Figure 40.16 Idealized survivorship curves: types I, II, and III 1,000 I 100 II Number of survivors (log scale) 10 A life table is an age-specific summary of the survival pattern of a population. It is best made by following the fate of a cohort, a group of individuals of the same age, from birth to death. A survivorship curve is a graphic way of representing the data in a life table. Survivorship curves plot the proportion or numbers of a cohort still alive at each age. Survivorship curves can be classified into three general types Type I: low death rates during early and middle life and an increase in death rates among older age groups Type II: a constant death rate over the organism’s life span Type III: high death rates for the young and a lower death rate for survivors Many species are intermediate to these curves. III 1 50 100 Percentage of maximum life span 1

Chapter 41 Species Interactions

You Must Know The difference between a fundamental niche and a realized niche. The role of competitive exclusion in interspecific competition. The symbiotic relationships of parasitism, mutualism, and commensalism.

Interspecific competition occurs when species compete for a resource that limits their growth or survival. (−/− interaction) Ecologists call relationships between different species in a community interspecific interactions. 4

Competitive Exclusion The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place. Strong competition can lead to competitive exclusion, local elimination of a competing species 5

Ecological Niches and Natural Selection Ecological niche, the specific set of biotic and abiotic resources used by an organism. Ecologically similar species can coexist in a community if there are one or more significant differences in their niches. 6

Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community. Harvester Ants Video Clip 7

Experiment High tide Chthamalus Balanus Chthamalus realized niche A species’ realized niche is the niche actually occupied by that species. Balanus realized niche Low tide High tide A species’ fundamental niche is the niche potentially 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. Results Chthamalus fundamental niche Ocean Low tide 8

Predation /− interaction Video Clip – Ants and Termites Predation (/− interaction) refers to an interaction in which one species, the predator, kills and eats the other, the prey. Some feeding adaptations of predators are claws, teeth, stingers, and poison. Video Clip – Ants and Termites /− interaction 9

Behavioral Defenses Hiding Fleeing Active self-defense Schooling Prey display various behavioral defensive adaptations. Behavioral defenses include hiding, fleeing, forming herds or schools, and active self-defense. Active self-defense Schooling 10

Morphological and Physiological Defense Adaptations (a) Cryptic coloration (b) Aposematic coloration Canyon tree frog Poison dart frog (c) Batesian mimicry: A harmless species mimics a harmful one. Nonvenomous hawkmoth larva (d) Müllerian mimicry: Two unpalatable species mimic each other. Animals also have morphological and physiological defense adaptations Cryptic coloration, or camouflage, makes prey difficult to spot. Animals with effective chemical defenses often exhibit bright warning coloration, called aposematic coloration. Predators are particularly cautious in dealing with prey that display such coloration. In some cases, a prey species may gain significant protection by mimicking the appearance of another species. In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model. In Müllerian mimicry, two or more unpalatable species resemble each other. Venomous green parrot snake Cuckoo bee Yellow jacket 11

Herbivory (/− interaction) Herbivory (/− interaction) refers to an interaction in which an herbivore eats parts of a plant or alga. In addition to behavioral adaptations, some herbivores may have chemical sensors or specialized teeth or digestive systems. Plant defenses include chemical toxins and protective structures. 12

Symbiosis Symbiosis is a relationship where two or more species live in direct and intimate contact with one another. 13

Parasitism /− interaction In parasitism (/− interaction), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process. /− interaction 14

Some parasites change the behavior of the host in a way that increases the parasites’ fitness. Parasites can significantly affect survival, reproduction, and density of host populations Fungus Video 15

Mutualism / interaction Video Clip - Hippo Mutualistic symbiosis, or mutualism (/ interaction), is an interspecific interaction that benefits both species. In some mutualisms, one species cannot survive without the other. In other mutualisms, both species can survive alone. Mutualisms sometimes involve coevolution of related adaptations in both species. / interaction Video Clip - Hippo 16

/0 interaction Commensalism In commensalism (/0 interaction), one species benefits and the other is neither harmed nor helped. /0 interaction 17

Facilitation Facilitation (/ or 0/) is an interaction in which one species has positive effects on another species without direct and intimate contact. 8 6 Number of plant species For example, the black rush makes the soil more hospitable for other plant species 4 2 (a) Salt marsh with Juncus (foreground) With Juncus Without Juncus (b) 18