant occur very locally

Competition Immediate density most important - average density essentially irrelevant Effects of neighbors decrease sharply with distance

Competition Winning the competition for light may affect all other competition

Competition Tall plants may intercept light, but small plants may intercept water, soil nutrients Asymmetric, but larger plants usually have much greater effects

Competition Trade-offs and strategies Winning competition for one resource may compromise ability to win comp. for another (light vs. nutrients) Outcome may change as resource availability changes

Allelopathy - Allelochemicals Chemical warfare among neighboring plants Release toxins into soil to reduce growth or kill adjacent plants Sure way to gain competitive advantage Knapweed on rangelands - little effect on Eurasian plants, strong effects on N. Amer. plants

Facilitation Positive effects on neighbors rather than negative (opposite of competition?) May be particularly common under conditions of high abiotic stress, or high herbivory

Facilitation-nurse plants Mature “nurse” plant may facilitate germination, establishment, growth of juvenile plant of a different growth form Particularly common in deserts, e.g. columnar cactus established with help of nurse shrub

Facilitation-CMNs Common mycorrhizal networks - extensive connections linking many plants of differing age, species May facilitate seedling and sapling survival and growth by way of nutrient and water transfers among plants Mature helping juvenile

Competition Models Lotka-Volterra model not very useful for plants, since plants don’t experience the average effects of density the same way animals do Two different groups of models developed for plants

Competition Models Equilibrium models - how different the niches of species need to be to prevent competitive exclusion at equilibrium

Competition Models Nonequilibrium models - emphasize importance of resource variation (in time, space) and competition affecting coexistence

Competition Debate Are there predictable competitive hierarchies across different communities?

Competition Debate Is competition more intense in high- productivity than low-productivity environments?

Competition Debate How important is competition compared to other forces in determining species distributions and community composition?

Competition Debate No general consensus on any of these yet